diff --git a/CHANGELOG.md b/CHANGELOG.md
index c3bb9e7edc..9118916cd5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ## Unreleased - TBD
 
+### MINOR BREAKING CHANGE
+
+- Typing was strengthened by leveraging native typing. While this should not change any behavior, it might need minor
+  adaption of your code if you use static analysis tools such as PHPStan or
+  Psalm. [PR #3718](https://github.com/PHPOffice/PhpSpreadsheet/pull/3718)
+
 ### Added
 
 - Split screens (Xlsx and Xml only, not 100% complete). [Issue #3601](https://github.com/PHPOffice/PhpSpreadsheet/issues/3601) [PR #3622](https://github.com/PHPOffice/PhpSpreadsheet/pull/3622)
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index b894ce1381..f6ce123adc 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -19,8 +19,5 @@ parameters:
         processTimeout: 300.0
     checkMissingIterableValueType: false
     ignoreErrors:
-        - '~^Parameter \#1 \$im(age)? of function (imagedestroy|imageistruecolor|imagealphablending|imagesavealpha|imagecolortransparent|imagecolorsforindex|imagesavealpha|imagesx|imagesy|imagepng|imagecolorat) expects (GdImage|resource), GdImage\|resource given\.$~'
-        - '~^Parameter \#2 \$src_im(age)? of function imagecopy expects (GdImage|resource), GdImage\|resource given\.$~'
         # Accept a bit anything for assert methods
         - '~^Parameter \#2 .* of static method PHPUnit\\Framework\\Assert\:\:assert\w+\(\) expects .*, .* given\.$~'
-        - '~^Method PhpOffice\\PhpSpreadsheetTests\\.*\:\:test.*\(\) has parameter \$args with no type specified\.$~'
diff --git a/src/PhpSpreadsheet/Calculation/Calculation.php b/src/PhpSpreadsheet/Calculation/Calculation.php
index ef4fb6ce0d..18bdd63470 100644
--- a/src/PhpSpreadsheet/Calculation/Calculation.php
+++ b/src/PhpSpreadsheet/Calculation/Calculation.php
@@ -74,10 +74,8 @@ class Calculation
 
     /**
      * Instance of the spreadsheet this Calculation Engine is using.
-     *
-     * @var ?Spreadsheet
      */
-    private $spreadsheet;
+    private ?Spreadsheet $spreadsheet;
 
     /**
      * Calculation cache.
@@ -93,10 +91,7 @@ class Calculation
      */
     private $calculationCacheEnabled = true;
 
-    /**
-     * @var BranchPruner
-     */
-    private $branchPruner;
+    private BranchPruner $branchPruner;
 
     /**
      * @var bool
@@ -127,10 +122,8 @@ class Calculation
 
     /**
      * The debug log generated by the calculation engine.
-     *
-     * @var Logger
      */
-    private $debugLog;
+    private Logger $debugLog;
 
     /**
      * Flag to determine how formula errors should be handled
@@ -155,17 +148,13 @@ class Calculation
 
     /**
      * Reference Helper.
-     *
-     * @var ReferenceHelper
      */
-    private static $referenceHelper;
+    private static ReferenceHelper $referenceHelper;
 
     /**
      * An array of the nested cell references accessed by the calculation engine, used for the debug log.
-     *
-     * @var CyclicReferenceStack
      */
-    private $cyclicReferenceStack;
+    private CyclicReferenceStack $cyclicReferenceStack;
 
     /** @var array */
     private $cellStack = [];
@@ -3018,7 +3007,7 @@ public static function getFALSE(): string
      *
      * @return bool Success or failure
      */
-    public static function setArrayReturnType($returnType)
+    public static function setArrayReturnType($returnType): bool
     {
         if (
             ($returnType == self::RETURN_ARRAY_AS_VALUE) ||
@@ -3164,10 +3153,8 @@ private function getLocaleFile(string $localeDir, string $locale, string $langua
      * Set the locale code.
      *
      * @param string $locale The locale to use for formula translation, eg: 'en_us'
-     *
-     * @return bool
      */
-    public function setLocale(string $locale)
+    public function setLocale(string $locale): bool
     {
         //    Identify our locale and language
         $language = $locale = strtolower($locale);
@@ -3341,12 +3328,7 @@ private static function translateFormula(array $from, array $to, string $formula
     /** @var ?array */
     private static $functionReplaceToLocale;
 
-    /**
-     * @param string $formula
-     *
-     * @return string
-     */
-    public function _translateFormulaToLocale($formula)
+    public function _translateFormulaToLocale(string $formula): string
     {
         // Build list of function names and constants for translation
         if (self::$functionReplaceFromExcel === null) {
@@ -3384,12 +3366,7 @@ public function _translateFormulaToLocale($formula)
     /** @var ?array */
     private static $functionReplaceToExcel;
 
-    /**
-     * @param string $formula
-     *
-     * @return string
-     */
-    public function _translateFormulaToEnglish($formula)
+    public function _translateFormulaToEnglish(string $formula): string
     {
         if (self::$functionReplaceFromLocale === null) {
             self::$functionReplaceFromLocale = [];
@@ -3438,11 +3415,9 @@ public static function localeFunc($function)
     /**
      * Wrap string values in quotes.
      *
-     * @param mixed $value
-     *
      * @return mixed
      */
-    public static function wrapResult($value)
+    public static function wrapResult(mixed $value)
     {
         if (is_string($value)) {
             //    Error values cannot be "wrapped"
@@ -3783,10 +3758,8 @@ public function _calculateFormulaValue($formula, $cellID = null, ?Cell $cell = n
      *                                            0 = no resize
      *                                            1 = shrink to fit
      *                                            2 = extend to fit
-     *
-     * @return array
      */
-    private static function checkMatrixOperands(&$operand1, &$operand2, $resize = 1)
+    private static function checkMatrixOperands(&$operand1, &$operand2, $resize = 1): array
     {
         //    Examine each of the two operands, and turn them into an array if they aren't one already
         //    Note that this function should only be called if one or both of the operand is already an array
@@ -3824,7 +3797,7 @@ private static function checkMatrixOperands(&$operand1, &$operand2, $resize = 1)
      *
      * @return int[] An array comprising the number of rows, and number of columns
      */
-    public static function getMatrixDimensions(array &$matrix)
+    public static function getMatrixDimensions(array &$matrix): array
     {
         $matrixRows = count($matrix);
         $matrixColumns = 0;
@@ -3845,14 +3818,14 @@ public static function getMatrixDimensions(array &$matrix)
     /**
      * Ensure that paired matrix operands are both matrices of the same size.
      *
-     * @param mixed $matrix1 First matrix operand
-     * @param mixed $matrix2 Second matrix operand
+     * @param array $matrix1 First matrix operand
+     * @param array $matrix2 Second matrix operand
      * @param int $matrix1Rows Row size of first matrix operand
      * @param int $matrix1Columns Column size of first matrix operand
      * @param int $matrix2Rows Row size of second matrix operand
      * @param int $matrix2Columns Column size of second matrix operand
      */
-    private static function resizeMatricesShrink(&$matrix1, &$matrix2, $matrix1Rows, $matrix1Columns, $matrix2Rows, $matrix2Columns): void
+    private static function resizeMatricesShrink(array &$matrix1, array &$matrix2, $matrix1Rows, $matrix1Columns, $matrix2Rows, $matrix2Columns): void
     {
         if (($matrix2Columns < $matrix1Columns) || ($matrix2Rows < $matrix1Rows)) {
             if ($matrix2Rows < $matrix1Rows) {
@@ -3888,14 +3861,14 @@ private static function resizeMatricesShrink(&$matrix1, &$matrix2, $matrix1Rows,
     /**
      * Ensure that paired matrix operands are both matrices of the same size.
      *
-     * @param mixed $matrix1 First matrix operand
-     * @param mixed $matrix2 Second matrix operand
+     * @param array $matrix1 First matrix operand
+     * @param array $matrix2 Second matrix operand
      * @param int $matrix1Rows Row size of first matrix operand
      * @param int $matrix1Columns Column size of first matrix operand
      * @param int $matrix2Rows Row size of second matrix operand
      * @param int $matrix2Columns Column size of second matrix operand
      */
-    private static function resizeMatricesExtend(&$matrix1, &$matrix2, $matrix1Rows, $matrix1Columns, $matrix2Rows, $matrix2Columns): void
+    private static function resizeMatricesExtend(array &$matrix1, array &$matrix2, $matrix1Rows, $matrix1Columns, $matrix2Rows, $matrix2Columns): void
     {
         if (($matrix2Columns < $matrix1Columns) || ($matrix2Rows < $matrix1Rows)) {
             if ($matrix2Columns < $matrix1Columns) {
@@ -3976,10 +3949,8 @@ private function showValue($value)
      * Format type and details of an operand for display in the log (based on operand type).
      *
      * @param mixed $value First matrix operand
-     *
-     * @return null|string
      */
-    private function showTypeDetails($value)
+    private function showTypeDetails($value): ?string
     {
         if ($this->debugLog->getWriteDebugLog()) {
             $testArray = Functions::flattenArray($value);
@@ -4013,11 +3984,9 @@ private function showTypeDetails($value)
     }
 
     /**
-     * @param string $formula
-     *
      * @return false|string False indicates an error
      */
-    private function convertMatrixReferences($formula)
+    private function convertMatrixReferences(string $formula): false|string
     {
         static $matrixReplaceFrom = [self::FORMULA_OPEN_MATRIX_BRACE, ';', self::FORMULA_CLOSE_MATRIX_BRACE];
         static $matrixReplaceTo = ['MKMATRIX(MKMATRIX(', '),MKMATRIX(', '))'];
@@ -4120,7 +4089,7 @@ private function convertMatrixReferences($formula)
      *
      * @return array<int, mixed>|false
      */
-    private function internalParseFormula($formula, ?Cell $cell = null)
+    private function internalParseFormula($formula, ?Cell $cell = null): bool|array
     {
         if (($formula = $this->convertMatrixReferences(trim($formula))) === false) {
             return false;
@@ -4444,6 +4413,7 @@ private function internalParseFormula($formula, ?Cell $cell = null)
                         } elseif ($val === Information\ExcelError::REF()) {
                             $stackItemReference = $val;
                         } else {
+                            /** @var non-empty-string $startRowColRef */
                             $startRowColRef = $output[count($output) - 1]['value'] ?? '';
                             [$rangeWS1, $startRowColRef] = Worksheet::extractSheetTitle($startRowColRef, true);
                             $rangeSheetRef = $rangeWS1;
@@ -4470,7 +4440,7 @@ private function internalParseFormula($formula, ?Cell $cell = null)
                                 $valx = $val;
                                 $endRowColRef = ($refSheet !== null) ? $refSheet->getHighestDataColumn($valx) : AddressRange::MAX_COLUMN; //    Max 16,384 columns for Excel2007
                                 $val = "{$rangeWS2}{$endRowColRef}{$val}";
-                            } elseif (ctype_alpha($val) && strlen($val) <= 3) {
+                            } elseif (ctype_alpha($val) && strlen($val ?? '') <= 3) {
                                 //    Column range
                                 $stackItemType = 'Column Reference';
                                 $endRowColRef = ($refSheet !== null) ? $refSheet->getHighestDataRow($val) : AddressRange::MAX_ROW; //    Max 1,048,576 rows for Excel2007
@@ -4614,11 +4584,9 @@ private function internalParseFormula($formula, ?Cell $cell = null)
     }
 
     /**
-     * @param array $operandData
-     *
      * @return mixed
      */
-    private static function dataTestReference(&$operandData)
+    private static function dataTestReference(array &$operandData)
     {
         $operand = $operandData['value'];
         if (($operandData['reference'] === null) && (is_array($operand))) {
@@ -4807,6 +4775,7 @@ private function processTokenStack($tokens, $cellID = null, ?Cell $cell = null)
                         } else {
                             $sheet1 = ($pCellWorksheet !== null) ? $pCellWorksheet->getTitle() : '';
                         }
+                        $sheet1 ??= '';
 
                         [$sheet2, $operand2Data['reference']] = Worksheet::extractSheetTitle($operand2Data['reference'], true);
                         if (empty($sheet2)) {
@@ -4837,7 +4806,7 @@ private function processTokenStack($tokens, $cellID = null, ?Cell $cell = null)
                                 }
                             }
 
-                            $oData = array_merge(explode(':', $operand1Data['reference']), explode(':', $operand2Data['reference']));
+                            $oData = array_merge(explode(':', $operand1Data['reference'] ?? ''), explode(':', $operand2Data['reference'] ?? ''));
                             $oCol = $oRow = [];
                             $breakNeeded = false;
                             foreach ($oData as $oDatum) {
@@ -5224,10 +5193,8 @@ private function processTokenStack($tokens, $cellID = null, ?Cell $cell = null)
     /**
      * @param mixed $operand
      * @param mixed $stack
-     *
-     * @return bool
      */
-    private function validateBinaryOperand(&$operand, &$stack)
+    private function validateBinaryOperand(&$operand, &$stack): bool
     {
         if (is_array($operand)) {
             if ((count($operand, COUNT_RECURSIVE) - count($operand)) == 1) {
@@ -5268,11 +5235,8 @@ private function validateBinaryOperand(&$operand, &$stack)
     /**
      * @param mixed $operand1
      * @param mixed $operand2
-     * @param string $operation
-     *
-     * @return array
      */
-    private function executeArrayComparison($operand1, $operand2, $operation, Stack &$stack, bool $recursingArrays)
+    private function executeArrayComparison($operand1, $operand2, string $operation, Stack &$stack, bool $recursingArrays): array
     {
         $result = [];
         if (!is_array($operand2)) {
@@ -5314,12 +5278,8 @@ private function executeArrayComparison($operand1, $operand2, $operation, Stack
     /**
      * @param mixed $operand1
      * @param mixed $operand2
-     * @param string $operation
-     * @param bool $recursingArrays
-     *
-     * @return mixed
      */
-    private function executeBinaryComparisonOperation($operand1, $operand2, $operation, Stack &$stack, $recursingArrays = false)
+    private function executeBinaryComparisonOperation($operand1, $operand2, string $operation, Stack &$stack, bool $recursingArrays = false): array|bool
     {
         //    If we're dealing with matrix operations, we want a matrix result
         if ((is_array($operand1)) || (is_array($operand2))) {
@@ -5476,7 +5436,7 @@ private function executeNumericBinaryOperation($operand1, $operand2, $operation,
      *
      * @return false
      */
-    protected function raiseFormulaError(string $errorMessage, int $code = 0, ?Throwable $exception = null)
+    protected function raiseFormulaError(string $errorMessage, int $code = 0, ?Throwable $exception = null): bool
     {
         $this->formulaError = $errorMessage;
         $this->cyclicReferenceStack->clear();
@@ -5495,9 +5455,9 @@ protected function raiseFormulaError(string $errorMessage, int $code = 0, ?Throw
      * @param Worksheet $worksheet Worksheet
      * @param bool $resetLog Flag indicating whether calculation log should be reset or not
      *
-     * @return mixed Array of values in range if range contains more than one element. Otherwise, a single value is returned.
+     * @return array Array of values in range if range contains more than one element. Otherwise, a single value is returned.
      */
-    public function extractCellRange(&$range = 'A1', ?Worksheet $worksheet = null, $resetLog = true)
+    public function extractCellRange(&$range = 'A1', ?Worksheet $worksheet = null, bool $resetLog = true): array
     {
         // Return value
         $returnValue = [];
@@ -5547,9 +5507,9 @@ public function extractCellRange(&$range = 'A1', ?Worksheet $worksheet = null, $
      * @param null|Worksheet $worksheet Worksheet
      * @param bool $resetLog Flag indicating whether calculation log should be reset or not
      *
-     * @return mixed Array of values in range if range contains more than one element. Otherwise, a single value is returned.
+     * @return array|string Array of values in range if range contains more than one element. Otherwise, a single value is returned.
      */
-    public function extractNamedRange(string &$range = 'A1', ?Worksheet $worksheet = null, $resetLog = true)
+    public function extractNamedRange(string &$range = 'A1', ?Worksheet $worksheet = null, bool $resetLog = true): string|array
     {
         // Return value
         $returnValue = [];
@@ -5607,10 +5567,8 @@ public function extractNamedRange(string &$range = 'A1', ?Worksheet $worksheet =
      * Is a specific function implemented?
      *
      * @param string $function Function Name
-     *
-     * @return bool
      */
-    public function isImplemented($function)
+    public function isImplemented($function): bool
     {
         $function = strtoupper($function);
         $notImplemented = !isset(self::$phpSpreadsheetFunctions[$function]) || (is_array(self::$phpSpreadsheetFunctions[$function]['functionCall']) && self::$phpSpreadsheetFunctions[$function]['functionCall'][1] === 'DUMMY');
@@ -5628,10 +5586,8 @@ public static function getFunctions(): array
 
     /**
      * Get a list of implemented Excel function names.
-     *
-     * @return array
      */
-    public function getImplementedFunctionNames()
+    public function getImplementedFunctionNames(): array
     {
         $returnValue = [];
         foreach (self::$phpSpreadsheetFunctions as $functionName => $function) {
@@ -5697,12 +5653,9 @@ private function getArgumentDefaultValue(ReflectionParameter $methodArgument)
     /**
      * Add cell reference if needed while making sure that it is the last argument.
      *
-     * @param bool $passCellReference
      * @param array|string $functionCall
-     *
-     * @return array
      */
-    private function addCellReference(array $args, $passCellReference, $functionCall, ?Cell $cell = null)
+    private function addCellReference(array $args, bool $passCellReference, $functionCall, ?Cell $cell = null): array
     {
         if ($passCellReference) {
             if (is_array($functionCall)) {
diff --git a/src/PhpSpreadsheet/Calculation/Database.php b/src/PhpSpreadsheet/Calculation/Database.php
index 017c57106b..547d6062c3 100644
--- a/src/PhpSpreadsheet/Calculation/Database.php
+++ b/src/PhpSpreadsheet/Calculation/Database.php
@@ -25,7 +25,7 @@ class Database
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -71,12 +71,10 @@ public static function DAVERAGE($database, $field, $criteria)
      *                                        the column label in which you specify a condition for the
      *                                        column.
      *
-     * @return int|string
-     *
      * @TODO    The field argument is optional. If field is omitted, DCOUNT counts all records in the
      *            database that match the criteria.
      */
-    public static function DCOUNT($database, $field, $criteria)
+    public static function DCOUNT($database, $field, $criteria): string|int
     {
         return Database\DCount::evaluate($database, $field, $criteria);
     }
@@ -97,7 +95,7 @@ public static function DCOUNT($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -107,10 +105,8 @@ public static function DCOUNT($database, $field, $criteria)
      *                                        includes at least one column label and at least one cell below
      *                                        the column label in which you specify a condition for the
      *                                        column.
-     *
-     * @return int|string
      */
-    public static function DCOUNTA($database, $field, $criteria)
+    public static function DCOUNTA($database, $field, $criteria): string|int
     {
         return Database\DCountA::evaluate($database, $field, $criteria);
     }
@@ -132,7 +128,7 @@ public static function DCOUNTA($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -167,7 +163,7 @@ public static function DGET($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -202,7 +198,7 @@ public static function DMAX($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -236,7 +232,7 @@ public static function DMIN($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -271,7 +267,7 @@ public static function DPRODUCT($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -306,7 +302,7 @@ public static function DSTDEV($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -340,7 +336,7 @@ public static function DSTDEVP($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -375,7 +371,7 @@ public static function DSUM($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -410,7 +406,7 @@ public static function DVAR($database, $field, $criteria)
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DAverage.php b/src/PhpSpreadsheet/Calculation/Database/DAverage.php
index 245e970d6a..9388e469c7 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DAverage.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DAverage.php
@@ -19,7 +19,7 @@ class DAverage extends DatabaseAbstract
      *                          A database is a list of related data in which rows of related
      *                              information are records, and columns of data are fields. The
      *                              first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                              column label enclosed between double quotation marks, such as
      *                              "Age" or "Yield," or a number (without quotation marks) that
      *                              represents the position of the column within the list: 1 for
@@ -32,7 +32,7 @@ class DAverage extends DatabaseAbstract
      *
      * @return float|string
      */
-    public static function evaluate($database, $field, $criteria)
+    public static function evaluate($database, $field, $criteria): string|int|float
     {
         $field = self::fieldExtract($database, $field);
         if ($field === null) {
diff --git a/src/PhpSpreadsheet/Calculation/Database/DCount.php b/src/PhpSpreadsheet/Calculation/Database/DCount.php
index 66e1987e19..82795d84b7 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DCount.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DCount.php
@@ -30,10 +30,8 @@ class DCount extends DatabaseAbstract
      *                                        includes at least one column label and at least one cell below
      *                                        the column label in which you specify a condition for the
      *                                        column.
-     *
-     * @return int|string
      */
-    public static function evaluate($database, $field, $criteria, bool $returnError = true)
+    public static function evaluate($database, $field, $criteria, bool $returnError = true): string|int
     {
         $field = self::fieldExtract($database, $field);
         if ($returnError && $field === null) {
diff --git a/src/PhpSpreadsheet/Calculation/Database/DCountA.php b/src/PhpSpreadsheet/Calculation/Database/DCountA.php
index 214c20b7b2..fee8e5a547 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DCountA.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DCountA.php
@@ -19,7 +19,7 @@ class DCountA extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -29,10 +29,8 @@ class DCountA extends DatabaseAbstract
      *                                        includes at least one column label and at least one cell below
      *                                        the column label in which you specify a condition for the
      *                                        column.
-     *
-     * @return int|string
      */
-    public static function evaluate($database, $field, $criteria)
+    public static function evaluate($database, $field, $criteria): string|int
     {
         $field = self::fieldExtract($database, $field);
         if ($field === null) {
diff --git a/src/PhpSpreadsheet/Calculation/Database/DGet.php b/src/PhpSpreadsheet/Calculation/Database/DGet.php
index 5647cba5cc..4a52f2e416 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DGet.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DGet.php
@@ -19,7 +19,7 @@ class DGet extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DMax.php b/src/PhpSpreadsheet/Calculation/Database/DMax.php
index 748fd2fc84..512557ccc2 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DMax.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DMax.php
@@ -20,7 +20,7 @@ class DMax extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DMin.php b/src/PhpSpreadsheet/Calculation/Database/DMin.php
index 544cbffefb..ce01a0debc 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DMin.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DMin.php
@@ -20,7 +20,7 @@ class DMin extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DProduct.php b/src/PhpSpreadsheet/Calculation/Database/DProduct.php
index 351ee6fc22..c420ab6b55 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DProduct.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DProduct.php
@@ -19,7 +19,7 @@ class DProduct extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -29,10 +29,8 @@ class DProduct extends DatabaseAbstract
      *                                        includes at least one column label and at least one cell below
      *                                        the column label in which you specify a condition for the
      *                                        column.
-     *
-     * @return float|string
      */
-    public static function evaluate($database, $field, $criteria)
+    public static function evaluate($database, $field, $criteria): string|float
     {
         $field = self::fieldExtract($database, $field);
         if ($field === null) {
diff --git a/src/PhpSpreadsheet/Calculation/Database/DStDev.php b/src/PhpSpreadsheet/Calculation/Database/DStDev.php
index a1c56532fb..05418d490c 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DStDev.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DStDev.php
@@ -20,7 +20,7 @@ class DStDev extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DStDevP.php b/src/PhpSpreadsheet/Calculation/Database/DStDevP.php
index 5bca4e7232..927e29ceca 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DStDevP.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DStDevP.php
@@ -20,7 +20,7 @@ class DStDevP extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DSum.php b/src/PhpSpreadsheet/Calculation/Database/DSum.php
index ef4d10e809..aa8976bc8c 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DSum.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DSum.php
@@ -19,7 +19,7 @@ class DSum extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
diff --git a/src/PhpSpreadsheet/Calculation/Database/DVar.php b/src/PhpSpreadsheet/Calculation/Database/DVar.php
index 9cfa971482..d579ce357a 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DVar.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DVar.php
@@ -20,7 +20,7 @@ class DVar extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -33,7 +33,7 @@ class DVar extends DatabaseAbstract
      *
      * @return float|string (string if result is an error)
      */
-    public static function evaluate($database, $field, $criteria)
+    public static function evaluate($database, $field, $criteria): string|float
     {
         $field = self::fieldExtract($database, $field);
         if ($field === null) {
diff --git a/src/PhpSpreadsheet/Calculation/Database/DVarP.php b/src/PhpSpreadsheet/Calculation/Database/DVarP.php
index 67dbd68415..8a990d77c8 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DVarP.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DVarP.php
@@ -20,7 +20,7 @@ class DVarP extends DatabaseAbstract
      *                                        A database is a list of related data in which rows of related
      *                                        information are records, and columns of data are fields. The
      *                                        first row of the list contains labels for each column.
-     * @param int|string $field Indicates which column is used in the function. Enter the
+     * @param null|int|string $field Indicates which column is used in the function. Enter the
      *                                        column label enclosed between double quotation marks, such as
      *                                        "Age" or "Yield," or a number (without quotation marks) that
      *                                        represents the position of the column within the list: 1 for
@@ -33,7 +33,7 @@ class DVarP extends DatabaseAbstract
      *
      * @return float|string (string if result is an error)
      */
-    public static function evaluate($database, $field, $criteria)
+    public static function evaluate($database, $field, $criteria): string|float
     {
         $field = self::fieldExtract($database, $field);
         if ($field === null) {
diff --git a/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php b/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php
index 0b8c36dabe..d8b0d2094d 100644
--- a/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php
+++ b/src/PhpSpreadsheet/Calculation/Database/DatabaseAbstract.php
@@ -10,7 +10,7 @@ abstract class DatabaseAbstract
 {
     /**
      * @param array $database
-     * @param int|string $field
+     * @param null|int|string $field
      * @param array $criteria
      *
      * @return null|float|int|string
@@ -115,7 +115,7 @@ private static function buildQuery(array $criteriaNames, array $criteria): strin
         }
 
         $rowQuery = array_map(
-            function ($rowValue) {
+            function ($rowValue): string {
                 return (count($rowValue) > 1) ? 'AND(' . implode(',', $rowValue) . ')' : ($rowValue[0] ?? '');
             },
             $baseQuery
diff --git a/src/PhpSpreadsheet/Calculation/DateTime.php b/src/PhpSpreadsheet/Calculation/DateTime.php
index 26b667ca46..86a2114a25 100644
--- a/src/PhpSpreadsheet/Calculation/DateTime.php
+++ b/src/PhpSpreadsheet/Calculation/DateTime.php
@@ -20,7 +20,7 @@ class DateTime
      *
      * @return bool TRUE if the year is a leap year, otherwise FALSE
      */
-    public static function isLeapYear($year)
+    public static function isLeapYear($year): bool
     {
         return DateTimeExcel\Helpers::isLeapYear($year);
     }
@@ -34,9 +34,9 @@ public static function isLeapYear($year)
      *
      * @param mixed $dateValue
      *
-     * @return mixed Excel date/time serial value, or string if error
+     * @return float|string Excel date/time serial value, or string if error
      */
-    public static function getDateValue($dateValue)
+    public static function getDateValue($dateValue): float|string
     {
         try {
             return DateTimeExcel\Helpers::getDateValue($dateValue);
@@ -183,10 +183,10 @@ public static function DATE($year = 0, $month = 1, $day = 1)
      *                                    and seconds. For example, TIME(0,0,2000) = TIME(0,33,22) = .023148
      *                                    or 12:33:20 AM
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
+     * @return array|\DateTime|float|int|string Excel date/time serial value, PHP date/time serial value or PHP date/time object,
      *                        depending on the value of the ReturnDateType flag
      */
-    public static function TIME($hour = 0, $minute = 0, $second = 0)
+    public static function TIME($hour = 0, $minute = 0, $second = 0): string|float|int|\DateTime|array
     {
         return DateTimeExcel\Time::fromHMS($hour, $minute, $second);
     }
@@ -247,10 +247,10 @@ public static function DATEVALUE($dateValue)
      *                                    within quotation marks that represent time.
      *                                    Date information in time_text is ignored.
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
+     * @return array|\Datetime|float|int|string Excel date/time serial value, PHP date/time serial value or PHP date/time object,
      *                        depending on the value of the ReturnDateType flag
      */
-    public static function TIMEVALUE($timeValue)
+    public static function TIMEVALUE($timeValue): string|\Datetime|int|float|array
     {
         return DateTimeExcel\TimeValue::fromString($timeValue);
     }
@@ -334,7 +334,7 @@ public static function DAYS($endDate = 0, $startDate = 0)
      *
      * @return array|int|string Number of days between start date and end date
      */
-    public static function DAYS360($startDate = 0, $endDate = 0, $method = false)
+    public static function DAYS360($startDate = 0, $endDate = 0, $method = false): string|int|array
     {
         return DateTimeExcel\Days360::between($startDate, $endDate, $method);
     }
@@ -370,7 +370,7 @@ public static function DAYS360($startDate = 0, $endDate = 0, $method = false)
      *
      * @return array|float|string fraction of the year, or a string containing an error
      */
-    public static function YEARFRAC($startDate = 0, $endDate = 0, $method = 0)
+    public static function YEARFRAC($startDate = 0, $endDate = 0, $method = 0): string|int|float|array
     {
         return DateTimeExcel\YearFrac::fraction($startDate, $endDate, $method);
     }
@@ -398,7 +398,7 @@ public static function YEARFRAC($startDate = 0, $endDate = 0, $method = 0)
      *
      * @return array|int|string Interval between the dates
      */
-    public static function NETWORKDAYS($startDate, $endDate, ...$dateArgs)
+    public static function NETWORKDAYS($startDate, $endDate, ...$dateArgs): string|int|array
     {
         return DateTimeExcel\NetworkDays::count($startDate, $endDate, ...$dateArgs);
     }
@@ -451,7 +451,7 @@ public static function WORKDAY($startDate, $endDays, ...$dateArgs)
      *
      * @return array|int|string Day of the month
      */
-    public static function DAYOFMONTH($dateValue = 1)
+    public static function DAYOFMONTH($dateValue = 1): int|string|array
     {
         return DateTimeExcel\DateParts::day($dateValue);
     }
@@ -478,7 +478,7 @@ public static function DAYOFMONTH($dateValue = 1)
      *
      * @return array|int|string Day of the week value
      */
-    public static function WEEKDAY($dateValue = 1, $style = 1)
+    public static function WEEKDAY($dateValue = 1, $style = 1): string|int|array
     {
         return DateTimeExcel\Week::day($dateValue, $style);
     }
@@ -689,7 +689,7 @@ public static function WEEKDAY($dateValue = 1, $style = 1)
      *
      * @return array|int|string Week Number
      */
-    public static function WEEKNUM($dateValue = 1, $method = /** @scrutinizer ignore-deprecated */ self::STARTWEEK_SUNDAY)
+    public static function WEEKNUM($dateValue = 1, $method = /** @scrutinizer ignore-deprecated */ self::STARTWEEK_SUNDAY): int|string|array
     {
         return DateTimeExcel\Week::number($dateValue, $method);
     }
@@ -711,7 +711,7 @@ public static function WEEKNUM($dateValue = 1, $method = /** @scrutinizer ignore
      *
      * @return array|int|string Week Number
      */
-    public static function ISOWEEKNUM($dateValue = 1)
+    public static function ISOWEEKNUM($dateValue = 1): int|string|array
     {
         return DateTimeExcel\Week::isoWeekNumber($dateValue);
     }
@@ -734,7 +734,7 @@ public static function ISOWEEKNUM($dateValue = 1)
      *
      * @return array|int|string Month of the year
      */
-    public static function MONTHOFYEAR($dateValue = 1)
+    public static function MONTHOFYEAR($dateValue = 1): string|int|array
     {
         return DateTimeExcel\DateParts::month($dateValue);
     }
@@ -757,7 +757,7 @@ public static function MONTHOFYEAR($dateValue = 1)
      *
      * @return array|int|string Year
      */
-    public static function YEAR($dateValue = 1)
+    public static function YEAR($dateValue = 1): string|int|array
     {
         return DateTimeExcel\DateParts::year($dateValue);
     }
@@ -780,7 +780,7 @@ public static function YEAR($dateValue = 1)
      *
      * @return array|int|string Hour
      */
-    public static function HOUROFDAY($timeValue = 0)
+    public static function HOUROFDAY($timeValue = 0): string|int|array
     {
         return DateTimeExcel\TimeParts::hour($timeValue);
     }
@@ -803,7 +803,7 @@ public static function HOUROFDAY($timeValue = 0)
      *
      * @return array|int|string Minute
      */
-    public static function MINUTE($timeValue = 0)
+    public static function MINUTE($timeValue = 0): string|int|array
     {
         return DateTimeExcel\TimeParts::minute($timeValue);
     }
@@ -826,7 +826,7 @@ public static function MINUTE($timeValue = 0)
      *
      * @return array|int|string Second
      */
-    public static function SECOND($timeValue = 0)
+    public static function SECOND($timeValue = 0): string|int|array
     {
         return DateTimeExcel\TimeParts::second($timeValue);
     }
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/DateParts.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/DateParts.php
index 7bb03c9da8..c05174fa8c 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/DateParts.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/DateParts.php
@@ -28,7 +28,7 @@ class DateParts
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function day($dateValue)
+    public static function day($dateValue): array|int|string
     {
         if (is_array($dateValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $dateValue);
@@ -69,7 +69,7 @@ public static function day($dateValue)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function month($dateValue)
+    public static function month($dateValue): array|string|int
     {
         if (is_array($dateValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $dateValue);
@@ -108,7 +108,7 @@ public static function month($dateValue)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function year($dateValue)
+    public static function year($dateValue): array|string|int
     {
         if (is_array($dateValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $dateValue);
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Days360.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Days360.php
index 6f71621eaa..9ac9ccb664 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Days360.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Days360.php
@@ -44,7 +44,7 @@ class Days360
      *         If an array of values is passed for the $startDate or $endDays,arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function between($startDate = 0, $endDate = 0, $method = false)
+    public static function between($startDate = 0, $endDate = 0, $method = false): array|string|int
     {
         if (is_array($startDate) || is_array($endDate) || is_array($method)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $startDate, $endDate, $method);
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Helpers.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Helpers.php
index 238451534a..07bebe9246 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Helpers.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Helpers.php
@@ -133,10 +133,8 @@ public static function adjustYear(string $testVal1, string $testVal2, string &$t
 
     /**
      * Return result in one of three formats.
-     *
-     * @return mixed
      */
-    public static function returnIn3FormatsArray(array $dateArray, bool $noFrac = false)
+    public static function returnIn3FormatsArray(array $dateArray, bool $noFrac = false): DateTime|float|int
     {
         $retType = Functions::getReturnDateType();
         if ($retType === Functions::RETURNDATE_PHP_DATETIME_OBJECT) {
@@ -159,11 +157,11 @@ public static function returnIn3FormatsArray(array $dateArray, bool $noFrac = fa
                 $dateArray['second']
             );
         if ($retType === Functions::RETURNDATE_EXCEL) {
-            return $noFrac ? floor($excelDateValue) : (float) $excelDateValue;
+            return $noFrac ? floor($excelDateValue) : $excelDateValue;
         }
         // RETURNDATE_UNIX_TIMESTAMP)
 
-        return (int) SharedDateHelper::excelToTimestamp($excelDateValue);
+        return  SharedDateHelper::excelToTimestamp($excelDateValue);
     }
 
     /**
@@ -187,10 +185,8 @@ public static function returnIn3FormatsFloat(float $excelDateValue)
 
     /**
      * Return result in one of three formats.
-     *
-     * @return mixed
      */
-    public static function returnIn3FormatsObject(DateTime $PHPDateObject)
+    public static function returnIn3FormatsObject(DateTime $PHPDateObject): DateTime|float|int
     {
         $retType = Functions::getReturnDateType();
         if ($retType === Functions::RETURNDATE_PHP_DATETIME_OBJECT) {
@@ -203,7 +199,7 @@ public static function returnIn3FormatsObject(DateTime $PHPDateObject)
         $stamp = SharedDateHelper::PHPToExcel($PHPDateObject);
         $stamp = is_bool($stamp) ? ((int) $stamp) : $stamp;
 
-        return (int) SharedDateHelper::excelToTimestamp($stamp);
+        return SharedDateHelper::excelToTimestamp($stamp);
     }
 
     private static function baseDate(): int
@@ -238,10 +234,8 @@ public static function nullFalseTrueToNumber(&$number, bool $allowBool = true):
      * Many functions accept null argument treated as 0.
      *
      * @param mixed $number
-     *
-     * @return float|int
      */
-    public static function validateNumericNull($number)
+    public static function validateNumericNull($number): int|float
     {
         $number = Functions::flattenSingleValue($number);
         if ($number === null) {
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/NetworkDays.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/NetworkDays.php
index 3b8942bafb..a487f2a3f7 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/NetworkDays.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/NetworkDays.php
@@ -33,7 +33,7 @@ class NetworkDays
      *         If an array of values is passed for the $startDate or $endDate arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function count($startDate, $endDate, ...$dateArgs)
+    public static function count($startDate, $endDate, ...$dateArgs): array|string|int
     {
         if (is_array($startDate) || is_array($endDate)) {
             return self::evaluateArrayArgumentsSubset(
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Time.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Time.php
index 4ff71983f4..44d863006c 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Time.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Time.php
@@ -38,12 +38,12 @@ class Time
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      *
-     * @return array|mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
+     * @return array|DateTime|float|int|string Excel date/time serial value, PHP date/time serial value or PHP date/time object,
      *                        depending on the value of the ReturnDateType flag
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function fromHMS($hour, $minute, $second)
+    public static function fromHMS($hour, $minute, $second): array|string|float|int|DateTime
     {
         if (is_array($hour) || is_array($minute) || is_array($second)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $hour, $minute, $second);
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeParts.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeParts.php
index e1331b0109..1c65a6edb8 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeParts.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeParts.php
@@ -27,7 +27,7 @@ class TimeParts
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function hour($timeValue)
+    public static function hour($timeValue): array|string|int
     {
         if (is_array($timeValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $timeValue);
@@ -68,7 +68,7 @@ public static function hour($timeValue)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function minute($timeValue)
+    public static function minute($timeValue): array|string|int
     {
         if (is_array($timeValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $timeValue);
@@ -109,7 +109,7 @@ public static function minute($timeValue)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function second($timeValue)
+    public static function second($timeValue): array|string|int
     {
         if (is_array($timeValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $timeValue);
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeValue.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeValue.php
index 78d67b837d..b5024d1731 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeValue.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/TimeValue.php
@@ -31,12 +31,12 @@ class TimeValue
      *                                    Date information in time_text is ignored.
      *                         Or can be an array of date/time values
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
+     * @return array|Datetime|float|int|string Excel date/time serial value, PHP date/time serial value or PHP date/time object,
      *                        depending on the value of the ReturnDateType flag
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function fromString($timeValue)
+    public static function fromString($timeValue): array|string|Datetime|int|float
     {
         if (is_array($timeValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $timeValue);
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Week.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Week.php
index 2f69007d13..e023726d2a 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/Week.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/Week.php
@@ -45,7 +45,7 @@ class Week
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function number($dateValue, $method = Constants::STARTWEEK_SUNDAY)
+    public static function number($dateValue, $method = Constants::STARTWEEK_SUNDAY): array|int|string
     {
         if (is_array($dateValue) || is_array($method)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $dateValue, $method);
@@ -105,7 +105,7 @@ public static function number($dateValue, $method = Constants::STARTWEEK_SUNDAY)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isoWeekNumber($dateValue)
+    public static function isoWeekNumber($dateValue): array|int|string
     {
         if (is_array($dateValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $dateValue);
@@ -150,7 +150,7 @@ public static function isoWeekNumber($dateValue)
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function day($dateValue, $style = 1)
+    public static function day($dateValue, $style = 1): array|string|int
     {
         if (is_array($dateValue) || is_array($style)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $dateValue, $style);
diff --git a/src/PhpSpreadsheet/Calculation/DateTimeExcel/YearFrac.php b/src/PhpSpreadsheet/Calculation/DateTimeExcel/YearFrac.php
index 394c6b7320..d6f66a53e8 100644
--- a/src/PhpSpreadsheet/Calculation/DateTimeExcel/YearFrac.php
+++ b/src/PhpSpreadsheet/Calculation/DateTimeExcel/YearFrac.php
@@ -43,7 +43,7 @@ class YearFrac
      *         If an array of values is passed for the $startDate or $endDays,arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function fraction($startDate, $endDate, $method = 0)
+    public static function fraction($startDate, $endDate, $method = 0): array|string|int|float
     {
         if (is_array($startDate) || is_array($endDate) || is_array($method)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $startDate, $endDate, $method);
diff --git a/src/PhpSpreadsheet/Calculation/Engine/ArrayArgumentHelper.php b/src/PhpSpreadsheet/Calculation/Engine/ArrayArgumentHelper.php
index fae9d90097..1d8b329981 100644
--- a/src/PhpSpreadsheet/Calculation/Engine/ArrayArgumentHelper.php
+++ b/src/PhpSpreadsheet/Calculation/Engine/ArrayArgumentHelper.php
@@ -152,7 +152,7 @@ public function columnCount(int $argument): int
     private function rows(array $arguments): array
     {
         return array_map(
-            function ($argument) {
+            function ($argument): int {
                 return is_countable($argument) ? count($argument) : 1;
             },
             $arguments
@@ -162,7 +162,7 @@ function ($argument) {
     private function columns(array $arguments): array
     {
         return array_map(
-            function ($argument) {
+            function ($argument): int {
                 return is_array($argument) && is_array($argument[array_keys($argument)[0]])
                     ? count($argument[array_keys($argument)[0]])
                     : 1;
@@ -201,7 +201,7 @@ private function filterArray(array $array): array
     {
         return array_filter(
             $array,
-            function ($value) {
+            function ($value): bool {
                 return $value > 1;
             }
         );
diff --git a/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php b/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php
index 9cd767e6a6..09a1a251d0 100644
--- a/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php
+++ b/src/PhpSpreadsheet/Calculation/Engine/BranchPruner.php
@@ -6,10 +6,7 @@
 
 class BranchPruner
 {
-    /**
-     * @var bool
-     */
-    protected $branchPruningEnabled = true;
+    protected bool $branchPruningEnabled;
 
     /**
      * Used to generate unique store keys.
@@ -50,20 +47,11 @@ class BranchPruner
      */
     protected $braceDepthMap = [];
 
-    /**
-     * @var null|string
-     */
-    protected $currentCondition;
+    protected ?string $currentCondition = null;
 
-    /**
-     * @var null|string
-     */
-    protected $currentOnlyIf;
+    protected ?string $currentOnlyIf = null;
 
-    /**
-     * @var null|string
-     */
-    protected $currentOnlyIfNot;
+    protected ?string $currentOnlyIfNot = null;
 
     /**
      * @var null|string
diff --git a/src/PhpSpreadsheet/Calculation/Engine/CyclicReferenceStack.php b/src/PhpSpreadsheet/Calculation/Engine/CyclicReferenceStack.php
index b688e05634..6c4d23ad4c 100644
--- a/src/PhpSpreadsheet/Calculation/Engine/CyclicReferenceStack.php
+++ b/src/PhpSpreadsheet/Calculation/Engine/CyclicReferenceStack.php
@@ -13,10 +13,8 @@ class CyclicReferenceStack
 
     /**
      * Return the number of entries on the stack.
-     *
-     * @return int
      */
-    public function count()
+    public function count(): int
     {
         return count($this->stack);
     }
@@ -45,10 +43,8 @@ public function pop()
      * Test to see if a specified entry exists on the stack.
      *
      * @param mixed $value The value to test
-     *
-     * @return bool
      */
-    public function onStack($value)
+    public function onStack($value): bool
     {
         return isset($this->stack[$value]);
     }
diff --git a/src/PhpSpreadsheet/Calculation/Engine/Logger.php b/src/PhpSpreadsheet/Calculation/Engine/Logger.php
index 256c3effb1..d65bd49f7e 100644
--- a/src/PhpSpreadsheet/Calculation/Engine/Logger.php
+++ b/src/PhpSpreadsheet/Calculation/Engine/Logger.php
@@ -32,10 +32,8 @@ class Logger
 
     /**
      * The calculation engine cell reference stack.
-     *
-     * @var CyclicReferenceStack
      */
-    private $cellStack;
+    private CyclicReferenceStack $cellStack;
 
     /**
      * Instantiate a Calculation engine logger.
diff --git a/src/PhpSpreadsheet/Calculation/Engineering.php b/src/PhpSpreadsheet/Calculation/Engineering.php
index 2fcee2e02c..bf9f2f0c3a 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering.php
@@ -240,10 +240,8 @@ public static function BINTOOCT($x, $places = null)
      *                                If places is not an integer, it is truncated.
      *                                If places is nonnumeric, DEC2BIN returns the #VALUE! error value.
      *                                If places is zero or negative, DEC2BIN returns the #NUM! error value.
-     *
-     * @return array|string
      */
-    public static function DECTOBIN($x, $places = null)
+    public static function DECTOBIN($x, $places = null): string|array
     {
         return Engineering\ConvertDecimal::toBinary($x, $places);
     }
@@ -276,10 +274,8 @@ public static function DECTOBIN($x, $places = null)
      *                                If places is not an integer, it is truncated.
      *                                If places is nonnumeric, DEC2HEX returns the #VALUE! error value.
      *                                If places is zero or negative, DEC2HEX returns the #NUM! error value.
-     *
-     * @return array|string
      */
-    public static function DECTOHEX($x, $places = null)
+    public static function DECTOHEX($x, $places = null): string|array
     {
         return Engineering\ConvertDecimal::toHex($x, $places);
     }
@@ -312,10 +308,8 @@ public static function DECTOHEX($x, $places = null)
      *                                If places is not an integer, it is truncated.
      *                                If places is nonnumeric, DEC2OCT returns the #VALUE! error value.
      *                                If places is zero or negative, DEC2OCT returns the #NUM! error value.
-     *
-     * @return array|string
      */
-    public static function DECTOOCT($x, $places = null)
+    public static function DECTOOCT($x, $places = null): string|array
     {
         return Engineering\ConvertDecimal::toOctal($x, $places);
     }
@@ -521,10 +515,8 @@ public static function OCTTODEC($x)
      *                                    If places is not an integer, it is truncated.
      *                                    If places is nonnumeric, OCT2HEX returns the #VALUE! error value.
      *                                    If places is negative, OCT2HEX returns the #NUM! error value.
-     *
-     * @return array|string
      */
-    public static function OCTTOHEX($x, $places = null)
+    public static function OCTTOHEX($x, $places = null): string|array
     {
         return Engineering\ConvertOctal::toHex($x, $places);
     }
@@ -567,10 +559,8 @@ public static function COMPLEX($realNumber = 0.0, $imaginary = 0.0, $suffix = 'i
      *
      * @param string $complexNumber the complex number for which you want the imaginary
      *                                         coefficient
-     *
-     * @return array|float|string
      */
-    public static function IMAGINARY($complexNumber)
+    public static function IMAGINARY($complexNumber): string|float|array
     {
         return Engineering\Complex::IMAGINARY($complexNumber);
     }
@@ -588,10 +578,8 @@ public static function IMAGINARY($complexNumber)
      * @see Engineering\Complex::IMREAL()
      *
      * @param string $complexNumber the complex number for which you want the real coefficient
-     *
-     * @return array|float|string
      */
-    public static function IMREAL($complexNumber)
+    public static function IMREAL($complexNumber): string|float|array
     {
         return Engineering\Complex::IMREAL($complexNumber);
     }
@@ -1054,10 +1042,8 @@ public static function IMSUB($complexNumber1, $complexNumber2)
      * @see ComplexOperations::IMSUM()
      *
      * @param string ...$complexNumbers Series of complex numbers to add
-     *
-     * @return string
      */
-    public static function IMSUM(...$complexNumbers)
+    public static function IMSUM(...$complexNumbers): string
     {
         return ComplexOperations::IMSUM(...$complexNumbers);
     }
@@ -1075,10 +1061,8 @@ public static function IMSUM(...$complexNumbers)
      * @see ComplexOperations::IMPRODUCT()
      *
      * @param string ...$complexNumbers Series of complex numbers to multiply
-     *
-     * @return string
      */
-    public static function IMPRODUCT(...$complexNumbers)
+    public static function IMPRODUCT(...$complexNumbers): string
     {
         return ComplexOperations::IMPRODUCT(...$complexNumbers);
     }
@@ -1262,10 +1246,8 @@ public static function BITRSHIFT($number, $shiftAmount)
      * @param float $lower lower bound for integrating ERF
      * @param float $upper upper bound for integrating ERF.
      *                                If omitted, ERF integrates between zero and lower_limit
-     *
-     * @return array|float|string
      */
-    public static function ERF($lower, $upper = null)
+    public static function ERF($lower, $upper = null): float|string|array
     {
         return Engineering\Erf::ERF($lower, $upper);
     }
@@ -1324,10 +1306,8 @@ public static function ERFC($x)
      * @deprecated 1.16.0
      *      Use the getConversionCategories() method in the Engineering\ConvertUOM class instead
      * @see Engineering\ConvertUOM::getConversionCategories()
-     *
-     * @return array
      */
-    public static function getConversionGroups()
+    public static function getConversionGroups(): array
     {
         return Engineering\ConvertUOM::getConversionCategories();
     }
@@ -1341,10 +1321,8 @@ public static function getConversionGroups()
      * @see Engineering\ConvertUOM::getConversionCategoryUnits()
      *
      * @param null|mixed $category
-     *
-     * @return array
      */
-    public static function getConversionGroupUnits($category = null)
+    public static function getConversionGroupUnits($category = null): array
     {
         return Engineering\ConvertUOM::getConversionCategoryUnits($category);
     }
@@ -1357,10 +1335,8 @@ public static function getConversionGroupUnits($category = null)
      * @see Engineering\ConvertUOM::getConversionCategoryUnitDetails()
      *
      * @param null|mixed $category
-     *
-     * @return array
      */
-    public static function getConversionGroupUnitDetails($category = null)
+    public static function getConversionGroupUnitDetails($category = null): array
     {
         return Engineering\ConvertUOM::getConversionCategoryUnitDetails($category);
     }
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/BesselI.php b/src/PhpSpreadsheet/Calculation/Engineering/BesselI.php
index 1134574e4f..c95e46e96f 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/BesselI.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/BesselI.php
@@ -35,7 +35,7 @@ class BesselI
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BESSELI($x, $ord)
+    public static function BESSELI($x, $ord): array|string|float
     {
         if (is_array($x) || is_array($ord)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $x, $ord);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/BesselJ.php b/src/PhpSpreadsheet/Calculation/Engineering/BesselJ.php
index 457c74d6ad..e49a1b4388 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/BesselJ.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/BesselJ.php
@@ -34,7 +34,7 @@ class BesselJ
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BESSELJ($x, $ord)
+    public static function BESSELJ($x, $ord): array|string|float
     {
         if (is_array($x) || is_array($ord)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $x, $ord);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/BesselK.php b/src/PhpSpreadsheet/Calculation/Engineering/BesselK.php
index 9829f95245..9ae4aceb3e 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/BesselK.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/BesselK.php
@@ -32,7 +32,7 @@ class BesselK
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BESSELK($x, $ord)
+    public static function BESSELK($x, $ord): array|string|float
     {
         if (is_array($x) || is_array($ord)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $x, $ord);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/BesselY.php b/src/PhpSpreadsheet/Calculation/Engineering/BesselY.php
index 31d9694a70..52dc279313 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/BesselY.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/BesselY.php
@@ -31,7 +31,7 @@ class BesselY
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BESSELY($x, $ord)
+    public static function BESSELY($x, $ord): array|string|float
     {
         if (is_array($x) || is_array($ord)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $x, $ord);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/BitWise.php b/src/PhpSpreadsheet/Calculation/Engineering/BitWise.php
index fbf574dba8..db2013a12a 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/BitWise.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/BitWise.php
@@ -41,7 +41,7 @@ private static function splitNumber($number): array
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BITAND($number1, $number2)
+    public static function BITAND($number1, $number2): array|string|int
     {
         if (is_array($number1) || is_array($number2)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number1, $number2);
@@ -76,7 +76,7 @@ public static function BITAND($number1, $number2)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BITOR($number1, $number2)
+    public static function BITOR($number1, $number2): array|string|int
     {
         if (is_array($number1) || is_array($number2)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number1, $number2);
@@ -112,7 +112,7 @@ public static function BITOR($number1, $number2)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BITXOR($number1, $number2)
+    public static function BITXOR($number1, $number2): array|string|int
     {
         if (is_array($number1) || is_array($number2)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number1, $number2);
@@ -144,11 +144,11 @@ public static function BITXOR($number1, $number2)
      * @param array|int $shiftAmount
      *                      Or can be an array of values
      *
-     * @return array|float|int|string
+     * @return array|float|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BITLSHIFT($number, $shiftAmount)
+    public static function BITLSHIFT($number, $shiftAmount): array|string|float
     {
         if (is_array($number) || is_array($shiftAmount)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $shiftAmount);
@@ -182,11 +182,11 @@ public static function BITLSHIFT($number, $shiftAmount)
      * @param array|int $shiftAmount
      *                      Or can be an array of values
      *
-     * @return array|float|int|string
+     * @return array|float|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function BITRSHIFT($number, $shiftAmount)
+    public static function BITRSHIFT($number, $shiftAmount): array|string|float
     {
         if (is_array($number) || is_array($shiftAmount)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $shiftAmount);
@@ -211,10 +211,8 @@ public static function BITRSHIFT($number, $shiftAmount)
      * Validate arguments passed to the bitwise functions.
      *
      * @param mixed $value
-     *
-     * @return float
      */
-    private static function validateBitwiseArgument($value)
+    private static function validateBitwiseArgument($value): float
     {
         $value = self::nullFalseTrueToNumber($value);
 
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/Compare.php b/src/PhpSpreadsheet/Calculation/Engineering/Compare.php
index 6aaf1faa5b..0a8c1f3b44 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/Compare.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/Compare.php
@@ -29,7 +29,7 @@ class Compare
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function DELTA($a, $b = 0.0)
+    public static function DELTA($a, $b = 0.0): array|string|int
     {
         if (is_array($a) || is_array($b)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $a, $b);
@@ -64,7 +64,7 @@ public static function DELTA($a, $b = 0.0)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function GESTEP($number, $step = 0.0)
+    public static function GESTEP($number, $step = 0.0): array|string|int
     {
         if (is_array($number) || is_array($step)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $step);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/Complex.php b/src/PhpSpreadsheet/Calculation/Engineering/Complex.php
index f7ec02d43c..58b4119445 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/Complex.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/Complex.php
@@ -32,7 +32,7 @@ class Complex
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function COMPLEX($realNumber = 0.0, $imaginary = 0.0, $suffix = 'i')
+    public static function COMPLEX($realNumber = 0.0, $imaginary = 0.0, $suffix = 'i'): array|string
     {
         if (is_array($realNumber) || is_array($imaginary) || is_array($suffix)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $realNumber, $imaginary, $suffix);
@@ -74,7 +74,7 @@ public static function COMPLEX($realNumber = 0.0, $imaginary = 0.0, $suffix = 'i
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMAGINARY($complexNumber)
+    public static function IMAGINARY($complexNumber): array|string|float
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -104,7 +104,7 @@ public static function IMAGINARY($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMREAL($complexNumber)
+    public static function IMREAL($complexNumber): array|string|float
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ComplexFunctions.php b/src/PhpSpreadsheet/Calculation/Engineering/ComplexFunctions.php
index 28a27a0317..a7caa6b0b6 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ComplexFunctions.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ComplexFunctions.php
@@ -91,7 +91,7 @@ public static function IMARGUMENT($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMCONJUGATE($complexNumber)
+    public static function IMCONJUGATE($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -117,11 +117,11 @@ public static function IMCONJUGATE($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the cosine
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMCOS($complexNumber)
+    public static function IMCOS($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -147,11 +147,11 @@ public static function IMCOS($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the hyperbolic cosine
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMCOSH($complexNumber)
+    public static function IMCOSH($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -177,11 +177,11 @@ public static function IMCOSH($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the cotangent
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMCOT($complexNumber)
+    public static function IMCOT($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -207,11 +207,11 @@ public static function IMCOT($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the cosecant
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMCSC($complexNumber)
+    public static function IMCSC($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -237,11 +237,11 @@ public static function IMCSC($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the hyperbolic cosecant
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMCSCH($complexNumber)
+    public static function IMCSCH($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -267,11 +267,11 @@ public static function IMCSCH($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the sine
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMSIN($complexNumber)
+    public static function IMSIN($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -297,11 +297,11 @@ public static function IMSIN($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the hyperbolic sine
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMSINH($complexNumber)
+    public static function IMSINH($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -327,11 +327,11 @@ public static function IMSINH($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the secant
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMSEC($complexNumber)
+    public static function IMSEC($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -357,11 +357,11 @@ public static function IMSEC($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the hyperbolic secant
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMSECH($complexNumber)
+    public static function IMSECH($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -387,11 +387,11 @@ public static function IMSECH($complexNumber)
      * @param array|string $complexNumber the complex number for which you want the tangent
      *                      Or can be an array of values
      *
-     * @return array|float|string
+     * @return array|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMTAN($complexNumber)
+    public static function IMTAN($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -421,7 +421,7 @@ public static function IMTAN($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMSQRT($complexNumber)
+    public static function IMSQRT($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -456,7 +456,7 @@ public static function IMSQRT($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMLN($complexNumber)
+    public static function IMLN($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -490,7 +490,7 @@ public static function IMLN($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMLOG10($complexNumber)
+    public static function IMLOG10($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -524,7 +524,7 @@ public static function IMLOG10($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMLOG2($complexNumber)
+    public static function IMLOG2($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -558,7 +558,7 @@ public static function IMLOG2($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMEXP($complexNumber)
+    public static function IMEXP($complexNumber): array|string
     {
         if (is_array($complexNumber)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $complexNumber);
@@ -590,7 +590,7 @@ public static function IMEXP($complexNumber)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMPOWER($complexNumber, $realNumber)
+    public static function IMPOWER($complexNumber, $realNumber): array|string
     {
         if (is_array($complexNumber) || is_array($realNumber)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $complexNumber, $realNumber);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ComplexOperations.php b/src/PhpSpreadsheet/Calculation/Engineering/ComplexOperations.php
index e525b4b9aa..79c62d0966 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ComplexOperations.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ComplexOperations.php
@@ -29,7 +29,7 @@ class ComplexOperations
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMDIV($complexDividend, $complexDivisor)
+    public static function IMDIV($complexDividend, $complexDivisor): array|string
     {
         if (is_array($complexDividend) || is_array($complexDivisor)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $complexDividend, $complexDivisor);
@@ -59,7 +59,7 @@ public static function IMDIV($complexDividend, $complexDivisor)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function IMSUB($complexNumber1, $complexNumber2)
+    public static function IMSUB($complexNumber1, $complexNumber2): array|string
     {
         if (is_array($complexNumber1) || is_array($complexNumber2)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $complexNumber1, $complexNumber2);
@@ -81,10 +81,8 @@ public static function IMSUB($complexNumber1, $complexNumber2)
      *        IMSUM(complexNumber[,complexNumber[,...]])
      *
      * @param string ...$complexNumbers Series of complex numbers to add
-     *
-     * @return string
      */
-    public static function IMSUM(...$complexNumbers)
+    public static function IMSUM(...$complexNumbers): string
     {
         // Return value
         $returnValue = new ComplexObject(0.0);
@@ -111,10 +109,8 @@ public static function IMSUM(...$complexNumbers)
      *        IMPRODUCT(complexNumber[,complexNumber[,...]])
      *
      * @param string ...$complexNumbers Series of complex numbers to multiply
-     *
-     * @return string
      */
-    public static function IMPRODUCT(...$complexNumbers)
+    public static function IMPRODUCT(...$complexNumbers): string
     {
         // Return value
         $returnValue = new ComplexObject(1.0);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertBinary.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertBinary.php
index 04bf3e5060..f21b4d5a3e 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertBinary.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertBinary.php
@@ -77,7 +77,7 @@ public static function toDecimal($value)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toHex($value, $places = null)
+    public static function toHex($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
@@ -130,7 +130,7 @@ public static function toHex($value, $places = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toOctal($value, $places = null)
+    public static function toOctal($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertDecimal.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertDecimal.php
index 9b59d3995f..14ee68795f 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertDecimal.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertDecimal.php
@@ -45,7 +45,7 @@ class ConvertDecimal extends ConvertBase
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toBinary($value, $places = null)
+    public static function toBinary($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
@@ -102,7 +102,7 @@ public static function toBinary($value, $places = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toHex($value, $places = null)
+    public static function toHex($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
@@ -178,7 +178,7 @@ public static function hex32bit(float $value, string $hexstr, bool $force = fals
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toOctal($value, $places = null)
+    public static function toOctal($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php
index 55ce209ecd..9d39acfbce 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertHex.php
@@ -38,7 +38,7 @@ class ConvertHex extends ConvertBase
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toBinary($value, $places = null)
+    public static function toBinary($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
@@ -145,7 +145,7 @@ public static function toDecimal($value)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toOctal($value, $places = null)
+    public static function toOctal($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php
index add7aba01b..8436a63ef6 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertOctal.php
@@ -44,7 +44,7 @@ class ConvertOctal extends ConvertBase
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toBinary($value, $places = null)
+    public static function toBinary($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
@@ -142,7 +142,7 @@ public static function toDecimal($value)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toHex($value, $places = null)
+    public static function toHex($value, $places = null): array|string
     {
         if (is_array($value) || is_array($places)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $places);
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ConvertUOM.php b/src/PhpSpreadsheet/Calculation/Engineering/ConvertUOM.php
index 32ef9d3c77..87ea44881d 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ConvertUOM.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ConvertUOM.php
@@ -435,10 +435,8 @@ class ConvertUOM
     /**
      *    getConversionGroups
      * Returns a list of the different conversion groups for UOM conversions.
-     *
-     * @return array
      */
-    public static function getConversionCategories()
+    public static function getConversionCategories(): array
     {
         $conversionGroups = [];
         foreach (self::$conversionUnits as $conversionUnit) {
@@ -453,10 +451,8 @@ public static function getConversionCategories()
      * Returns an array of units of measure, for a specified conversion group, or for all groups.
      *
      * @param string $category The group whose units of measure you want to retrieve
-     *
-     * @return array
      */
-    public static function getConversionCategoryUnits($category = null)
+    public static function getConversionCategoryUnits($category = null): array
     {
         $conversionGroups = [];
         foreach (self::$conversionUnits as $conversionUnit => $conversionGroup) {
@@ -472,10 +468,8 @@ public static function getConversionCategoryUnits($category = null)
      * getConversionGroupUnitDetails.
      *
      * @param string $category The group whose units of measure you want to retrieve
-     *
-     * @return array
      */
-    public static function getConversionCategoryUnitDetails($category = null)
+    public static function getConversionCategoryUnitDetails($category = null): array
     {
         $conversionGroups = [];
         foreach (self::$conversionUnits as $conversionUnit => $conversionGroup) {
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/Erf.php b/src/PhpSpreadsheet/Calculation/Engineering/Erf.php
index dfd473db03..7df276b241 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/Erf.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/Erf.php
@@ -35,7 +35,7 @@ class Erf
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function ERF($lower, $upper = null)
+    public static function ERF($lower, $upper = null): array|float|string
     {
         if (is_array($lower) || is_array($upper)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $lower, $upper);
@@ -87,10 +87,8 @@ private static function makeFloat($value): float
      * Method to calculate the erf value.
      *
      * @param float|int|string $value
-     *
-     * @return float
      */
-    public static function erfValue($value)
+    public static function erfValue($value): float
     {
         $value = (float) $value;
         if (abs($value) > 2.2) {
diff --git a/src/PhpSpreadsheet/Calculation/Engineering/ErfC.php b/src/PhpSpreadsheet/Calculation/Engineering/ErfC.php
index 0350c9c640..4c2d461eef 100644
--- a/src/PhpSpreadsheet/Calculation/Engineering/ErfC.php
+++ b/src/PhpSpreadsheet/Calculation/Engineering/ErfC.php
@@ -52,7 +52,7 @@ public static function ERFC($value)
      *
      * @return float
      */
-    private static function erfcValue($value)
+    private static function erfcValue($value): float|int
     {
         $value = (float) $value;
         if (abs($value) < 2.2) {
diff --git a/src/PhpSpreadsheet/Calculation/Exception.php b/src/PhpSpreadsheet/Calculation/Exception.php
index a95a452d07..ea893d6986 100644
--- a/src/PhpSpreadsheet/Calculation/Exception.php
+++ b/src/PhpSpreadsheet/Calculation/Exception.php
@@ -10,14 +10,8 @@ class Exception extends PhpSpreadsheetException
 
     /**
      * Error handler callback.
-     *
-     * @param mixed $code
-     * @param mixed $string
-     * @param mixed $file
-     * @param mixed $line
-     * @param mixed $context
      */
-    public static function errorHandlerCallback($code, $string, $file, $line, /** @scrutinizer ignore-unused */ $context): void
+    public static function errorHandlerCallback(int $code, string $string, string $file, int $line): void
     {
         $e = new self($string, $code);
         $e->line = $line;
diff --git a/src/PhpSpreadsheet/Calculation/Financial.php b/src/PhpSpreadsheet/Calculation/Financial.php
index dcca5f8802..d447f84040 100644
--- a/src/PhpSpreadsheet/Calculation/Financial.php
+++ b/src/PhpSpreadsheet/Calculation/Financial.php
@@ -319,10 +319,9 @@ public static function COUPDAYSNC($settlement, $maturity, $frequency, $basis = 0
      *                                        3                Actual/365
      *                                        4                European 30/360
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
-     *                        depending on the value of the ReturnDateType flag
+     * @return float|string Excel date/time serial value or error message
      */
-    public static function COUPNCD($settlement, $maturity, $frequency, $basis = 0)
+    public static function COUPNCD($settlement, $maturity, $frequency, $basis = 0): string|float
     {
         return Coupons::COUPNCD($settlement, $maturity, $frequency, $basis);
     }
@@ -393,10 +392,9 @@ public static function COUPNUM($settlement, $maturity, $frequency, $basis = 0)
      *                                        3                Actual/365
      *                                        4                European 30/360
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
-     *                        depending on the value of the ReturnDateType flag
+     * @return float|string Excel date/time serial value or error message
      */
-    public static function COUPPCD($settlement, $maturity, $frequency, $basis = 0)
+    public static function COUPPCD($settlement, $maturity, $frequency, $basis = 0): string|float
     {
         return Coupons::COUPPCD($settlement, $maturity, $frequency, $basis);
     }
@@ -573,10 +571,8 @@ public static function DISC($settlement, $maturity, $price, $redemption, $basis
      *
      * @param array|float $fractional_dollar Fractional Dollar
      * @param array|int $fraction Fraction
-     *
-     * @return array|float|string
      */
-    public static function DOLLARDE($fractional_dollar = null, $fraction = 0)
+    public static function DOLLARDE($fractional_dollar = null, $fraction = 0): string|float|array
     {
         return Dollar::decimal($fractional_dollar, $fraction);
     }
@@ -597,10 +593,8 @@ public static function DOLLARDE($fractional_dollar = null, $fraction = 0)
      *
      * @param array|float $decimal_dollar Decimal Dollar
      * @param array|int $fraction Fraction
-     *
-     * @return array|float|string
      */
-    public static function DOLLARFR($decimal_dollar = null, $fraction = 0)
+    public static function DOLLARFR($decimal_dollar = null, $fraction = 0): string|float|array
     {
         return Dollar::fractional($decimal_dollar, $fraction);
     }
@@ -620,10 +614,8 @@ public static function DOLLARFR($decimal_dollar = null, $fraction = 0)
      *
      * @param float $nominalRate Nominal interest rate
      * @param int $periodsPerYear Number of compounding payments per year
-     *
-     * @return float|string
      */
-    public static function EFFECT($nominalRate = 0, $periodsPerYear = 0)
+    public static function EFFECT($nominalRate = 0, $periodsPerYear = 0): string|float
     {
         return Financial\InterestRate::effective($nominalRate, $periodsPerYear);
     }
@@ -650,10 +642,8 @@ public static function EFFECT($nominalRate = 0, $periodsPerYear = 0)
      * @param int $type A number 0 or 1 and indicates when payments are due:
      *                                0 or omitted    At the end of the period.
      *                                1                At the beginning of the period.
-     *
-     * @return float|string
      */
-    public static function FV($rate = 0, $nper = 0, $pmt = 0, $pv = 0, $type = 0)
+    public static function FV($rate = 0, $nper = 0, $pmt = 0, $pv = 0, $type = 0): string|float
     {
         return Financial\CashFlow\Constant\Periodic::futureValue($rate, $nper, $pmt, $pv, $type);
     }
@@ -733,10 +723,8 @@ public static function INTRATE($settlement, $maturity, $investment, $redemption,
      * @param float $pv Present Value
      * @param float $fv Future Value
      * @param int $type Payment type: 0 = at the end of each period, 1 = at the beginning of each period
-     *
-     * @return float|string
      */
-    public static function IPMT($rate, $per, $nper, $pv, $fv = 0, $type = 0)
+    public static function IPMT($rate, $per, $nper, $pv, $fv = 0, $type = 0): string|float
     {
         return Financial\CashFlow\Constant\Periodic\Interest::payment($rate, $per, $nper, $pv, $fv, $type);
     }
@@ -842,7 +830,7 @@ public static function MIRR($values, $finance_rate, $reinvestment_rate)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function NOMINAL($effectiveRate = 0, $periodsPerYear = 0)
+    public static function NOMINAL($effectiveRate = 0, $periodsPerYear = 0): string|float
     {
         return InterestRate::nominal($effectiveRate, $periodsPerYear);
     }
@@ -948,7 +936,7 @@ public static function PMT($rate = 0, $nper = 0, $pv = 0, $fv = 0, $type = 0)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function PPMT($rate, $per, $nper, $pv, $fv = 0, $type = 0)
+    public static function PPMT($rate, $per, $nper, $pv, $fv = 0, $type = 0): string|float
     {
         return Financial\CashFlow\Constant\Periodic\Payments::interestPayment($rate, $per, $nper, $pv, $fv, $type);
     }
@@ -983,7 +971,7 @@ public static function PPMT($rate, $per, $nper, $pv, $fv = 0, $type = 0)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function PRICE($settlement, $maturity, $rate, $yield, $redemption, $frequency, $basis = 0)
+    public static function PRICE($settlement, $maturity, $rate, $yield, $redemption, $frequency, $basis = 0): string|float
     {
         return Securities\Price::price($settlement, $maturity, $rate, $yield, $redemption, $frequency, $basis);
     }
@@ -1066,7 +1054,7 @@ public static function PRICEMAT($settlement, $maturity, $issue, $rate, $yield, $
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function PV($rate = 0, $nper = 0, $pmt = 0, $fv = 0, $type = 0)
+    public static function PV($rate = 0, $nper = 0, $pmt = 0, $fv = 0, $type = 0): string|float
     {
         return Financial\CashFlow\Constant\Periodic::presentValue($rate, $nper, $pmt, $fv, $type);
     }
@@ -1218,7 +1206,7 @@ public static function SYD($cost, $salvage, $life, $period)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function TBILLEQ($settlement, $maturity, $discount)
+    public static function TBILLEQ($settlement, $maturity, $discount): string|float
     {
         return TreasuryBill::bondEquivalentYield($settlement, $maturity, $discount);
     }
@@ -1241,7 +1229,7 @@ public static function TBILLEQ($settlement, $maturity, $discount)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function TBILLPRICE($settlement, $maturity, $discount)
+    public static function TBILLPRICE($settlement, $maturity, $discount): string|float
     {
         return TreasuryBill::price($settlement, $maturity, $discount);
     }
@@ -1261,10 +1249,8 @@ public static function TBILLPRICE($settlement, $maturity, $discount)
      * @param mixed $maturity The Treasury bill's maturity date.
      *                                The maturity date is the date when the Treasury bill expires.
      * @param mixed $price The Treasury bill's price per $100 face value
-     *
-     * @return float|mixed|string
      */
-    public static function TBILLYIELD($settlement, $maturity, $price)
+    public static function TBILLYIELD($settlement, $maturity, $price): string|float
     {
         return TreasuryBill::yield($settlement, $maturity, $price);
     }
@@ -1290,7 +1276,7 @@ public static function TBILLYIELD($settlement, $maturity, $price)
      *
      * @return float|mixed|string
      */
-    public static function XIRR($values, $dates, $guess = 0.1)
+    public static function XIRR(array $values, array $dates, $guess = 0.1)
     {
         return Financial\CashFlow\Variable\NonPeriodic::rate($values, $dates, $guess);
     }
diff --git a/src/PhpSpreadsheet/Calculation/Financial/Amortization.php b/src/PhpSpreadsheet/Calculation/Financial/Amortization.php
index 72a71b295e..37a9746cb8 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/Amortization.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/Amortization.php
@@ -47,7 +47,7 @@ public static function AMORDEGRC(
         $period,
         $rate,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|float {
         $cost = Functions::flattenSingleValue($cost);
         $purchased = Functions::flattenSingleValue($purchased);
         $firstPeriod = Functions::flattenSingleValue($firstPeriod);
@@ -136,7 +136,7 @@ public static function AMORLINC(
         $period,
         $rate,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|float {
         $cost = Functions::flattenSingleValue($cost);
         $purchased = Functions::flattenSingleValue($purchased);
         $firstPeriod = Functions::flattenSingleValue($firstPeriod);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic.php
index a19c37f60f..746dd317ee 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic.php
@@ -28,8 +28,6 @@ class Periodic
      * @param mixed $type A number 0 or 1 and indicates when payments are due:
      *                      0 or omitted    At the end of the period.
      *                      1               At the beginning of the period.
-     *
-     * @return float|string
      */
     public static function futureValue(
         $rate,
@@ -37,7 +35,7 @@ public static function futureValue(
         $payment = 0.0,
         $presentValue = 0.0,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float {
         $rate = Functions::flattenSingleValue($rate);
         $numberOfPeriods = Functions::flattenSingleValue($numberOfPeriods);
         $payment = ($payment === null) ? 0.0 : Functions::flattenSingleValue($payment);
@@ -76,7 +74,7 @@ public static function presentValue(
         $payment = 0.0,
         $futureValue = 0.0,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float {
         $rate = Functions::flattenSingleValue($rate);
         $numberOfPeriods = Functions::flattenSingleValue($numberOfPeriods);
         $payment = ($payment === null) ? 0.0 : Functions::flattenSingleValue($payment);
@@ -176,16 +174,13 @@ private static function calculatePresentValue(
         return -$futureValue - $payment * $numberOfPeriods;
     }
 
-    /**
-     * @return float|string
-     */
     private static function calculatePeriods(
         float $rate,
         float $payment,
         float $presentValue,
         float $futureValue,
         int $type
-    ) {
+    ): string|float {
         if ($rate != 0.0) {
             if ($presentValue == 0.0) {
                 return ExcelError::NAN();
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Cumulative.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Cumulative.php
index b7aaffd82c..e8b9435a4c 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Cumulative.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Cumulative.php
@@ -37,7 +37,7 @@ public static function interest(
         $start,
         $end,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float|int {
         $rate = Functions::flattenSingleValue($rate);
         $periods = Functions::flattenSingleValue($periods);
         $presentValue = Functions::flattenSingleValue($presentValue);
@@ -102,7 +102,7 @@ public static function principal(
         $start,
         $end,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float|int {
         $rate = Functions::flattenSingleValue($rate);
         $periods = Functions::flattenSingleValue($periods);
         $presentValue = Functions::flattenSingleValue($presentValue);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Interest.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Interest.php
index caec74fc51..17173169cc 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Interest.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Interest.php
@@ -29,8 +29,6 @@ class Interest
      * @param mixed $presentValue Present Value
      * @param mixed $futureValue Future Value
      * @param mixed $type Payment type: 0 = at the end of each period, 1 = at the beginning of each period
-     *
-     * @return float|string
      */
     public static function payment(
         $interestRate,
@@ -39,7 +37,7 @@ public static function payment(
         $presentValue,
         $futureValue = 0,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float {
         $interestRate = Functions::flattenSingleValue($interestRate);
         $period = Functions::flattenSingleValue($period);
         $numberOfPeriods = Functions::flattenSingleValue($numberOfPeriods);
@@ -88,10 +86,8 @@ public static function payment(
      * @param mixed $period is the period to calculate the interest rate.  It must be betweeen 1 and number_payments.
      * @param mixed $numberOfPeriods is the number of payments for the annuity
      * @param mixed $principleRemaining is the loan amount or present value of the payments
-     *
-     * @return float|string
      */
-    public static function schedulePayment($interestRate, $period, $numberOfPeriods, $principleRemaining)
+    public static function schedulePayment($interestRate, $period, $numberOfPeriods, $principleRemaining): string|float
     {
         $interestRate = Functions::flattenSingleValue($interestRate);
         $period = Functions::flattenSingleValue($period);
@@ -152,8 +148,6 @@ public static function schedulePayment($interestRate, $period, $numberOfPeriods,
      *                      1               At the beginning of the period.
      * @param mixed $guess Your guess for what the rate will be.
      *                          If you omit guess, it is assumed to be 10 percent.
-     *
-     * @return float|string
      */
     public static function rate(
         $numberOfPeriods,
@@ -162,7 +156,7 @@ public static function rate(
         $futureValue = 0.0,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD,
         $guess = 0.1
-    ) {
+    ): string|float {
         $numberOfPeriods = Functions::flattenSingleValue($numberOfPeriods);
         $payment = Functions::flattenSingleValue($payment);
         $presentValue = Functions::flattenSingleValue($presentValue);
@@ -199,8 +193,7 @@ public static function rate(
         return $close ? $rate : ExcelError::NAN();
     }
 
-    /** @return float|string */
-    private static function rateNextGuess(float $rate, int $numberOfPeriods, float $payment, float $presentValue, float $futureValue, int $type)
+    private static function rateNextGuess(float $rate, int $numberOfPeriods, float $payment, float $presentValue, float $futureValue, int $type): string|float
     {
         if ($rate == 0.0) {
             return ExcelError::NAN();
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/InterestAndPrincipal.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/InterestAndPrincipal.php
index 1408d465a9..ea9abb9828 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/InterestAndPrincipal.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/InterestAndPrincipal.php
@@ -6,11 +6,9 @@
 
 class InterestAndPrincipal
 {
-    /** @var float */
-    protected $interest;
+    protected float $interest;
 
-    /** @var float */
-    protected $principal;
+    protected float $principal;
 
     public function __construct(
         float $rate = 0.0,
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Payments.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Payments.php
index 83965f9d3b..04284f4552 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Payments.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Constant/Periodic/Payments.php
@@ -29,7 +29,7 @@ public static function annuity(
         $presentValue,
         $futureValue = 0,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float {
         $interestRate = Functions::flattenSingleValue($interestRate);
         $numberOfPeriods = Functions::flattenSingleValue($numberOfPeriods);
         $presentValue = Functions::flattenSingleValue($presentValue);
@@ -77,7 +77,7 @@ public static function interestPayment(
         $presentValue,
         $futureValue = 0,
         $type = FinancialConstants::PAYMENT_END_OF_PERIOD
-    ) {
+    ): string|float {
         $interestRate = Functions::flattenSingleValue($interestRate);
         $period = Functions::flattenSingleValue($period);
         $numberOfPeriods = Functions::flattenSingleValue($numberOfPeriods);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Single.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Single.php
index 058e89c64e..30a152208f 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Single.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Single.php
@@ -19,10 +19,8 @@ class Single
      *
      * @param mixed $principal the present value
      * @param float[] $schedule an array of interest rates to apply
-     *
-     * @return float|string
      */
-    public static function futureValue($principal, $schedule)
+    public static function futureValue($principal, $schedule): string|float
     {
         $principal = Functions::flattenSingleValue($principal);
         $schedule = Functions::flattenArray($schedule);
@@ -52,7 +50,7 @@ public static function futureValue($principal, $schedule)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function periods($rate, $presentValue, $futureValue)
+    public static function periods($rate, $presentValue, $futureValue): string|float
     {
         $rate = Functions::flattenSingleValue($rate);
         $presentValue = Functions::flattenSingleValue($presentValue);
@@ -85,7 +83,7 @@ public static function periods($rate, $presentValue, $futureValue)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function interestRate($periods = 0.0, $presentValue = 0.0, $futureValue = 0.0)
+    public static function interestRate($periods = 0.0, $presentValue = 0.0, $futureValue = 0.0): string|float
     {
         $periods = Functions::flattenSingleValue($periods);
         $presentValue = Functions::flattenSingleValue($presentValue);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/NonPeriodic.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/NonPeriodic.php
index b4247b704f..4d6819eb13 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/NonPeriodic.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/NonPeriodic.php
@@ -32,7 +32,7 @@ class NonPeriodic
      *
      * @return float|string
      */
-    public static function rate($values, $dates, $guess = self::DEFAULT_GUESS)
+    public static function rate(array $values, array $dates, $guess = self::DEFAULT_GUESS)
     {
         $rslt = self::xirrPart1($values, $dates);
         if ($rslt !== '') {
@@ -182,10 +182,7 @@ private static function xirrPart2(array &$values): string
         return '';
     }
 
-    /**
-     * @return float|string
-     */
-    private static function xirrPart3(array $values, array $dates, float $x1, float $x2)
+    private static function xirrPart3(array $values, array $dates, float $x1, float $x2): float|string
     {
         $f = self::xnpvOrdered($x1, $values, $dates, false);
         if ($f < 0.0) {
@@ -214,10 +211,7 @@ private static function xirrPart3(array $values, array $dates, float $x1, float
         return $rslt;
     }
 
-    /**
-     * @return float|string
-     */
-    private static function xirrBisection(array $values, array $dates, float $x1, float $x2)
+    private static function xirrBisection(array $values, array $dates, float $x1, float $x2): string|float
     {
         $rslt = ExcelError::NAN();
         for ($i = 0; $i < self::FINANCIAL_MAX_ITERATIONS; ++$i) {
diff --git a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/Periodic.php b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/Periodic.php
index d899e8441e..c4afaf5ead 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/Periodic.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/CashFlow/Variable/Periodic.php
@@ -28,10 +28,8 @@ class Periodic
      *                                Values must contain at least one positive value and one negative value to
      *                                    calculate the internal rate of return.
      * @param mixed $guess A number that you guess is close to the result of IRR
-     *
-     * @return float|string
      */
-    public static function rate($values, $guess = 0.1)
+    public static function rate($values, $guess = 0.1): string|float
     {
         if (!is_array($values)) {
             return ExcelError::VALUE();
@@ -99,7 +97,7 @@ public static function rate($values, $guess = 0.1)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function modifiedRate($values, $financeRate, $reinvestmentRate)
+    public static function modifiedRate($values, $financeRate, $reinvestmentRate): string|float
     {
         if (!is_array($values)) {
             return ExcelError::DIV0();
@@ -148,7 +146,7 @@ public static function modifiedRate($values, $financeRate, $reinvestmentRate)
      *
      * @return float
      */
-    public static function presentValue($rate, ...$args)
+    public static function presentValue($rate, ...$args): int|float
     {
         $returnValue = 0;
 
diff --git a/src/PhpSpreadsheet/Calculation/Financial/Coupons.php b/src/PhpSpreadsheet/Calculation/Financial/Coupons.php
index 4028cd4740..88b0429370 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/Coupons.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/Coupons.php
@@ -47,7 +47,7 @@ public static function COUPDAYBS(
         $maturity,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|int|float {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $frequency = Functions::flattenSingleValue($frequency);
@@ -110,7 +110,7 @@ public static function COUPDAYS(
         $maturity,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|int|float {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $frequency = Functions::flattenSingleValue($frequency);
@@ -173,15 +173,13 @@ public static function COUPDAYS(
      *                         2               Actual/360
      *                         3               Actual/365
      *                         4               European 30/360
-     *
-     * @return float|string
      */
     public static function COUPDAYSNC(
         $settlement,
         $maturity,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|float {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $frequency = Functions::flattenSingleValue($frequency);
@@ -239,15 +237,14 @@ public static function COUPDAYSNC(
      *                         3               Actual/365
      *                         4               European 30/360
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
-     *                     depending on the value of the ReturnDateType flag
+     * @return float|string Excel date/time serial value or error message
      */
     public static function COUPNCD(
         $settlement,
         $maturity,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|float {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $frequency = Functions::flattenSingleValue($frequency);
@@ -294,15 +291,13 @@ public static function COUPNCD(
      *                         2               Actual/360
      *                         3               Actual/365
      *                         4               European 30/360
-     *
-     * @return int|string
      */
     public static function COUPNUM(
         $settlement,
         $maturity,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|int {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $frequency = Functions::flattenSingleValue($frequency);
@@ -355,15 +350,14 @@ public static function COUPNUM(
      *                         3               Actual/365
      *                         4               European 30/360
      *
-     * @return mixed Excel date/time serial value, PHP date/time serial value or PHP date/time object,
-     *                     depending on the value of the ReturnDateType flag
+     * @return float|string Excel date/time serial value or error message
      */
     public static function COUPPCD(
         $settlement,
         $maturity,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|float {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $frequency = Functions::flattenSingleValue($frequency);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/Depreciation.php b/src/PhpSpreadsheet/Calculation/Financial/Depreciation.php
index e542a869ed..f987563a33 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/Depreciation.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/Depreciation.php
@@ -36,7 +36,7 @@ class Depreciation
      *
      * @return float|string
      */
-    public static function DB($cost, $salvage, $life, $period, $month = 12)
+    public static function DB($cost, $salvage, $life, $period, $month = 12): string|float|int
     {
         $cost = Functions::flattenSingleValue($cost);
         $salvage = Functions::flattenSingleValue($salvage);
@@ -150,7 +150,7 @@ public static function DDB($cost, $salvage, $life, $period, $factor = 2.0)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function SLN($cost, $salvage, $life)
+    public static function SLN($cost, $salvage, $life): string|float
     {
         $cost = Functions::flattenSingleValue($cost);
         $salvage = Functions::flattenSingleValue($salvage);
@@ -183,7 +183,7 @@ public static function SLN($cost, $salvage, $life)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function SYD($cost, $salvage, $life, $period)
+    public static function SYD($cost, $salvage, $life, $period): string|float
     {
         $cost = Functions::flattenSingleValue($cost);
         $salvage = Functions::flattenSingleValue($salvage);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/Dollar.php b/src/PhpSpreadsheet/Calculation/Financial/Dollar.php
index b1f0d25c7b..0ae9d9f231 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/Dollar.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/Dollar.php
@@ -48,10 +48,8 @@ public static function format($number, $precision = 2)
      *              Or can be an array of values
      * @param mixed $fraction Fraction
      *              Or can be an array of values
-     *
-     * @return array|float|string
      */
-    public static function decimal($fractionalDollar = null, $fraction = 0)
+    public static function decimal($fractionalDollar = null, $fraction = 0): array|string|float
     {
         if (is_array($fractionalDollar) || is_array($fraction)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $fractionalDollar, $fraction);
@@ -96,10 +94,8 @@ public static function decimal($fractionalDollar = null, $fraction = 0)
      *              Or can be an array of values
      * @param mixed $fraction Fraction
      *              Or can be an array of values
-     *
-     * @return array|float|string
      */
-    public static function fractional($decimalDollar = null, $fraction = 0)
+    public static function fractional($decimalDollar = null, $fraction = 0): array|string|float
     {
         if (is_array($decimalDollar) || is_array($fraction)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $decimalDollar, $fraction);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/Helpers.php b/src/PhpSpreadsheet/Calculation/Financial/Helpers.php
index c7f1f46a27..aa2871295a 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/Helpers.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/Helpers.php
@@ -24,7 +24,7 @@ class Helpers
      *
      * @return int|string Result, or a string containing an error
      */
-    public static function daysPerYear($year, $basis = 0)
+    public static function daysPerYear($year, $basis = 0): string|int
     {
         if (!is_numeric($basis)) {
             return ExcelError::NAN();
diff --git a/src/PhpSpreadsheet/Calculation/Financial/InterestRate.php b/src/PhpSpreadsheet/Calculation/Financial/InterestRate.php
index 1cbe2657b5..eb48059a33 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/InterestRate.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/InterestRate.php
@@ -19,10 +19,8 @@ class InterestRate
      *
      * @param mixed $nominalRate Nominal interest rate as a float
      * @param mixed $periodsPerYear Integer number of compounding payments per year
-     *
-     * @return float|string
      */
-    public static function effective($nominalRate = 0, $periodsPerYear = 0)
+    public static function effective($nominalRate = 0, $periodsPerYear = 0): string|float
     {
         $nominalRate = Functions::flattenSingleValue($nominalRate);
         $periodsPerYear = Functions::flattenSingleValue($periodsPerYear);
@@ -51,7 +49,7 @@ public static function effective($nominalRate = 0, $periodsPerYear = 0)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function nominal($effectiveRate = 0, $periodsPerYear = 0)
+    public static function nominal($effectiveRate = 0, $periodsPerYear = 0): string|float
     {
         $effectiveRate = Functions::flattenSingleValue($effectiveRate);
         $periodsPerYear = Functions::flattenSingleValue($periodsPerYear);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/Securities/Price.php b/src/PhpSpreadsheet/Calculation/Financial/Securities/Price.php
index 22c93c0e22..7490da141c 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/Securities/Price.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/Securities/Price.php
@@ -46,7 +46,7 @@ public static function price(
         $redemption,
         $frequency,
         $basis = FinancialConstants::BASIS_DAYS_PER_YEAR_NASD
-    ) {
+    ): string|float {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
         $rate = Functions::flattenSingleValue($rate);
diff --git a/src/PhpSpreadsheet/Calculation/Financial/TreasuryBill.php b/src/PhpSpreadsheet/Calculation/Financial/TreasuryBill.php
index 7ee34f7324..c90b5225d6 100644
--- a/src/PhpSpreadsheet/Calculation/Financial/TreasuryBill.php
+++ b/src/PhpSpreadsheet/Calculation/Financial/TreasuryBill.php
@@ -24,7 +24,7 @@ class TreasuryBill
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function bondEquivalentYield($settlement, $maturity, $discount)
+    public static function bondEquivalentYield($settlement, $maturity, $discount): string|float
     {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
@@ -69,7 +69,7 @@ public static function bondEquivalentYield($settlement, $maturity, $discount)
      *
      * @return float|string Result, or a string containing an error
      */
-    public static function price($settlement, $maturity, $discount)
+    public static function price($settlement, $maturity, $discount): string|float
     {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
@@ -115,11 +115,9 @@ public static function price($settlement, $maturity, $discount)
      *                                    the Treasury bill is traded to the buyer.
      * @param mixed $maturity The Treasury bill's maturity date.
      *                                The maturity date is the date when the Treasury bill expires.
-     * @param mixed $price The Treasury bill's price per $100 face value
-     *
-     * @return float|string
+     * @param float|string $price The Treasury bill's price per $100 face value
      */
-    public static function yield($settlement, $maturity, $price)
+    public static function yield($settlement, $maturity, $price): string|float
     {
         $settlement = Functions::flattenSingleValue($settlement);
         $maturity = Functions::flattenSingleValue($maturity);
diff --git a/src/PhpSpreadsheet/Calculation/FormulaParser.php b/src/PhpSpreadsheet/Calculation/FormulaParser.php
index 14c5ae50a6..4cb4d44c36 100644
--- a/src/PhpSpreadsheet/Calculation/FormulaParser.php
+++ b/src/PhpSpreadsheet/Calculation/FormulaParser.php
@@ -46,10 +46,8 @@ class FormulaParser
 
     /**
      * Formula.
-     *
-     * @var string
      */
-    private $formula;
+    private string $formula;
 
     /**
      * Tokens.
@@ -102,10 +100,8 @@ public function getToken(int $id = 0): FormulaToken
 
     /**
      * Get Token count.
-     *
-     * @return int
      */
-    public function getTokenCount()
+    public function getTokenCount(): int
     {
         return count($this->tokens);
     }
diff --git a/src/PhpSpreadsheet/Calculation/Functions.php b/src/PhpSpreadsheet/Calculation/Functions.php
index a645d790a4..5a57d7bed3 100644
--- a/src/PhpSpreadsheet/Calculation/Functions.php
+++ b/src/PhpSpreadsheet/Calculation/Functions.php
@@ -51,7 +51,7 @@ class Functions
      *
      * @return bool (Success or Failure)
      */
-    public static function setCompatibilityMode($compatibilityMode)
+    public static function setCompatibilityMode($compatibilityMode): bool
     {
         if (
             ($compatibilityMode == self::COMPATIBILITY_EXCEL) ||
@@ -91,7 +91,7 @@ public static function getCompatibilityMode()
      *
      * @return bool Success or failure
      */
-    public static function setReturnDateType($returnDateType)
+    public static function setReturnDateType($returnDateType): bool
     {
         if (
             ($returnDateType == self::RETURNDATE_UNIX_TIMESTAMP) ||
@@ -125,7 +125,7 @@ public static function getReturnDateType()
      *
      * @return string #Not Yet Implemented
      */
-    public static function DUMMY()
+    public static function DUMMY(): string
     {
         return '#Not Yet Implemented';
     }
@@ -220,7 +220,7 @@ private static function operandSpecialHandling($operand)
      *
      * @return string #NULL!
      */
-    public static function null()
+    public static function null(): string
     {
         return Information\ExcelError::null();
     }
@@ -235,7 +235,7 @@ public static function null()
      *
      * @return string #NUM!
      */
-    public static function NAN()
+    public static function NAN(): string
     {
         return Information\ExcelError::NAN();
     }
@@ -250,7 +250,7 @@ public static function NAN()
      *
      * @return string #REF!
      */
-    public static function REF()
+    public static function REF(): string
     {
         return Information\ExcelError::REF();
     }
@@ -269,7 +269,7 @@ public static function REF()
      *
      * @return string #N/A!
      */
-    public static function NA()
+    public static function NA(): string
     {
         return Information\ExcelError::NA();
     }
@@ -284,7 +284,7 @@ public static function NA()
      *
      * @return string #VALUE!
      */
-    public static function VALUE()
+    public static function VALUE(): string
     {
         return Information\ExcelError::VALUE();
     }
@@ -299,7 +299,7 @@ public static function VALUE()
      *
      * @return string #NAME?
      */
-    public static function NAME()
+    public static function NAME(): string
     {
         return Information\ExcelError::NAME();
     }
@@ -312,7 +312,7 @@ public static function NAME()
      *
      * @return string #Not Yet Implemented
      */
-    public static function DIV0()
+    public static function DIV0(): string
     {
         return Information\ExcelError::DIV0();
     }
@@ -444,10 +444,8 @@ public static function isNumber($value = null)
      *
      * @deprecated 1.23.0 Use the isLogical() method in the Information\Value class instead
      * @see Information\Value::isLogical()
-     *
-     * @return array|bool
      */
-    public static function isLogical($value = null)
+    public static function isLogical($value = null): bool|array
     {
         return Information\Value::isLogical($value);
     }
@@ -516,7 +514,7 @@ public static function n($value = null)
      *
      * @param null|mixed $value The value you want tested
      *
-     * @return number N converts values listed in the following table
+     * @return int N converts values listed in the following table
      *        If value is or refers to N returns
      *        A number            1
      *        Text                2
@@ -524,7 +522,7 @@ public static function n($value = null)
      *        An error value        16
      *        Array or Matrix        64
      */
-    public static function TYPE($value = null)
+    public static function TYPE($value = null): int
     {
         return Information\Value::type($value);
     }
@@ -536,7 +534,7 @@ public static function TYPE($value = null)
      *
      * @return array Flattened array
      */
-    public static function flattenArray($array)
+    public static function flattenArray($array): array
     {
         if (!is_array($array)) {
             return (array) $array;
diff --git a/src/PhpSpreadsheet/Calculation/Information/ErrorValue.php b/src/PhpSpreadsheet/Calculation/Information/ErrorValue.php
index 4b9f818fe5..c247edc86c 100644
--- a/src/PhpSpreadsheet/Calculation/Information/ErrorValue.php
+++ b/src/PhpSpreadsheet/Calculation/Information/ErrorValue.php
@@ -18,7 +18,7 @@ class ErrorValue
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isErr($value = '')
+    public static function isErr($value = ''): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -37,7 +37,7 @@ public static function isErr($value = '')
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isError($value = '')
+    public static function isError($value = ''): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -60,7 +60,7 @@ public static function isError($value = '')
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isNa($value = '')
+    public static function isNa($value = ''): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
diff --git a/src/PhpSpreadsheet/Calculation/Information/ExcelError.php b/src/PhpSpreadsheet/Calculation/Information/ExcelError.php
index 06f386635c..22ae025c7d 100644
--- a/src/PhpSpreadsheet/Calculation/Information/ExcelError.php
+++ b/src/PhpSpreadsheet/Calculation/Information/ExcelError.php
@@ -53,10 +53,8 @@ public static function throwError($value): string
      * ERROR_TYPE.
      *
      * @param mixed $value Value to check
-     *
-     * @return array|int|string
      */
-    public static function type($value = '')
+    public static function type($value = ''): array|int|string
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
diff --git a/src/PhpSpreadsheet/Calculation/Information/Value.php b/src/PhpSpreadsheet/Calculation/Information/Value.php
index 341d93b984..5c35849b07 100644
--- a/src/PhpSpreadsheet/Calculation/Information/Value.php
+++ b/src/PhpSpreadsheet/Calculation/Information/Value.php
@@ -24,7 +24,7 @@ class Value
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isBlank($value = null)
+    public static function isBlank($value = null): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -37,10 +37,8 @@ public static function isBlank($value = null)
      * IS_REF.
      *
      * @param mixed $value Value to check
-     *
-     * @return bool
      */
-    public static function isRef($value, ?Cell $cell = null)
+    public static function isRef($value, ?Cell $cell = null): bool
     {
         if ($cell === null || $value === $cell->getCoordinate()) {
             return false;
@@ -52,7 +50,7 @@ public static function isRef($value, ?Cell $cell = null)
             if (!empty($worksheet) && $cell->getWorksheet()->getParentOrThrow()->getSheetByName($worksheet) === null) {
                 return false;
             }
-            [$column, $row] = Coordinate::indexesFromString($cellValue);
+            [$column, $row] = Coordinate::indexesFromString($cellValue ?? '');
             if ($column > 16384 || $row > 1048576) {
                 return false;
             }
@@ -75,7 +73,7 @@ public static function isRef($value, ?Cell $cell = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isEven($value = null)
+    public static function isEven($value = null): array|string|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -100,7 +98,7 @@ public static function isEven($value = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isOdd($value = null)
+    public static function isOdd($value = null): array|string|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -125,7 +123,7 @@ public static function isOdd($value = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isNumber($value = null)
+    public static function isNumber($value = null): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -148,7 +146,7 @@ public static function isNumber($value = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isLogical($value = null)
+    public static function isLogical($value = null): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -167,7 +165,7 @@ public static function isLogical($value = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isText($value = null)
+    public static function isText($value = null): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -186,7 +184,7 @@ public static function isText($value = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function isNonText($value = null)
+    public static function isNonText($value = null): array|bool
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -281,7 +279,7 @@ public static function asNumber($value = null)
      *
      * @param null|mixed $value The value you want tested
      *
-     * @return number N converts values listed in the following table
+     * @return int N converts values listed in the following table
      *        If value is or refers to N returns
      *        A number            1
      *        Text                2
@@ -289,7 +287,7 @@ public static function asNumber($value = null)
      *        An error value      16
      *        Array or Matrix     64
      */
-    public static function type($value = null)
+    public static function type($value = null): int
     {
         $value = Functions::flattenArrayIndexed($value);
         if (is_array($value) && (count($value) > 1)) {
diff --git a/src/PhpSpreadsheet/Calculation/Logical.php b/src/PhpSpreadsheet/Calculation/Logical.php
index 92e779e06f..e640307a67 100644
--- a/src/PhpSpreadsheet/Calculation/Logical.php
+++ b/src/PhpSpreadsheet/Calculation/Logical.php
@@ -159,7 +159,7 @@ public static function logicalXor(...$args)
      *
      * @return array|bool|string the boolean inverse of the argument
      */
-    public static function NOT($logical = false)
+    public static function NOT($logical = false): bool|string|array
     {
         return Logical\Operations::NOT($logical);
     }
diff --git a/src/PhpSpreadsheet/Calculation/Logical/Operations.php b/src/PhpSpreadsheet/Calculation/Logical/Operations.php
index f09785919c..3c9f459aa2 100644
--- a/src/PhpSpreadsheet/Calculation/Logical/Operations.php
+++ b/src/PhpSpreadsheet/Calculation/Logical/Operations.php
@@ -116,7 +116,7 @@ public static function logicalXor(...$args)
      *         If an array of values is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function NOT($logical = false)
+    public static function NOT($logical = false): array|bool|string
     {
         if (is_array($logical)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $logical);
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef.php b/src/PhpSpreadsheet/Calculation/LookupRef.php
index ce4db4d7ca..e61aefdcc3 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef.php
@@ -40,10 +40,8 @@ class LookupRef
      *                                TRUE or omitted      CELL_ADDRESS returns an A1-style reference
      *                                FALSE                CELL_ADDRESS returns an R1C1-style reference
      * @param array|string $sheetText Optional Name of worksheet to use
-     *
-     * @return array|string
      */
-    public static function cellAddress($row, $column, $relativity = 1, $referenceStyle = true, $sheetText = '')
+    public static function cellAddress($row, $column, $relativity = 1, $referenceStyle = true, $sheetText = ''): string|array
     {
         return Address::cell($row, $column, $relativity, $referenceStyle, $sheetText);
     }
@@ -268,9 +266,9 @@ public static function CHOOSE(...$chooseArgs)
      * @param mixed $matchType The number -1, 0, or 1. -1 means above, 0 means exact match, 1 means below.
      *                         If match_type is 1 or -1, the list has to be ordered.
      *
-     * @return array|int|string The relative position of the found item
+     * @return array|float|int|string The relative position of the found item
      */
-    public static function MATCH($lookupValue, $lookupArray, $matchType = 1)
+    public static function MATCH($lookupValue, $lookupArray, $matchType = 1): array|float|int|string
     {
         return LookupRef\ExcelMatch::MATCH($lookupValue, $lookupArray, $matchType);
     }
@@ -314,7 +312,7 @@ public static function INDEX($matrix, $rowNum = 0, $columnNum = 0)
      * Unlike the Excel TRANSPOSE function, which will only work on a single row or column,
      *     this function will transpose a full matrix
      */
-    public static function TRANSPOSE($matrixData)
+    public static function TRANSPOSE($matrixData): array
     {
         return Matrix::transpose($matrixData);
     }
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Address.php b/src/PhpSpreadsheet/Calculation/LookupRef/Address.php
index 1a0035d59b..28811f7e69 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Address.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Address.php
@@ -48,7 +48,7 @@ class Address
      *         If an array of values is passed as the $testValue argument, then the returned result will also be
      *            an array with the same dimensions
      */
-    public static function cell($row, $column, $relativity = 1, $referenceStyle = true, $sheetName = '')
+    public static function cell($row, $column, $relativity = 1, $referenceStyle = true, $sheetName = ''): array|string
     {
         if (
             is_array($row) || is_array($column) ||
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/ExcelMatch.php b/src/PhpSpreadsheet/Calculation/LookupRef/ExcelMatch.php
index e09477c3fa..0ecca4b19b 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/ExcelMatch.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/ExcelMatch.php
@@ -32,7 +32,7 @@ class ExcelMatch
      *
      * @return array|int|string The relative position of the found item
      */
-    public static function MATCH($lookupValue, $lookupArray, $matchType = self::MATCHTYPE_LARGEST_VALUE)
+    public static function MATCH($lookupValue, $lookupArray, $matchType = self::MATCHTYPE_LARGEST_VALUE): array|string|int|float
     {
         if (is_array($lookupValue)) {
             return self::evaluateArrayArgumentsIgnore([self::class, __FUNCTION__], 1, $lookupValue, $lookupArray, $matchType);
@@ -88,10 +88,8 @@ public static function MATCH($lookupValue, $lookupArray, $matchType = self::MATC
 
     /**
      * @param mixed $lookupValue
-     *
-     * @return mixed
      */
-    private static function matchFirstValue(array $lookupArray, $lookupValue)
+    private static function matchFirstValue(array $lookupArray, $lookupValue): int|string|null
     {
         if (is_string($lookupValue)) {
             $valueIsString = true;
@@ -168,10 +166,8 @@ private static function matchLargestValue(array $lookupArray, $lookupValue, arra
 
     /**
      * @param mixed $lookupValue
-     *
-     * @return mixed
      */
-    private static function matchSmallestValue(array $lookupArray, $lookupValue)
+    private static function matchSmallestValue(array $lookupArray, $lookupValue): int|string|null
     {
         $valueKey = null;
         if (is_string($lookupValue)) {
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Indirect.php b/src/PhpSpreadsheet/Calculation/LookupRef/Indirect.php
index bd76ce9306..97a9ff993e 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Indirect.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Indirect.php
@@ -63,7 +63,7 @@ private static function validateAddress($cellAddress): string
      *
      * @return array|string An array containing a cell or range of cells, or a string on error
      */
-    public static function INDIRECT($cellAddress, $a1fmt, Cell $cell)
+    public static function INDIRECT($cellAddress, $a1fmt, Cell $cell): string|array
     {
         [$baseCol, $baseRow] = Coordinate::indexesFromString($cell->getCoordinate());
 
@@ -101,10 +101,10 @@ public static function INDIRECT($cellAddress, $a1fmt, Cell $cell)
     /**
      * Extract range values.
      *
-     * @return mixed Array of values in range if range contains more than one element.
+     * @return array Array of values in range if range contains more than one element.
      *                  Otherwise, a single value is returned.
      */
-    private static function extractRequiredCells(?Worksheet $worksheet, string $cellAddress)
+    private static function extractRequiredCells(?Worksheet $worksheet, string $cellAddress): array
     {
         return Calculation::getInstance($worksheet !== null ? $worksheet->getParent() : null)
             ->extractCellRange($cellAddress, $worksheet, false);
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Matrix.php b/src/PhpSpreadsheet/Calculation/LookupRef/Matrix.php
index 8ee759e87f..402a6bd345 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Matrix.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Matrix.php
@@ -31,10 +31,8 @@ public static function isRowVector(array $values): bool
      * TRANSPOSE.
      *
      * @param array|mixed $matrixData A matrix of values
-     *
-     * @return array
      */
-    public static function transpose($matrixData)
+    public static function transpose($matrixData): array
     {
         $returnMatrix = [];
         if (!is_array($matrixData)) {
@@ -114,7 +112,7 @@ public static function index($matrix, $rowNum = 0, $columnNum = null)
         $columnNum = $columnKeys[--$columnNum];
         if ($rowNum === 0) {
             return array_map(
-                function ($value) {
+                function ($value): array {
                     return [$value];
                 },
                 array_column($matrix, $columnNum)
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Offset.php b/src/PhpSpreadsheet/Calculation/LookupRef/Offset.php
index 562d753978..a8c008ddd5 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Offset.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Offset.php
@@ -39,9 +39,9 @@ class Offset
      * @param mixed $width The width, in number of columns, that you want the returned reference to be.
      *                         Width must be a positive number.
      *
-     * @return array|int|string An array containing a cell or range of cells, or a string on error
+     * @return array|string An array containing a cell or range of cells, or a string on error
      */
-    public static function OFFSET($cellAddress = null, $rows = 0, $columns = 0, $height = null, $width = null, ?Cell $cell = null)
+    public static function OFFSET($cellAddress = null, $rows = 0, $columns = 0, $height = null, $width = null, ?Cell $cell = null): string|array
     {
         $rows = Functions::flattenSingleValue($rows);
         $columns = Functions::flattenSingleValue($columns);
@@ -91,8 +91,7 @@ public static function OFFSET($cellAddress = null, $rows = 0, $columns = 0, $hei
         return self::extractRequiredCells($worksheet, $cellAddress);
     }
 
-    /** @return mixed */
-    private static function extractRequiredCells(?Worksheet $worksheet, string $cellAddress)
+    private static function extractRequiredCells(?Worksheet $worksheet, string $cellAddress): array
     {
         return Calculation::getInstance($worksheet !== null ? $worksheet->getParent() : null)
             ->extractCellRange($cellAddress, $worksheet, false);
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/RowColumnInformation.php b/src/PhpSpreadsheet/Calculation/LookupRef/RowColumnInformation.php
index a1da86c890..91200e0212 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/RowColumnInformation.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/RowColumnInformation.php
@@ -22,7 +22,7 @@ private static function cellAddressNullOrWhitespace($cellAddress): bool
 
     private static function cellColumn(?Cell $cell): int
     {
-        return ($cell !== null) ? (int) Coordinate::columnIndexFromString($cell->getColumn()) : 1;
+        return ($cell !== null) ? Coordinate::columnIndexFromString($cell->getColumn()) : 1;
     }
 
     /**
@@ -42,7 +42,7 @@ private static function cellColumn(?Cell $cell): int
      *
      * @return int|int[]
      */
-    public static function COLUMN($cellAddress = null, ?Cell $cell = null)
+    public static function COLUMN($cellAddress = null, ?Cell $cell = null): int|array
     {
         if (self::cellAddressNullOrWhitespace($cellAddress)) {
             return self::cellColumn($cell);
@@ -52,7 +52,7 @@ public static function COLUMN($cellAddress = null, ?Cell $cell = null)
             foreach ($cellAddress as $columnKey => $value) {
                 $columnKey = (string) preg_replace('/[^a-z]/i', '', $columnKey);
 
-                return (int) Coordinate::columnIndexFromString($columnKey);
+                return Coordinate::columnIndexFromString($columnKey);
             }
 
             return self::cellColumn($cell);
@@ -64,20 +64,22 @@ public static function COLUMN($cellAddress = null, ?Cell $cell = null)
             [,, $cellAddress] = Helpers::extractCellAddresses($cellAddress, true, $cell->getWorksheet(), $sheetName);
         }
         [, $cellAddress] = Worksheet::extractSheetTitle($cellAddress, true);
+        $cellAddress ??= '';
+
         if (strpos($cellAddress, ':') !== false) {
             [$startAddress, $endAddress] = explode(':', $cellAddress);
             $startAddress = (string) preg_replace('/[^a-z]/i', '', $startAddress);
             $endAddress = (string) preg_replace('/[^a-z]/i', '', $endAddress);
 
             return range(
-                (int) Coordinate::columnIndexFromString($startAddress),
-                (int) Coordinate::columnIndexFromString($endAddress)
+                Coordinate::columnIndexFromString($startAddress),
+                Coordinate::columnIndexFromString($endAddress)
             );
         }
 
         $cellAddress = (string) preg_replace('/[^a-z]/i', '', $cellAddress);
 
-        return (int) Coordinate::columnIndexFromString($cellAddress);
+        return Coordinate::columnIndexFromString($cellAddress);
     }
 
     /**
@@ -133,9 +135,9 @@ private static function cellRow(?Cell $cell): int
      *
      * @param null|array|string $cellAddress A reference to a range of cells for which you want the row numbers
      *
-     * @return int|mixed[]|string
+     * @return int|mixed[]
      */
-    public static function ROW($cellAddress = null, ?Cell $cell = null)
+    public static function ROW($cellAddress = null, ?Cell $cell = null): int|array
     {
         if (self::cellAddressNullOrWhitespace($cellAddress)) {
             return self::cellRow($cell);
@@ -157,13 +159,14 @@ public static function ROW($cellAddress = null, ?Cell $cell = null)
             [,, $cellAddress] = Helpers::extractCellAddresses($cellAddress, true, $cell->getWorksheet(), $sheetName);
         }
         [, $cellAddress] = Worksheet::extractSheetTitle($cellAddress, true);
+        $cellAddress ??= '';
         if (strpos($cellAddress, ':') !== false) {
             [$startAddress, $endAddress] = explode(':', $cellAddress);
             $startAddress = (int) (string) preg_replace('/\D/', '', $startAddress);
             $endAddress = (int) (string) preg_replace('/\D/', '', $endAddress);
 
             return array_map(
-                function ($value) {
+                function ($value): array {
                     return [$value];
                 },
                 range($startAddress, $endAddress)
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Sort.php b/src/PhpSpreadsheet/Calculation/LookupRef/Sort.php
index 8f90f18ced..9828da8cb1 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Sort.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Sort.php
@@ -219,7 +219,7 @@ function ($value) {
      * @param array[] $sortIndex
      * @param int[] $sortOrder
      */
-    private static function processSortBy(array $sortArray, array $sortIndex, $sortOrder): array
+    private static function processSortBy(array $sortArray, array $sortIndex, array $sortOrder): array
     {
         $sortArguments = [];
         $sortData = [];
diff --git a/src/PhpSpreadsheet/Calculation/LookupRef/Unique.php b/src/PhpSpreadsheet/Calculation/LookupRef/Unique.php
index 2ba51281ea..4c8b88f250 100644
--- a/src/PhpSpreadsheet/Calculation/LookupRef/Unique.php
+++ b/src/PhpSpreadsheet/Calculation/LookupRef/Unique.php
@@ -104,7 +104,7 @@ private static function countValuesCaseInsensitive(array $caseSensitiveLookupVal
     {
         $caseInsensitiveCounts = array_count_values(
             array_map(
-                function (string $value) {
+                function (string $value): string {
                     return StringHelper::strToUpper($value);
                 },
                 $caseSensitiveLookupValues
@@ -133,7 +133,7 @@ private static function exactlyOnceFilter(array $values): array
     {
         return array_filter(
             $values,
-            function ($value) {
+            function ($value): bool {
                 return $value === 1;
             }
         );
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig.php b/src/PhpSpreadsheet/Calculation/MathTrig.php
index a92e9c82e9..bf40ca43ef 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig.php
@@ -53,7 +53,7 @@ public static function ARABIC($roman)
      *
      * @return array|float|string the inverse tangent of the specified x- and y-coordinates, or a string containing an error
      */
-    public static function ATAN2($xCoordinate = null, $yCoordinate = null)
+    public static function ATAN2($xCoordinate = null, $yCoordinate = null): string|float|array
     {
         return MathTrig\Trig\Tangent::atan2($xCoordinate, $yCoordinate);
     }
@@ -76,7 +76,7 @@ public static function ATAN2($xCoordinate = null, $yCoordinate = null)
      *
      * @return array|string the text representation with the given radix (base)
      */
-    public static function BASE($number, $radix, $minLength = null)
+    public static function BASE($number, $radix, $minLength = null): string|array
     {
         return MathTrig\Base::evaluate($number, $radix, $minLength);
     }
@@ -147,9 +147,9 @@ public static function COMBIN($numObjs, $numInSet)
      *
      * @param array|float $number Number to round
      *
-     * @return array|float|int|string Rounded Number, or a string containing an error
+     * @return array|float|string Rounded Number, or a string containing an error
      */
-    public static function EVEN($number)
+    public static function EVEN($number): string|float|array
     {
         return MathTrig\Round::even($number);
     }
@@ -361,7 +361,7 @@ public static function LCM(...$args)
      *
      * @return array|float|string The result, or a string containing an error
      */
-    public static function logBase($number, $base = 10)
+    public static function logBase($number, $base = 10): string|float|array
     {
         return MathTrig\Logarithms::withBase($number, $base);
     }
@@ -403,7 +403,7 @@ public static function MDETERM($matrixValues)
      *
      * @return array|string The result, or a string containing an error
      */
-    public static function MINVERSE($matrixValues)
+    public static function MINVERSE($matrixValues): string|array
     {
         return MathTrig\MatrixFunctions::inverse($matrixValues);
     }
@@ -420,7 +420,7 @@ public static function MINVERSE($matrixValues)
      *
      * @return array|string The result, or a string containing an error
      */
-    public static function MMULT($matrixData1, $matrixData2)
+    public static function MMULT($matrixData1, $matrixData2): string|array
     {
         return MathTrig\MatrixFunctions::multiply($matrixData1, $matrixData2);
     }
@@ -456,7 +456,7 @@ public static function MOD($a = 1, $b = 1)
      *
      * @return array|float|string Rounded Number, or a string containing an error
      */
-    public static function MROUND($number, $multiple)
+    public static function MROUND($number, $multiple): string|int|float|array
     {
         return MathTrig\Round::multiple($number, $multiple);
     }
@@ -492,7 +492,7 @@ public static function MULTINOMIAL(...$args)
      *
      * @return array|float|int|string Rounded Number, or a string containing an error
      */
-    public static function ODD($number)
+    public static function ODD($number): string|int|float|array
     {
         return MathTrig\Round::odd($number);
     }
@@ -570,9 +570,9 @@ public static function QUOTIENT($numerator, $denominator)
      * @param int $min Minimal value
      * @param int $max Maximal value
      *
-     * @return array|float|int|string Random number
+     * @return array|int|string Random number
      */
-    public static function RAND($min = 0, $max = 0)
+    public static function RAND($min = 0, $max = 0): string|int|array
     {
         return MathTrig\Random::randBetween($min, $max);
     }
@@ -591,7 +591,7 @@ public static function RAND($min = 0, $max = 0)
      *
      * @return array|string Roman numeral, or a string containing an error
      */
-    public static function ROMAN($aValue, $style = 0)
+    public static function ROMAN($aValue, $style = 0): string|array
     {
         return MathTrig\Roman::evaluate($aValue, $style);
     }
@@ -610,7 +610,7 @@ public static function ROMAN($aValue, $style = 0)
      *
      * @return array|float|string Rounded Number, or a string containing an error
      */
-    public static function ROUNDUP($number, $digits)
+    public static function ROUNDUP($number, $digits): string|float|array
     {
         return MathTrig\Round::up($number, $digits);
     }
@@ -629,7 +629,7 @@ public static function ROUNDUP($number, $digits)
      *
      * @return array|float|string Rounded Number, or a string containing an error
      */
-    public static function ROUNDDOWN($number, $digits)
+    public static function ROUNDDOWN($number, $digits): string|float|array
     {
         return MathTrig\Round::down($number, $digits);
     }
@@ -650,7 +650,7 @@ public static function ROUNDDOWN($number, $digits)
      *
      * @return array|float|string The result, or a string containing an error
      */
-    public static function SERIESSUM($x, $n, $m, ...$args)
+    public static function SERIESSUM($x, $n, $m, ...$args): string|float|int|array
     {
         return MathTrig\SeriesSum::evaluate($x, $n, $m, ...$args);
     }
@@ -669,7 +669,7 @@ public static function SERIESSUM($x, $n, $m, ...$args)
      *
      * @return array|int|string sign value, or a string containing an error
      */
-    public static function SIGN($number)
+    public static function SIGN($number): string|int|array
     {
         return MathTrig\Sign::evaluate($number);
     }
@@ -699,7 +699,7 @@ public static function returnSign(float $number): int
      *
      * @return array|float|string Square Root of Number * Pi, or a string containing an error
      */
-    public static function SQRTPI($number)
+    public static function SQRTPI($number): string|float|array
     {
         return MathTrig\Sqrt::pi($number);
     }
@@ -762,13 +762,12 @@ public static function SUM(...$args)
      *      Use the SUMIF() method in the Statistical\Conditional class instead
      * @see Statistical\Conditional::SUMIF()
      *
-     * @param mixed $range Data values
+     * @param array $range Data values
      * @param string $criteria the criteria that defines which cells will be summed
-     * @param mixed $sumRange
      *
      * @return null|float|string
      */
-    public static function SUMIF($range, $criteria, $sumRange = [])
+    public static function SUMIF(array $range, $criteria, array $sumRange = [])
     {
         return Statistical\Conditional::SUMIF($range, $criteria, $sumRange);
     }
@@ -808,7 +807,7 @@ public static function SUMIFS(...$args)
      *
      * @return float|string The result, or a string containing an error
      */
-    public static function SUMPRODUCT(...$args)
+    public static function SUMPRODUCT(...$args): string|int|float
     {
         return MathTrig\Sum::product(...$args);
     }
@@ -1078,7 +1077,7 @@ public static function ACOTH($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinROUND($number, $precision)
+    public static function builtinROUND($number, $precision): string|float|array
     {
         return MathTrig\Round::round($number, $precision);
     }
@@ -1096,7 +1095,7 @@ public static function builtinROUND($number, $precision)
      *
      * @return array|float|int|string Rounded number
      */
-    public static function builtinABS($number)
+    public static function builtinABS($number): string|int|float|array
     {
         return MathTrig\Absolute::evaluate($number);
     }
@@ -1222,7 +1221,7 @@ public static function builtinATANH($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinCOS($number)
+    public static function builtinCOS($number): string|float|array
     {
         return MathTrig\Trig\Cosine::cos($number);
     }
@@ -1240,7 +1239,7 @@ public static function builtinCOS($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinCOSH($number)
+    public static function builtinCOSH($number): string|float|array
     {
         return MathTrig\Trig\Cosine::cosh($number);
     }
@@ -1258,7 +1257,7 @@ public static function builtinCOSH($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinDEGREES($number)
+    public static function builtinDEGREES($number): string|float|array
     {
         return MathTrig\Angle::toDegrees($number);
     }
@@ -1276,7 +1275,7 @@ public static function builtinDEGREES($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinEXP($number)
+    public static function builtinEXP($number): string|float|array
     {
         return MathTrig\Exp::evaluate($number);
     }
@@ -1294,7 +1293,7 @@ public static function builtinEXP($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinLN($number)
+    public static function builtinLN($number): string|float|array
     {
         return MathTrig\Logarithms::natural($number);
     }
@@ -1312,7 +1311,7 @@ public static function builtinLN($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinLOG10($number)
+    public static function builtinLOG10($number): string|float|array
     {
         return MathTrig\Logarithms::base10($number);
     }
@@ -1330,7 +1329,7 @@ public static function builtinLOG10($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinRADIANS($number)
+    public static function builtinRADIANS($number): string|float|array
     {
         return MathTrig\Angle::toRadians($number);
     }
@@ -1348,7 +1347,7 @@ public static function builtinRADIANS($number)
      *
      * @return array|float|string sine
      */
-    public static function builtinSIN($number)
+    public static function builtinSIN($number): string|float|array
     {
         return MathTrig\Trig\Sine::sin($number);
     }
@@ -1366,7 +1365,7 @@ public static function builtinSIN($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinSINH($number)
+    public static function builtinSINH($number): string|float|array
     {
         return MathTrig\Trig\Sine::sinh($number);
     }
@@ -1420,7 +1419,7 @@ public static function builtinTAN($number)
      *
      * @return array|float|string Rounded number
      */
-    public static function builtinTANH($number)
+    public static function builtinTANH($number): string|float|array
     {
         return MathTrig\Trig\Tangent::tanh($number);
     }
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Absolute.php b/src/PhpSpreadsheet/Calculation/MathTrig/Absolute.php
index f21c6b73ca..f45eab9982 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Absolute.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Absolute.php
@@ -20,7 +20,7 @@ class Absolute
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function evaluate($number)
+    public static function evaluate($number): array|string|int|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Angle.php b/src/PhpSpreadsheet/Calculation/MathTrig/Angle.php
index cbeec6f407..2ab984ed29 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Angle.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Angle.php
@@ -20,7 +20,7 @@ class Angle
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toDegrees($number)
+    public static function toDegrees($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
@@ -46,7 +46,7 @@ public static function toDegrees($number)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function toRadians($number)
+    public static function toRadians($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Base.php b/src/PhpSpreadsheet/Calculation/MathTrig/Base.php
index 2fec947326..da11b47bdb 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Base.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Base.php
@@ -29,7 +29,7 @@ class Base
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function evaluate($number, $radix, $minLength = null)
+    public static function evaluate($number, $radix, $minLength = null): array|string
     {
         if (is_array($number) || is_array($radix) || is_array($minLength)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $radix, $minLength);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Ceiling.php b/src/PhpSpreadsheet/Calculation/MathTrig/Ceiling.php
index 635f1bbbb8..f33b63b874 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Ceiling.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Ceiling.php
@@ -70,7 +70,7 @@ public static function ceiling($number, $significance = null)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function math($number, $significance = null, $mode = 0)
+    public static function math($number, $significance = null, $mode = 0): array|string|float
     {
         if (is_array($number) || is_array($significance) || is_array($mode)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $significance, $mode);
@@ -111,7 +111,7 @@ public static function math($number, $significance = null, $mode = 0)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function precise($number, $significance = 1)
+    public static function precise($number, $significance = 1): array|string|float
     {
         if (is_array($number) || is_array($significance)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $significance);
@@ -142,10 +142,8 @@ private static function ceilingMathTest(float $significance, float $number, int
 
     /**
      * Avoid Scrutinizer problems concerning complexity.
-     *
-     * @return float|string
      */
-    private static function argumentsOk(float $number, float $significance)
+    private static function argumentsOk(float $number, float $significance): float|string
     {
         if (empty($number * $significance)) {
             return 0.0;
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Combinations.php b/src/PhpSpreadsheet/Calculation/MathTrig/Combinations.php
index f68c402ae4..d4e70de339 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Combinations.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Combinations.php
@@ -21,11 +21,11 @@ class Combinations
      * @param mixed $numObjs Number of different objects, or can be an array of numbers
      * @param mixed $numInSet Number of objects in each combination, or can be an array of numbers
      *
-     * @return array|float|int|string Number of combinations, or a string containing an error
+     * @return array|float|string Number of combinations, or a string containing an error
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function withoutRepetition($numObjs, $numInSet)
+    public static function withoutRepetition($numObjs, $numInSet): array|string|float
     {
         if (is_array($numObjs) || is_array($numInSet)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $numObjs, $numInSet);
@@ -59,7 +59,7 @@ public static function withoutRepetition($numObjs, $numInSet)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function withRepetition($numObjs, $numInSet)
+    public static function withRepetition($numObjs, $numInSet): array|int|string|float
     {
         if (is_array($numObjs) || is_array($numInSet)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $numObjs, $numInSet);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Exp.php b/src/PhpSpreadsheet/Calculation/MathTrig/Exp.php
index f65c2c18bf..288cd84690 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Exp.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Exp.php
@@ -20,7 +20,7 @@ class Exp
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function evaluate($number)
+    public static function evaluate($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Factorial.php b/src/PhpSpreadsheet/Calculation/MathTrig/Factorial.php
index 8059eec8b7..02143b07c0 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Factorial.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Factorial.php
@@ -27,7 +27,7 @@ class Factorial
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function fact($factVal)
+    public static function fact($factVal): array|string|float|int
     {
         if (is_array($factVal)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $factVal);
@@ -69,7 +69,7 @@ public static function fact($factVal)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function factDouble($factVal)
+    public static function factDouble($factVal): array|string|float|int
     {
         if (is_array($factVal)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $factVal);
@@ -101,7 +101,7 @@ public static function factDouble($factVal)
      *
      * @return float|string The result, or a string containing an error
      */
-    public static function multinomial(...$args)
+    public static function multinomial(...$args): string|int|float
     {
         $summer = 0;
         $divisor = 1;
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Floor.php b/src/PhpSpreadsheet/Calculation/MathTrig/Floor.php
index 2199dda0c1..8f75cea0b1 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Floor.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Floor.php
@@ -127,10 +127,8 @@ public static function precise($number, $significance = 1)
 
     /**
      * Avoid Scrutinizer problems concerning complexity.
-     *
-     * @return float|string
      */
-    private static function argumentsOkPrecise(float $number, float $significance)
+    private static function argumentsOkPrecise(float $number, float $significance): string|float
     {
         if ($significance == 0.0) {
             return ExcelError::DIV0();
@@ -147,7 +145,7 @@ private static function argumentsOkPrecise(float $number, float $significance)
      *
      * @return float|string Rounded Number, or a string containing an error
      */
-    private static function argsOk(float $number, float $significance, int $mode)
+    private static function argsOk(float $number, float $significance, int $mode): string|float
     {
         if (!$significance) {
             return ExcelError::DIV0();
@@ -172,10 +170,8 @@ private static function floorMathTest(float $number, float $significance, int $m
 
     /**
      * Avoid Scrutinizer problems concerning complexity.
-     *
-     * @return float|string
      */
-    private static function argumentsOk(float $number, float $significance)
+    private static function argumentsOk(float $number, float $significance): string|float
     {
         if ($significance == 0.0) {
             return ExcelError::DIV0();
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Helpers.php b/src/PhpSpreadsheet/Calculation/MathTrig/Helpers.php
index f34f159b8f..0b85435064 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Helpers.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Helpers.php
@@ -13,7 +13,7 @@ class Helpers
      *
      * @return float|string quotient or DIV0 if denominator is too small
      */
-    public static function verySmallDenominator(float $numerator, float $denominator)
+    public static function verySmallDenominator(float $numerator, float $denominator): string|float
     {
         return (abs($denominator) < 1.0E-12) ? ExcelError::DIV0() : ($numerator / $denominator);
     }
@@ -22,10 +22,8 @@ public static function verySmallDenominator(float $numerator, float $denominator
      * Many functions accept null/false/true argument treated as 0/0/1.
      *
      * @param mixed $number
-     *
-     * @return float|int
      */
-    public static function validateNumericNullBool($number)
+    public static function validateNumericNullBool($number): int|float
     {
         $number = Functions::flattenSingleValue($number);
         if ($number === null) {
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/IntClass.php b/src/PhpSpreadsheet/Calculation/MathTrig/IntClass.php
index 230f969a29..76bbced8d5 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/IntClass.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/IntClass.php
@@ -23,7 +23,7 @@ class IntClass
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function evaluate($number)
+    public static function evaluate($number): array|string|int
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Lcm.php b/src/PhpSpreadsheet/Calculation/MathTrig/Lcm.php
index 3b23c1da17..652f31c937 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Lcm.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Lcm.php
@@ -49,7 +49,7 @@ private static function factors(float $value): array
      *
      * @return int|string Lowest Common Multiplier, or a string containing an error
      */
-    public static function evaluate(...$args)
+    public static function evaluate(...$args): int|string
     {
         try {
             $arrayArgs = [];
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Logarithms.php b/src/PhpSpreadsheet/Calculation/MathTrig/Logarithms.php
index 7b07f09d51..464781e6f2 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Logarithms.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Logarithms.php
@@ -26,7 +26,7 @@ class Logarithms
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function withBase($number, $base = 10)
+    public static function withBase($number, $base = 10): array|string|float
     {
         if (is_array($number) || is_array($base)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $base);
@@ -56,7 +56,7 @@ public static function withBase($number, $base = 10)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function base10($number)
+    public static function base10($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
@@ -84,7 +84,7 @@ public static function base10($number)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function natural($number)
+    public static function natural($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/MatrixFunctions.php b/src/PhpSpreadsheet/Calculation/MathTrig/MatrixFunctions.php
index 5a5125a8c0..e1bd837f56 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/MatrixFunctions.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/MatrixFunctions.php
@@ -57,7 +57,7 @@ private static function getMatrix($matrixValues): Matrix
      *
      * @return array|string The resulting array, or a string containing an error
      */
-    public static function sequence($rows = 1, $columns = 1, $start = 1, $step = 1)
+    public static function sequence($rows = 1, $columns = 1, $start = 1, $step = 1): string|array
     {
         try {
             $rows = (int) Helpers::validateNumericNullSubstitution($rows, 1);
@@ -120,7 +120,7 @@ public static function determinant($matrixValues)
      *
      * @return array|string The result, or a string containing an error
      */
-    public static function inverse($matrixValues)
+    public static function inverse($matrixValues): array|string
     {
         try {
             $matrix = self::getMatrix($matrixValues);
@@ -143,7 +143,7 @@ public static function inverse($matrixValues)
      *
      * @return array|string The result, or a string containing an error
      */
-    public static function multiply($matrixData1, $matrixData2)
+    public static function multiply($matrixData1, $matrixData2): array|string
     {
         try {
             $matrixA = self::getMatrix($matrixData1);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Operations.php b/src/PhpSpreadsheet/Calculation/MathTrig/Operations.php
index 0625845105..f8857ec4b2 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Operations.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Operations.php
@@ -19,11 +19,11 @@ class Operations
      * @param mixed $divisor Divisor
      *                      Or can be an array of values
      *
-     * @return array|float|int|string Remainder, or a string containing an error
+     * @return array|float|string Remainder, or a string containing an error
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function mod($dividend, $divisor)
+    public static function mod($dividend, $divisor): array|string|float
     {
         if (is_array($dividend) || is_array($divisor)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $dividend, $divisor);
@@ -97,14 +97,12 @@ public static function power($x, $y)
      *        PRODUCT(value1[,value2[, ...]])
      *
      * @param mixed ...$args Data values
-     *
-     * @return float|string
      */
-    public static function product(...$args)
+    public static function product(...$args): string|float
     {
         $args = array_filter(
             Functions::flattenArray($args),
-            function ($value) {
+            function ($value): bool {
                 return $value !== null;
             }
         );
@@ -143,7 +141,7 @@ function ($value) {
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function quotient($numerator, $denominator)
+    public static function quotient($numerator, $denominator): array|string|int
     {
         if (is_array($numerator) || is_array($denominator)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $numerator, $denominator);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Random.php b/src/PhpSpreadsheet/Calculation/MathTrig/Random.php
index 22cad2cfd9..2c60e2b463 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Random.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Random.php
@@ -15,7 +15,7 @@ class Random
      *
      * @return float Random number
      */
-    public static function rand()
+    public static function rand(): int|float
     {
         return mt_rand(0, 10000000) / 10000000;
     }
@@ -28,11 +28,11 @@ public static function rand()
      * @param mixed $max Maximal value
      *                      Or can be an array of values
      *
-     * @return array|float|int|string Random number
+     * @return array|int|string Random number
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function randBetween($min, $max)
+    public static function randBetween($min, $max): array|string|int
     {
         if (is_array($min) || is_array($max)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $min, $max);
@@ -67,7 +67,7 @@ public static function randBetween($min, $max)
      *
      * @return array|string The resulting array, or a string containing an error
      */
-    public static function randArray($rows = 1, $columns = 1, $min = 0, $max = 1, $wholeNumber = false)
+    public static function randArray($rows = 1, $columns = 1, $min = 0, $max = 1, $wholeNumber = false): string|array
     {
         try {
             $rows = (int) Helpers::validateNumericNullSubstitution($rows, 1);
@@ -86,7 +86,7 @@ public static function randArray($rows = 1, $columns = 1, $min = 0, $max = 1, $w
 
         return array_chunk(
             array_map(
-                function () use ($min, $max, $wholeNumber) {
+                function () use ($min, $max, $wholeNumber): int|float {
                     return $wholeNumber
                         ? mt_rand((int) $min, (int) $max)
                         : (mt_rand() / mt_getrandmax()) * ($max - $min) + $min;
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Roman.php b/src/PhpSpreadsheet/Calculation/MathTrig/Roman.php
index 05415481c3..cd21202a71 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Roman.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Roman.php
@@ -825,7 +825,7 @@ public static function calculateRoman(int $aValue, int $style): string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function evaluate($aValue, $style = 0)
+    public static function evaluate($aValue, $style = 0): array|string
     {
         if (is_array($aValue) || is_array($style)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $aValue, $style);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Round.php b/src/PhpSpreadsheet/Calculation/MathTrig/Round.php
index 776f7eb902..882e6283f9 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Round.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Round.php
@@ -22,7 +22,7 @@ class Round
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function round($number, $precision)
+    public static function round($number, $precision): array|string|float
     {
         if (is_array($number) || is_array($precision)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $precision);
@@ -50,7 +50,7 @@ public static function round($number, $precision)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function up($number, $digits)
+    public static function up($number, $digits): array|string|float
     {
         if (is_array($number) || is_array($digits)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $digits);
@@ -86,7 +86,7 @@ public static function up($number, $digits)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function down($number, $digits)
+    public static function down($number, $digits): array|string|float
     {
         if (is_array($number) || is_array($digits)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $digits);
@@ -122,7 +122,7 @@ public static function down($number, $digits)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function multiple($number, $multiple)
+    public static function multiple($number, $multiple): array|string|int|float
     {
         if (is_array($number) || is_array($multiple)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $number, $multiple);
@@ -165,7 +165,7 @@ public static function multiple($number, $multiple)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function even($number)
+    public static function even($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
@@ -191,7 +191,7 @@ public static function even($number)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function odd($number)
+    public static function odd($number): array|string|int|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/SeriesSum.php b/src/PhpSpreadsheet/Calculation/MathTrig/SeriesSum.php
index ecce359fc6..b2745b0ce9 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/SeriesSum.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/SeriesSum.php
@@ -22,7 +22,7 @@ class SeriesSum
      *
      * @return array|float|string The result, or a string containing an error
      */
-    public static function evaluate($x, $n, $m, ...$args)
+    public static function evaluate($x, $n, $m, ...$args): array|string|float|int
     {
         if (is_array($x) || is_array($n) || is_array($m)) {
             return self::evaluateArrayArgumentsSubset([self::class, __FUNCTION__], 3, $x, $n, $m, ...$args);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Sign.php b/src/PhpSpreadsheet/Calculation/MathTrig/Sign.php
index e40e1f6d36..86a55092c7 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Sign.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Sign.php
@@ -21,7 +21,7 @@ class Sign
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function evaluate($number)
+    public static function evaluate($number): array|string|int
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Sqrt.php b/src/PhpSpreadsheet/Calculation/MathTrig/Sqrt.php
index bb9f15fda5..37bef7bfae 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Sqrt.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Sqrt.php
@@ -46,7 +46,7 @@ public static function sqrt($number)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function pi($number)
+    public static function pi($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Subtotal.php b/src/PhpSpreadsheet/Calculation/MathTrig/Subtotal.php
index 6d8f4723c1..9d343676b8 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Subtotal.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Subtotal.php
@@ -38,7 +38,7 @@ protected static function filterFormulaArgs($cellReference, $args): array
     {
         return array_filter(
             $args,
-            function ($index) use ($cellReference) {
+            function ($index) use ($cellReference): bool {
                 $explodeArray = explode('.', $index);
                 $row = $explodeArray[1] ?? '';
                 $column = $explodeArray[2] ?? '';
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Sum.php b/src/PhpSpreadsheet/Calculation/MathTrig/Sum.php
index 37070e2434..d6bf2d9d29 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Sum.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Sum.php
@@ -79,9 +79,9 @@ public static function sumErroringStrings(...$args)
      *
      * @param mixed ...$args Data values
      *
-     * @return float|string The result, or a string containing an error
+     * @return float|int|string The result, or a string containing an error
      */
-    public static function product(...$args)
+    public static function product(...$args): string|int|float
     {
         $arrayList = $args;
 
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/SumSquares.php b/src/PhpSpreadsheet/Calculation/MathTrig/SumSquares.php
index 34b397cde2..30e7c5e87c 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/SumSquares.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/SumSquares.php
@@ -20,7 +20,7 @@ class SumSquares
      *
      * @return float|string
      */
-    public static function sumSquare(...$args)
+    public static function sumSquare(...$args): string|int|float
     {
         try {
             $returnValue = 0;
@@ -65,7 +65,7 @@ private static function numericNotString($item): bool
      *
      * @return float|string
      */
-    public static function sumXSquaredMinusYSquared($matrixData1, $matrixData2)
+    public static function sumXSquaredMinusYSquared($matrixData1, $matrixData2): string|int|float
     {
         try {
             $array1 = Functions::flattenArray($matrixData1);
@@ -93,7 +93,7 @@ public static function sumXSquaredMinusYSquared($matrixData1, $matrixData2)
      *
      * @return float|string
      */
-    public static function sumXSquaredPlusYSquared($matrixData1, $matrixData2)
+    public static function sumXSquaredPlusYSquared($matrixData1, $matrixData2): string|int|float
     {
         try {
             $array1 = Functions::flattenArray($matrixData1);
@@ -121,7 +121,7 @@ public static function sumXSquaredPlusYSquared($matrixData1, $matrixData2)
      *
      * @return float|string
      */
-    public static function sumXMinusYSquared($matrixData1, $matrixData2)
+    public static function sumXMinusYSquared($matrixData1, $matrixData2): string|int|float
     {
         try {
             $array1 = Functions::flattenArray($matrixData1);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cosine.php b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cosine.php
index c06f04dfc1..28e1220b3c 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cosine.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cosine.php
@@ -21,7 +21,7 @@ class Cosine
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function cos($number)
+    public static function cos($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
@@ -47,7 +47,7 @@ public static function cos($number)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function cosh($number)
+    public static function cosh($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cotangent.php b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cotangent.php
index eeedef9bfc..861159a3bd 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cotangent.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Cotangent.php
@@ -73,7 +73,7 @@ public static function coth($angle)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function acot($number)
+    public static function acot($number): array|string|float
     {
         if (is_array($number)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $number);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Sine.php b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Sine.php
index 6af568ce23..050e36e92e 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Sine.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Sine.php
@@ -21,7 +21,7 @@ class Sine
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function sin($angle)
+    public static function sin($angle): array|string|float
     {
         if (is_array($angle)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $angle);
@@ -47,7 +47,7 @@ public static function sin($angle)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function sinh($angle)
+    public static function sinh($angle): array|string|float
     {
         if (is_array($angle)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $angle);
diff --git a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Tangent.php b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Tangent.php
index 9e77021028..8667e582ac 100644
--- a/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Tangent.php
+++ b/src/PhpSpreadsheet/Calculation/MathTrig/Trig/Tangent.php
@@ -48,7 +48,7 @@ public static function tan($angle)
      *         If an array of numbers is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function tanh($angle)
+    public static function tanh($angle): array|string|float
     {
         if (is_array($angle)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $angle);
@@ -139,7 +139,7 @@ public static function atanh($number)
      *         If an array of numbers is passed as one of the arguments, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function atan2($xCoordinate, $yCoordinate)
+    public static function atan2($xCoordinate, $yCoordinate): array|string|float
     {
         if (is_array($xCoordinate) || is_array($yCoordinate)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $xCoordinate, $yCoordinate);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical.php b/src/PhpSpreadsheet/Calculation/Statistical.php
index 6310ef37cf..1c81631ad6 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical.php
@@ -124,10 +124,8 @@ public static function AVERAGEIF($range, $condition, $averageRange = [])
      * @param float $beta Parameter to the distribution
      * @param mixed $rMin
      * @param mixed $rMax
-     *
-     * @return array|float|string
      */
-    public static function BETADIST($value, $alpha, $beta, $rMin = 0, $rMax = 1)
+    public static function BETADIST($value, $alpha, $beta, $rMin = 0, $rMax = 1): string|float|array
     {
         return Statistical\Distributions\Beta::distribution($value, $alpha, $beta, $rMin, $rMax);
     }
@@ -269,10 +267,8 @@ public static function CORREL($yValues, $xValues = null)
      * @see Statistical\Counts::COUNT()
      *
      * @param mixed ...$args Data values
-     *
-     * @return int
      */
-    public static function COUNT(...$args)
+    public static function COUNT(...$args): int
     {
         return Counts::COUNT(...$args);
     }
@@ -290,10 +286,8 @@ public static function COUNT(...$args)
      * @see Statistical\Counts::COUNTA()
      *
      * @param mixed ...$args Data values
-     *
-     * @return int
      */
-    public static function COUNTA(...$args)
+    public static function COUNTA(...$args): int
     {
         return Counts::COUNTA(...$args);
     }
@@ -311,10 +305,8 @@ public static function COUNTA(...$args)
      * @see Statistical\Counts::COUNTBLANK()
      *
      * @param mixed $range Data values
-     *
-     * @return int
      */
-    public static function COUNTBLANK($range)
+    public static function COUNTBLANK($range): int
     {
         return Counts::COUNTBLANK($range);
     }
@@ -371,12 +363,12 @@ public static function COUNTIFS(...$args)
      *      Use the COVAR() method in the Statistical\Trends class instead
      * @see Statistical\Trends::COVAR()
      *
-     * @param mixed $yValues array of mixed Data Series Y
-     * @param mixed $xValues array of mixed Data Series X
+     * @param mixed[] $yValues array of mixed Data Series Y
+     * @param mixed[] $xValues array of mixed Data Series X
      *
      * @return float|string
      */
-    public static function COVAR($yValues, $xValues)
+    public static function COVAR(array $yValues, array $xValues)
     {
         return Trends::COVAR($yValues, $xValues);
     }
@@ -522,12 +514,12 @@ public static function FISHERINV($value)
      * @see Statistical\Trends::FORECAST()
      *
      * @param float $xValue Value of X for which we want to find Y
-     * @param mixed $yValues array of mixed Data Series Y
-     * @param mixed $xValues of mixed Data Series X
+     * @param mixed[] $yValues array of mixed Data Series Y
+     * @param mixed[] $xValues array of mixed Data Series X
      *
      * @return array|bool|float|string
      */
-    public static function FORECAST($xValue, $yValues, $xValues)
+    public static function FORECAST($xValue, array $yValues, array $xValues)
     {
         return Trends::FORECAST($xValue, $yValues, $xValues);
     }
@@ -545,7 +537,7 @@ public static function FORECAST($xValue, $yValues, $xValues)
      *
      * @return array|float|string The result, or a string containing an error
      */
-    public static function GAMMAFunction($value)
+    public static function GAMMAFunction($value): string|float|array
     {
         return Statistical\Distributions\Gamma::gamma($value);
     }
@@ -601,10 +593,8 @@ public static function GAMMAINV($probability, $alpha, $beta)
      * @see Statistical\Distributions\Gamma::ln()
      *
      * @param float $value
-     *
-     * @return array|float|string
      */
-    public static function GAMMALN($value)
+    public static function GAMMALN($value): string|float|array
     {
         return Statistical\Distributions\Gamma::ln($value);
     }
@@ -735,7 +725,7 @@ public static function HYPGEOMDIST($sampleSuccesses, $sampleNumber, $populationS
      *
      * @return float|string
      */
-    public static function INTERCEPT($yValues, $xValues)
+    public static function INTERCEPT(array $yValues, array $xValues)
     {
         return Trends::INTERCEPT($yValues, $xValues);
     }
@@ -798,9 +788,9 @@ public static function LARGE(...$args)
      * @param bool $const a logical value specifying whether to force the intersect to equal 0
      * @param bool $stats a logical value specifying whether to return additional regression statistics
      *
-     * @return array|int|string The result, or a string containing an error
+     * @return array|string The result, or a string containing an error
      */
-    public static function LINEST($yValues, $xValues = null, $const = true, $stats = false)
+    public static function LINEST(array $yValues, $xValues = null, $const = true, $stats = false): string|array
     {
         return Trends::LINEST($yValues, $xValues, $const, $stats);
     }
@@ -820,9 +810,9 @@ public static function LINEST($yValues, $xValues = null, $const = true, $stats =
      * @param bool $const a logical value specifying whether to force the intersect to equal 0
      * @param bool $stats a logical value specifying whether to return additional regression statistics
      *
-     * @return array|int|string The result, or a string containing an error
+     * @return array|string The result, or a string containing an error
      */
-    public static function LOGEST($yValues, $xValues = null, $const = true, $stats = false)
+    public static function LOGEST(array $yValues, $xValues = null, $const = true, $stats = false): string|array
     {
         return Trends::LOGEST($yValues, $xValues, $const, $stats);
     }
@@ -846,7 +836,7 @@ public static function LOGEST($yValues, $xValues = null, $const = true, $stats =
      *            accuracy if I can get my head round the mathematics
      *            (as described at) http://home.online.no/~pjacklam/notes/invnorm/
      */
-    public static function LOGINV($probability, $mean, $stdDev)
+    public static function LOGINV($probability, $mean, $stdDev): string|float|array
     {
         return Statistical\Distributions\LogNormal::inverse($probability, $mean, $stdDev);
     }
@@ -1229,7 +1219,7 @@ public static function PERCENTILE(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function PERCENTRANK($valueSet, $value, $significance = 3)
+    public static function PERCENTRANK($valueSet, $value, $significance = 3): string|float
     {
         return Statistical\Percentiles::PERCENTRANK($valueSet, $value, $significance);
     }
@@ -1334,7 +1324,7 @@ public static function RANK($value, $valueSet, $order = 0)
      *
      * @return float|string The result, or a string containing an error
      */
-    public static function RSQ($yValues, $xValues)
+    public static function RSQ(array $yValues, array $xValues)
     {
         return Trends::RSQ($yValues, $xValues);
     }
@@ -1374,7 +1364,7 @@ public static function SKEW(...$args)
      *
      * @return float|string The result, or a string containing an error
      */
-    public static function SLOPE($yValues, $xValues)
+    public static function SLOPE(array $yValues, array $xValues)
     {
         return Trends::SLOPE($yValues, $xValues);
     }
@@ -1520,7 +1510,7 @@ public static function STDEVPA(...$args)
      *
      * @return float|string
      */
-    public static function STEYX($yValues, $xValues)
+    public static function STEYX(array $yValues, array $xValues)
     {
         return Trends::STEYX($yValues, $xValues);
     }
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/AggregateBase.php b/src/PhpSpreadsheet/Calculation/Statistical/AggregateBase.php
index 10933f488e..0002a5e4c1 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/AggregateBase.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/AggregateBase.php
@@ -44,10 +44,8 @@ protected static function testAcceptedBoolean($arg, $k)
     /**
      * @param mixed $arg
      * @param mixed $k
-     *
-     * @return bool
      */
-    protected static function isAcceptedCountable($arg, $k, bool $countNull = false)
+    protected static function isAcceptedCountable($arg, $k, bool $countNull = false): bool
     {
         if ($countNull && $arg === null && !Functions::isCellValue($k) && Functions::getCompatibilityMode() !== Functions::COMPATIBILITY_GNUMERIC) {
             return true;
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Averages.php b/src/PhpSpreadsheet/Calculation/Statistical/Averages.php
index edb29847c6..304fe877f5 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Averages.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Averages.php
@@ -20,7 +20,7 @@ class Averages extends AggregateBase
      *
      * @return float|string (string if result is an error)
      */
-    public static function averageDeviations(...$args)
+    public static function averageDeviations(...$args): string|float
     {
         $aArgs = Functions::flattenArrayIndexed($args);
 
@@ -69,7 +69,7 @@ public static function averageDeviations(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function average(...$args)
+    public static function average(...$args): string|int|float
     {
         $returnValue = $aCount = 0;
 
@@ -108,7 +108,7 @@ public static function average(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function averageA(...$args)
+    public static function averageA(...$args): string|int|float
     {
         $returnValue = null;
 
@@ -200,7 +200,7 @@ protected static function filterArguments(array $args): array
     {
         return array_filter(
             $args,
-            function ($value) {
+            function ($value): bool {
                 // Is it a numeric value?
                 return  is_numeric($value) && (!is_string($value));
             }
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Averages/Mean.php b/src/PhpSpreadsheet/Calculation/Statistical/Averages/Mean.php
index 001c91eb32..23697d4738 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Averages/Mean.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Averages/Mean.php
@@ -25,7 +25,7 @@ class Mean
      *
      * @return float|string
      */
-    public static function geometric(...$args)
+    public static function geometric(...$args): float|int|string
     {
         $aArgs = Functions::flattenArray($args);
 
@@ -53,7 +53,7 @@ public static function geometric(...$args)
      *
      * @return float|string
      */
-    public static function harmonic(...$args)
+    public static function harmonic(...$args): string|float|int
     {
         // Loop through arguments
         $aArgs = Functions::flattenArray($args);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Conditional.php b/src/PhpSpreadsheet/Calculation/Statistical/Conditional.php
index 105db96317..9f4b7d631c 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Conditional.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Conditional.php
@@ -82,15 +82,13 @@ public static function AVERAGEIFS(...$args)
      *
      * @param mixed[] $range Data values
      * @param string $condition the criteria that defines which cells will be counted
-     *
-     * @return int|string
      */
-    public static function COUNTIF($range, $condition)
+    public static function COUNTIF($range, $condition): string|int
     {
         // Filter out any empty values that shouldn't be included in a COUNT
         $range = array_filter(
             Functions::flattenArray($range),
-            function ($value) {
+            function ($value): bool {
                 return $value !== null && $value !== '';
             }
         );
@@ -183,13 +181,12 @@ public static function MINIFS(...$args)
      * Excel Function:
      *        SUMIF(range, criteria, [sum_range])
      *
-     * @param mixed $range Data values
-     * @param mixed $sumRange
+     * @param array $range Data values
      * @param mixed $condition
      *
      * @return null|float|string
      */
-    public static function SUMIF($range, $condition, $sumRange = [])
+    public static function SUMIF(array $range, $condition, array $sumRange = [])
     {
         $database = self::databaseFromRangeAndValue($range, $sumRange);
         $condition = [[self::CONDITION_COLUMN_NAME, self::VALUE_COLUMN_NAME], [$condition, null]];
@@ -239,7 +236,7 @@ private static function buildConditionSetForValueRange(...$args): array
 
         if (count($conditions) === 1) {
             return array_map(
-                function ($value) {
+                function ($value): array {
                     return [$value];
                 },
                 $conditions[0]
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Counts.php b/src/PhpSpreadsheet/Calculation/Statistical/Counts.php
index 6792730387..80b15c43c4 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Counts.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Counts.php
@@ -16,10 +16,8 @@ class Counts extends AggregateBase
      *        COUNT(value1[,value2[, ...]])
      *
      * @param mixed ...$args Data values
-     *
-     * @return int
      */
-    public static function COUNT(...$args)
+    public static function COUNT(...$args): int
     {
         $returnValue = 0;
 
@@ -47,10 +45,8 @@ public static function COUNT(...$args)
      *        COUNTA(value1[,value2[, ...]])
      *
      * @param mixed ...$args Data values
-     *
-     * @return int
      */
-    public static function COUNTA(...$args)
+    public static function COUNTA(...$args): int
     {
         $returnValue = 0;
 
@@ -75,10 +71,8 @@ public static function COUNTA(...$args)
      *        COUNTBLANK(value1[,value2[, ...]])
      *
      * @param mixed $range Data values
-     *
-     * @return int
      */
-    public static function COUNTBLANK($range)
+    public static function COUNTBLANK($range): int
     {
         if ($range === null) {
             return 1;
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Deviations.php b/src/PhpSpreadsheet/Calculation/Statistical/Deviations.php
index 280ecfe0dc..1efb69c86a 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Deviations.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Deviations.php
@@ -16,10 +16,8 @@ class Deviations
      *        DEVSQ(value1[,value2[, ...]])
      *
      * @param mixed ...$args Data values
-     *
-     * @return float|string
      */
-    public static function sumSquares(...$args)
+    public static function sumSquares(...$args): string|float
     {
         $aArgs = Functions::flattenArrayIndexed($args);
 
@@ -61,7 +59,7 @@ public static function sumSquares(...$args)
      *
      * @return float|string
      */
-    public static function kurtosis(...$args)
+    public static function kurtosis(...$args): string|int|float
     {
         $aArgs = Functions::flattenArrayIndexed($args);
         $mean = Averages::average($aArgs);
@@ -106,7 +104,7 @@ public static function kurtosis(...$args)
      *
      * @return float|int|string The result, or a string containing an error
      */
-    public static function skew(...$args)
+    public static function skew(...$args): string|int|float
     {
         $aArgs = Functions::flattenArrayIndexed($args);
         $mean = Averages::average($aArgs);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Beta.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Beta.php
index a88c1054a6..e2faa6f207 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Beta.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Beta.php
@@ -37,7 +37,7 @@ class Beta
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value, $alpha, $beta, $rMin = 0.0, $rMax = 1.0)
+    public static function distribution($value, $alpha, $beta, $rMin = 0.0, $rMax = 1.0): array|string|float
     {
         if (is_array($value) || is_array($alpha) || is_array($beta) || is_array($rMin) || is_array($rMax)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $alpha, $beta, $rMin, $rMax);
@@ -91,7 +91,7 @@ public static function distribution($value, $alpha, $beta, $rMin = 0.0, $rMax =
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function inverse($probability, $alpha, $beta, $rMin = 0.0, $rMax = 1.0)
+    public static function inverse($probability, $alpha, $beta, $rMin = 0.0, $rMax = 1.0): array|string|float
     {
         if (is_array($probability) || is_array($alpha) || is_array($beta) || is_array($rMin) || is_array($rMax)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $probability, $alpha, $beta, $rMin, $rMax);
@@ -122,10 +122,7 @@ public static function inverse($probability, $alpha, $beta, $rMin = 0.0, $rMax =
         return self::calculateInverse($probability, $alpha, $beta, $rMin, $rMax);
     }
 
-    /**
-     * @return float|string
-     */
-    private static function calculateInverse(float $probability, float $alpha, float $beta, float $rMin, float $rMax)
+    private static function calculateInverse(float $probability, float $alpha, float $beta, float $rMin, float $rMax): string|float
     {
         $a = 0;
         $b = 2;
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Binomial.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Binomial.php
index 02b53e888e..33d0d8ef12 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Binomial.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Binomial.php
@@ -83,7 +83,7 @@ public static function distribution($value, $trials, $probability, $cumulative)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function range($trials, $probability, $successes, $limit = null)
+    public static function range($trials, $probability, $successes, $limit = null): array|string|float|int
     {
         if (is_array($trials) || is_array($probability) || is_array($successes) || is_array($limit)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $trials, $probability, $successes, $limit);
@@ -141,7 +141,7 @@ public static function range($trials, $probability, $successes, $limit = null)
      * TODO Add support for the cumulative flag not present for NEGBINOMDIST, but introduced for NEGBINOM.DIST
      *      The cumulative default should be false to reflect the behaviour of NEGBINOMDIST
      */
-    public static function negative($failures, $successes, $probability)
+    public static function negative($failures, $successes, $probability): array|string|float
     {
         if (is_array($failures) || is_array($successes) || is_array($probability)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $failures, $successes, $probability);
@@ -187,7 +187,7 @@ public static function negative($failures, $successes, $probability)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function inverse($trials, $probability, $alpha)
+    public static function inverse($trials, $probability, $alpha): array|string|int
     {
         if (is_array($trials) || is_array($probability) || is_array($alpha)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $trials, $probability, $alpha);
@@ -219,10 +219,7 @@ public static function inverse($trials, $probability, $alpha)
         return $successes;
     }
 
-    /**
-     * @return float|int
-     */
-    private static function calculateCumulativeBinomial(int $value, int $trials, float $probability)
+    private static function calculateCumulativeBinomial(int $value, int $trials, float $probability): float|int
     {
         $summer = 0;
         for ($i = 0; $i <= $value; ++$i) {
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/ChiSquared.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/ChiSquared.php
index 3538412850..56dea71fcf 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/ChiSquared.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/ChiSquared.php
@@ -27,7 +27,7 @@ class ChiSquared
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distributionRightTail($value, $degrees)
+    public static function distributionRightTail($value, $degrees): array|string|int|float
     {
         if (is_array($value) || is_array($degrees)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $degrees);
@@ -70,7 +70,7 @@ public static function distributionRightTail($value, $degrees)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distributionLeftTail($value, $degrees, $cumulative)
+    public static function distributionLeftTail($value, $degrees, $cumulative): array|string|int|float
     {
         if (is_array($value) || is_array($degrees) || is_array($cumulative)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $degrees, $cumulative);
@@ -136,7 +136,7 @@ public static function inverseRightTail($probability, $degrees)
             return ExcelError::NAN();
         }
 
-        $callback = function ($value) use ($degrees) {
+        $callback = function ($value) use ($degrees): float {
             return 1 - (Gamma::incompleteGamma($degrees / 2, $value / 2)
                     / Gamma::gammaValue($degrees / 2));
         };
@@ -160,7 +160,7 @@ public static function inverseRightTail($probability, $degrees)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function inverseLeftTail($probability, $degrees)
+    public static function inverseLeftTail($probability, $degrees): array|string|float
     {
         if (is_array($probability) || is_array($degrees)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $probability, $degrees);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Exponential.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Exponential.php
index a03671cccd..e8627c9f6d 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Exponential.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Exponential.php
@@ -28,7 +28,7 @@ class Exponential
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value, $lambda, $cumulative)
+    public static function distribution($value, $lambda, $cumulative): array|string|float
     {
         if (is_array($value) || is_array($lambda) || is_array($cumulative)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $lambda, $cumulative);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/F.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/F.php
index ff413b6b82..7186239b22 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/F.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/F.php
@@ -31,7 +31,7 @@ class F
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value, $u, $v, $cumulative)
+    public static function distribution($value, $u, $v, $cumulative): array|string|float
     {
         if (is_array($value) || is_array($u) || is_array($v) || is_array($cumulative)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $u, $v, $cumulative);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Fisher.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Fisher.php
index df9906ea9f..d7bdc6ff1b 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Fisher.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Fisher.php
@@ -24,7 +24,7 @@ class Fisher
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value)
+    public static function distribution($value): array|string|float
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -57,7 +57,7 @@ public static function distribution($value)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function inverse($probability)
+    public static function inverse($probability): array|string|float
     {
         if (is_array($probability)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $probability);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Gamma.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Gamma.php
index 216f234c1e..e278007982 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Gamma.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Gamma.php
@@ -22,7 +22,7 @@ class Gamma extends GammaBase
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function gamma($value)
+    public static function gamma($value): array|string|float
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -130,7 +130,7 @@ public static function inverse($probability, $alpha, $beta)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function ln($value)
+    public static function ln($value): array|string|float
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/HyperGeometric.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/HyperGeometric.php
index b3ad69d1af..d8012b87e7 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/HyperGeometric.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/HyperGeometric.php
@@ -30,7 +30,7 @@ class HyperGeometric
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($sampleSuccesses, $sampleNumber, $populationSuccesses, $populationNumber)
+    public static function distribution($sampleSuccesses, $sampleNumber, $populationSuccesses, $populationNumber): array|string|float
     {
         if (
             is_array($sampleSuccesses) || is_array($sampleNumber) ||
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/LogNormal.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/LogNormal.php
index d572d234f3..b051a8ddac 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/LogNormal.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/LogNormal.php
@@ -114,7 +114,7 @@ public static function distribution($value, $mean, $stdDev, $cumulative = false)
      *            accuracy if I can get my head round the mathematics
      *            (as described at) http://home.online.no/~pjacklam/notes/invnorm/
      */
-    public static function inverse($probability, $mean, $stdDev)
+    public static function inverse($probability, $mean, $stdDev): array|string|float
     {
         if (is_array($probability) || is_array($mean) || is_array($stdDev)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $probability, $mean, $stdDev);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/NewtonRaphson.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/NewtonRaphson.php
index d301407289..d1727f49d6 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/NewtonRaphson.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/NewtonRaphson.php
@@ -18,7 +18,7 @@ public function __construct(callable $callback)
     }
 
     /** @return float|string */
-    public function execute(float $probability)
+    public function execute(float $probability): string|int|float
     {
         $xLo = 100;
         $xHi = 0;
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Normal.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Normal.php
index 5715dacfaf..5fae0cb94c 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Normal.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Normal.php
@@ -33,7 +33,7 @@ class Normal
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value, $mean, $stdDev, $cumulative)
+    public static function distribution($value, $mean, $stdDev, $cumulative): array|string|float
     {
         if (is_array($value) || is_array($mean) || is_array($stdDev) || is_array($cumulative)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $mean, $stdDev, $cumulative);
@@ -75,7 +75,7 @@ public static function distribution($value, $mean, $stdDev, $cumulative)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function inverse($probability, $mean, $stdDev)
+    public static function inverse($probability, $mean, $stdDev): array|string|float
     {
         if (is_array($probability) || is_array($mean) || is_array($stdDev)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $probability, $mean, $stdDev);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Poisson.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Poisson.php
index 041c34a0fc..a8de2eb511 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Poisson.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Poisson.php
@@ -29,7 +29,7 @@ class Poisson
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value, $mean, $cumulative)
+    public static function distribution($value, $mean, $cumulative): array|string|float
     {
         if (is_array($value) || is_array($mean) || is_array($cumulative)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $mean, $cumulative);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StandardNormal.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StandardNormal.php
index 623146ca74..32d9dff9eb 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StandardNormal.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StandardNormal.php
@@ -94,7 +94,7 @@ public static function inverse($value)
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function gauss($value)
+    public static function gauss($value): array|string|float
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StudentT.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StudentT.php
index 9d89af6319..969901cefb 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StudentT.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/StudentT.php
@@ -88,10 +88,7 @@ public static function inverse($probability, $degrees)
         return $newtonRaphson->execute($probability);
     }
 
-    /**
-     * @return float
-     */
-    private static function calculateDistribution(float $value, int $degrees, int $tails)
+    private static function calculateDistribution(float $value, int $degrees, int $tails): float
     {
         //    tdist, which finds the probability that corresponds to a given value
         //    of t with k degrees of freedom. This algorithm is translated from a
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Weibull.php b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Weibull.php
index 51392c41f7..4de1155d8f 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Weibull.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Distributions/Weibull.php
@@ -29,7 +29,7 @@ class Weibull
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function distribution($value, $alpha, $beta, $cumulative)
+    public static function distribution($value, $alpha, $beta, $cumulative): array|string|float
     {
         if (is_array($value) || is_array($alpha) || is_array($beta) || is_array($cumulative)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $alpha, $beta, $cumulative);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Percentiles.php b/src/PhpSpreadsheet/Calculation/Statistical/Percentiles.php
index 4565ca442f..5f97d3947a 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Percentiles.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Percentiles.php
@@ -74,7 +74,7 @@ public static function PERCENTILE(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function PERCENTRANK($valueSet, $value, $significance = 3)
+    public static function PERCENTRANK($valueSet, $value, $significance = 3): string|float
     {
         $valueSet = Functions::flattenArray($valueSet);
         $value = Functions::flattenSingleValue($value);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Standardize.php b/src/PhpSpreadsheet/Calculation/Statistical/Standardize.php
index 51b0a51878..b8e73505c6 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Standardize.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Standardize.php
@@ -26,7 +26,7 @@ class Standardize extends StatisticalValidations
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function execute($value, $mean, $stdDev)
+    public static function execute($value, $mean, $stdDev): array|string|float
     {
         if (is_array($value) || is_array($mean) || is_array($stdDev)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $mean, $stdDev);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Trends.php b/src/PhpSpreadsheet/Calculation/Statistical/Trends.php
index 705de17d80..c44a8e2921 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Trends.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Trends.php
@@ -90,12 +90,12 @@ public static function CORREL($yValues, $xValues = null)
      *
      * Returns covariance, the average of the products of deviations for each data point pair.
      *
-     * @param mixed $yValues array of mixed Data Series Y
-     * @param mixed $xValues array of mixed Data Series X
+     * @param mixed[] $yValues array of mixed Data Series Y
+     * @param mixed[] $xValues array of mixed Data Series X
      *
      * @return float|string
      */
-    public static function COVAR($yValues, $xValues)
+    public static function COVAR(array $yValues, array $xValues)
     {
         try {
             self::checkTrendArrays($yValues, $xValues);
@@ -117,14 +117,14 @@ public static function COVAR($yValues, $xValues)
      *
      * @param mixed $xValue Float value of X for which we want to find Y
      *                      Or can be an array of values
-     * @param mixed $yValues array of mixed Data Series Y
-     * @param mixed $xValues of mixed Data Series X
+     * @param mixed[] $yValues array of mixed Data Series Y
+     * @param mixed[] $xValues array of mixed Data Series X
      *
      * @return array|bool|float|string
      *         If an array of numbers is passed as an argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function FORECAST($xValue, $yValues, $xValues)
+    public static function FORECAST($xValue, array $yValues, array $xValues)
     {
         if (is_array($xValue)) {
             return self::evaluateArrayArgumentsSubset([self::class, __FUNCTION__], 1, $xValue, $yValues, $xValues);
@@ -185,7 +185,7 @@ public static function GROWTH($yValues, $xValues = [], $newValues = [], $const =
      *
      * @return float|string
      */
-    public static function INTERCEPT($yValues, $xValues)
+    public static function INTERCEPT(array $yValues, array $xValues)
     {
         try {
             self::checkTrendArrays($yValues, $xValues);
@@ -210,9 +210,9 @@ public static function INTERCEPT($yValues, $xValues)
      * @param mixed $const A logical (boolean) value specifying whether to force the intersect to equal 0 or not
      * @param mixed $stats A logical (boolean) value specifying whether to return additional regression statistics
      *
-     * @return array|int|string The result, or a string containing an error
+     * @return array|string The result, or a string containing an error
      */
-    public static function LINEST($yValues, $xValues = null, $const = true, $stats = false)
+    public static function LINEST(array $yValues, $xValues = null, $const = true, $stats = false): string|array
     {
         $const = ($const === null) ? true : (bool) Functions::flattenSingleValue($const);
         $stats = ($stats === null) ? false : (bool) Functions::flattenSingleValue($stats);
@@ -271,9 +271,9 @@ public static function LINEST($yValues, $xValues = null, $const = true, $stats =
      * @param mixed $const A logical (boolean) value specifying whether to force the intersect to equal 0 or not
      * @param mixed $stats A logical (boolean) value specifying whether to return additional regression statistics
      *
-     * @return array|int|string The result, or a string containing an error
+     * @return array|string The result, or a string containing an error
      */
-    public static function LOGEST($yValues, $xValues = null, $const = true, $stats = false)
+    public static function LOGEST(array $yValues, $xValues = null, $const = true, $stats = false): string|array
     {
         $const = ($const === null) ? true : (bool) Functions::flattenSingleValue($const);
         $stats = ($stats === null) ? false : (bool) Functions::flattenSingleValue($stats);
@@ -338,7 +338,7 @@ public static function LOGEST($yValues, $xValues = null, $const = true, $stats =
      *
      * @return float|string The result, or a string containing an error
      */
-    public static function RSQ($yValues, $xValues)
+    public static function RSQ(array $yValues, array $xValues)
     {
         try {
             self::checkTrendArrays($yValues, $xValues);
@@ -362,7 +362,7 @@ public static function RSQ($yValues, $xValues)
      *
      * @return float|string The result, or a string containing an error
      */
-    public static function SLOPE($yValues, $xValues)
+    public static function SLOPE(array $yValues, array $xValues)
     {
         try {
             self::checkTrendArrays($yValues, $xValues);
@@ -386,7 +386,7 @@ public static function SLOPE($yValues, $xValues)
      *
      * @return float|string
      */
-    public static function STEYX($yValues, $xValues)
+    public static function STEYX(array $yValues, array $xValues)
     {
         try {
             self::checkTrendArrays($yValues, $xValues);
diff --git a/src/PhpSpreadsheet/Calculation/Statistical/Variances.php b/src/PhpSpreadsheet/Calculation/Statistical/Variances.php
index 938e671bfb..2204623eed 100644
--- a/src/PhpSpreadsheet/Calculation/Statistical/Variances.php
+++ b/src/PhpSpreadsheet/Calculation/Statistical/Variances.php
@@ -19,7 +19,7 @@ class Variances extends VarianceBase
      *
      * @return float|string (string if result is an error)
      */
-    public static function VAR(...$args)
+    public static function VAR(...$args): float|string
     {
         $returnValue = ExcelError::DIV0();
 
@@ -61,7 +61,7 @@ public static function VAR(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function VARA(...$args)
+    public static function VARA(...$args): string|float
     {
         $returnValue = ExcelError::DIV0();
 
@@ -107,7 +107,7 @@ public static function VARA(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function VARP(...$args)
+    public static function VARP(...$args): float|string
     {
         // Return value
         $returnValue = ExcelError::DIV0();
@@ -150,7 +150,7 @@ public static function VARP(...$args)
      *
      * @return float|string (string if result is an error)
      */
-    public static function VARPA(...$args)
+    public static function VARPA(...$args): string|float
     {
         $returnValue = ExcelError::DIV0();
 
diff --git a/src/PhpSpreadsheet/Calculation/TextData.php b/src/PhpSpreadsheet/Calculation/TextData.php
index 7cc1c70daf..61df9494d1 100644
--- a/src/PhpSpreadsheet/Calculation/TextData.php
+++ b/src/PhpSpreadsheet/Calculation/TextData.php
@@ -49,10 +49,8 @@ public static function TRIMNONPRINTABLE($stringValue = '')
      * @see TextData\Trim::spaces()
      *
      * @param mixed $stringValue Value to check
-     *
-     * @return array|string
      */
-    public static function TRIMSPACES($stringValue = '')
+    public static function TRIMSPACES($stringValue = ''): string|array
     {
         return TextData\Trim::spaces($stringValue);
     }
@@ -68,7 +66,7 @@ public static function TRIMSPACES($stringValue = '')
      *
      * @return array|int|string A string if arguments are invalid
      */
-    public static function ASCIICODE($characters)
+    public static function ASCIICODE($characters): string|int|array
     {
         return TextData\CharacterConvert::code($characters);
     }
@@ -81,10 +79,8 @@ public static function ASCIICODE($characters)
      * @see TextData\Concatenate::CONCATENATE()
      *
      * @param array $args
-     *
-     * @return string
      */
-    public static function CONCATENATE(...$args)
+    public static function CONCATENATE(...$args): string
     {
         return TextData\Concatenate::CONCATENATE(...$args);
     }
@@ -174,10 +170,8 @@ public static function FIXEDFORMAT($value, $decimals = 2, $no_commas = false)
      *
      * @param array|string $value Value
      * @param array|int $chars Number of characters
-     *
-     * @return array|string
      */
-    public static function LEFT($value = '', $chars = 1)
+    public static function LEFT($value = '', $chars = 1): string|array
     {
         return TextData\Extract::left($value, $chars);
     }
@@ -192,10 +186,8 @@ public static function LEFT($value = '', $chars = 1)
      * @param array|string $value Value
      * @param array|int $start Start character
      * @param array|int $chars Number of characters
-     *
-     * @return array|string
      */
-    public static function MID($value = '', $start = 1, $chars = null)
+    public static function MID($value = '', $start = 1, $chars = null): string|array
     {
         return TextData\Extract::mid($value, $start, $chars);
     }
@@ -209,10 +201,8 @@ public static function MID($value = '', $start = 1, $chars = null)
      *
      * @param array|string $value Value
      * @param array|int $chars Number of characters
-     *
-     * @return array|string
      */
-    public static function RIGHT($value = '', $chars = 1)
+    public static function RIGHT($value = '', $chars = 1): string|array
     {
         return TextData\Extract::right($value, $chars);
     }
@@ -225,10 +215,8 @@ public static function RIGHT($value = '', $chars = 1)
      * @see TextData\Text::length()
      *
      * @param string $value Value
-     *
-     * @return array|int
      */
-    public static function STRINGLENGTH($value = '')
+    public static function STRINGLENGTH($value = ''): int|array
     {
         return TextData\Text::length($value);
     }
@@ -243,10 +231,8 @@ public static function STRINGLENGTH($value = '')
      * @see TextData\CaseConvert::lower()
      *
      * @param array|string $mixedCaseString
-     *
-     * @return array|string
      */
-    public static function LOWERCASE($mixedCaseString)
+    public static function LOWERCASE($mixedCaseString): string|array
     {
         return TextData\CaseConvert::lower($mixedCaseString);
     }
@@ -261,10 +247,8 @@ public static function LOWERCASE($mixedCaseString)
      * @see TextData\CaseConvert::upper()
      *
      * @param string $mixedCaseString
-     *
-     * @return array|string
      */
-    public static function UPPERCASE($mixedCaseString)
+    public static function UPPERCASE($mixedCaseString): string|array
     {
         return TextData\CaseConvert::upper($mixedCaseString);
     }
@@ -279,10 +263,8 @@ public static function UPPERCASE($mixedCaseString)
      * @see TextData\CaseConvert::proper()
      *
      * @param array|string $mixedCaseString
-     *
-     * @return array|string
      */
-    public static function PROPERCASE($mixedCaseString)
+    public static function PROPERCASE($mixedCaseString): string|array
     {
         return TextData\CaseConvert::proper($mixedCaseString);
     }
@@ -333,10 +315,8 @@ public static function SUBSTITUTE($text = '', $fromText = '', $toText = '', $ins
      * @see TextData\Text::test()
      *
      * @param mixed $testValue Value to check
-     *
-     * @return null|array|string
      */
-    public static function RETURNSTRING($testValue = '')
+    public static function RETURNSTRING($testValue = ''): string|array
     {
         return TextData\Text::test($testValue);
     }
@@ -403,10 +383,8 @@ public static function NUMBERVALUE($value = '', $decimalSeparator = null, $group
      *
      * @param mixed $value1
      * @param mixed $value2
-     *
-     * @return array|bool
      */
-    public static function EXACT($value1, $value2)
+    public static function EXACT($value1, $value2): bool|array
     {
         return TextData\Text::exact($value1, $value2);
     }
diff --git a/src/PhpSpreadsheet/Calculation/TextData/CaseConvert.php b/src/PhpSpreadsheet/Calculation/TextData/CaseConvert.php
index f1aea16940..a80c5dd60e 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/CaseConvert.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/CaseConvert.php
@@ -21,7 +21,7 @@ class CaseConvert
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function lower($mixedCaseValue)
+    public static function lower($mixedCaseValue): array|string
     {
         if (is_array($mixedCaseValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $mixedCaseValue);
@@ -44,7 +44,7 @@ public static function lower($mixedCaseValue)
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function upper($mixedCaseValue)
+    public static function upper($mixedCaseValue): array|string
     {
         if (is_array($mixedCaseValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $mixedCaseValue);
@@ -67,7 +67,7 @@ public static function upper($mixedCaseValue)
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function proper($mixedCaseValue)
+    public static function proper($mixedCaseValue): array|string
     {
         if (is_array($mixedCaseValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $mixedCaseValue);
diff --git a/src/PhpSpreadsheet/Calculation/TextData/CharacterConvert.php b/src/PhpSpreadsheet/Calculation/TextData/CharacterConvert.php
index 83af499bbf..4b8ab6e29c 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/CharacterConvert.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/CharacterConvert.php
@@ -20,7 +20,7 @@ class CharacterConvert
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function character($character)
+    public static function character($character): array|string
     {
         if (is_array($character)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $character);
@@ -46,7 +46,7 @@ public static function character($character)
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function code($characters)
+    public static function code($characters): array|string|int
     {
         if (is_array($characters)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $characters);
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Concatenate.php b/src/PhpSpreadsheet/Calculation/TextData/Concatenate.php
index 37c135df2f..df5167de21 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Concatenate.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Concatenate.php
@@ -56,7 +56,7 @@ public static function CONCATENATE(...$args): string
      *         If an array of values is passed for the $delimiter or $ignoreEmpty arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function TEXTJOIN($delimiter = '', $ignoreEmpty = true, ...$args)
+    public static function TEXTJOIN($delimiter = '', $ignoreEmpty = true, ...$args): array|string
     {
         if (is_array($delimiter) || is_array($ignoreEmpty)) {
             return self::evaluateArrayArgumentsSubset(
@@ -113,7 +113,7 @@ private static function evaluateTextJoinArray(bool $ignoreEmpty, array &$aArgs):
      *         If an array of values is passed for the $stringValue or $repeatCount arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function builtinREPT($stringValue, $repeatCount)
+    public static function builtinREPT($stringValue, $repeatCount): array|string
     {
         if (is_array($stringValue) || is_array($repeatCount)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $stringValue, $repeatCount);
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Extract.php b/src/PhpSpreadsheet/Calculation/TextData/Extract.php
index 24ddff2ec5..2dc46b02a7 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Extract.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Extract.php
@@ -24,7 +24,7 @@ class Extract
      *         If an array of values is passed for the $value or $chars arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function left($value, $chars = 1)
+    public static function left($value, $chars = 1): array|string
     {
         if (is_array($value) || is_array($chars)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $chars);
@@ -54,7 +54,7 @@ public static function left($value, $chars = 1)
      *         If an array of values is passed for the $value, $start or $chars arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function mid($value, $start, $chars)
+    public static function mid($value, $start, $chars): array|string
     {
         if (is_array($value) || is_array($start) || is_array($chars)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $start, $chars);
@@ -83,7 +83,7 @@ public static function mid($value, $start, $chars)
      *         If an array of values is passed for the $value or $chars arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function right($value, $chars = 1)
+    public static function right($value, $chars = 1): array|string
     {
         if (is_array($value) || is_array($chars)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $chars);
@@ -122,11 +122,11 @@ public static function right($value, $chars = 1)
      *                             The default is a #N/A Error
      *                          Or can be an array of values
      *
-     * @return mixed|mixed[] the string extracted from text before the delimiter; or the $ifNotFound value
+     * @return array|string the string extracted from text before the delimiter; or the $ifNotFound value
      *         If an array of values is passed for any of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function before($text, $delimiter, $instance = 1, $matchMode = 0, $matchEnd = 0, $ifNotFound = '#N/A')
+    public static function before($text, $delimiter, $instance = 1, $matchMode = 0, $matchEnd = 0, $ifNotFound = '#N/A'): array|string
     {
         if (is_array($text) || is_array($instance) || is_array($matchMode) || is_array($matchEnd) || is_array($ifNotFound)) {
             return self::evaluateArrayArgumentsIgnore([self::class, __FUNCTION__], 1, $text, $delimiter, $instance, $matchMode, $matchEnd, $ifNotFound);
@@ -180,11 +180,11 @@ public static function before($text, $delimiter, $instance = 1, $matchMode = 0,
      *                             The default is a #N/A Error
      *                          Or can be an array of values
      *
-     * @return mixed|mixed[] the string extracted from text before the delimiter; or the $ifNotFound value
+     * @return array|string the string extracted from text before the delimiter; or the $ifNotFound value
      *         If an array of values is passed for any of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function after($text, $delimiter, $instance = 1, $matchMode = 0, $matchEnd = 0, $ifNotFound = '#N/A')
+    public static function after($text, $delimiter, $instance = 1, $matchMode = 0, $matchEnd = 0, $ifNotFound = '#N/A'): array|string
     {
         if (is_array($text) || is_array($instance) || is_array($matchMode) || is_array($matchEnd) || is_array($ifNotFound)) {
             return self::evaluateArrayArgumentsIgnore([self::class, __FUNCTION__], 1, $text, $delimiter, $instance, $matchMode, $matchEnd, $ifNotFound);
@@ -218,13 +218,12 @@ public static function after($text, $delimiter, $instance = 1, $matchMode = 0, $
 
     /**
      * @param null|array|string $delimiter
-     * @param int $matchMode
      * @param int $matchEnd
      * @param mixed $ifNotFound
      *
      * @return array|string
      */
-    private static function validateTextBeforeAfter(string $text, $delimiter, int $instance, $matchMode, $matchEnd, $ifNotFound)
+    private static function validateTextBeforeAfter(string $text, $delimiter, int $instance, int $matchMode, $matchEnd, $ifNotFound)
     {
         $flags = self::matchFlags($matchMode);
         $delimiter = self::buildDelimiter($delimiter);
@@ -260,7 +259,7 @@ private static function buildDelimiter($delimiter): string
         if (is_array($delimiter)) {
             $delimiter = Functions::flattenArray($delimiter);
             $quotedDelimiters = array_map(
-                function ($delimiter) {
+                function ($delimiter): string {
                     return preg_quote($delimiter ?? '', '/');
                 },
                 $delimiter
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Format.php b/src/PhpSpreadsheet/Calculation/TextData/Format.php
index 57d3316637..55e0a4710f 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Format.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Format.php
@@ -78,7 +78,7 @@ public static function DOLLAR($value = 0, $decimals = 2)
      *         If an array of values is passed for either of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function FIXEDFORMAT($value, $decimals = 2, $noCommas = false)
+    public static function FIXEDFORMAT($value, $decimals = 2, $noCommas = false): array|string
     {
         if (is_array($value) || is_array($decimals) || is_array($noCommas)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $decimals, $noCommas);
@@ -119,7 +119,7 @@ public static function FIXEDFORMAT($value, $decimals = 2, $noCommas = false)
      *         If an array of values is passed for either of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function TEXTFORMAT($value, $format)
+    public static function TEXTFORMAT($value, $format): array|string
     {
         if (is_array($value) || is_array($format)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $format);
@@ -230,7 +230,7 @@ public static function VALUE($value = '')
      *         If an array of values is passed for either of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function valueToText($value, $format = false)
+    public static function valueToText($value, $format = false): array|string
     {
         if (is_array($value) || is_array($format)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $format);
@@ -276,10 +276,8 @@ private static function getGroupSeparator($groupSeparator): string
      *                         Or can be an array of values
      * @param mixed $groupSeparator A string with the group/thousands separator to use, defaults to locale defined value
      *                         Or can be an array of values
-     *
-     * @return array|float|string
      */
-    public static function NUMBERVALUE($value = '', $decimalSeparator = null, $groupSeparator = null)
+    public static function NUMBERVALUE($value = '', $decimalSeparator = null, $groupSeparator = null): array|string|float
     {
         if (is_array($value) || is_array($decimalSeparator) || is_array($groupSeparator)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value, $decimalSeparator, $groupSeparator);
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Replace.php b/src/PhpSpreadsheet/Calculation/TextData/Replace.php
index 124f001703..e10f5b8bb6 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Replace.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Replace.php
@@ -29,7 +29,7 @@ class Replace
      *         If an array of values is passed for either of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function replace($oldText, $start, $chars, $newText)
+    public static function replace($oldText, $start, $chars, $newText): array|string
     {
         if (is_array($oldText) || is_array($start) || is_array($chars) || is_array($newText)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $oldText, $start, $chars, $newText);
@@ -70,7 +70,7 @@ public static function replace($oldText, $start, $chars, $newText)
      *         If an array of values is passed for either of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function substitute($text = '', $fromText = '', $toText = '', $instance = null)
+    public static function substitute($text = '', $fromText = '', $toText = '', $instance = null): array|string
     {
         if (is_array($text) || is_array($fromText) || is_array($toText) || is_array($instance)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $text, $fromText, $toText, $instance);
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Search.php b/src/PhpSpreadsheet/Calculation/TextData/Search.php
index 10b6a1aadf..8eecf1679b 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Search.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Search.php
@@ -25,7 +25,7 @@ class Search
      *         If an array of values is passed for the $value or $chars arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function sensitive($needle, $haystack, $offset = 1)
+    public static function sensitive($needle, $haystack, $offset = 1): array|string|int
     {
         if (is_array($needle) || is_array($haystack) || is_array($offset)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $needle, $haystack, $offset);
@@ -67,7 +67,7 @@ public static function sensitive($needle, $haystack, $offset = 1)
      *         If an array of values is passed for the $value or $chars arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function insensitive($needle, $haystack, $offset = 1)
+    public static function insensitive($needle, $haystack, $offset = 1): array|string|int
     {
         if (is_array($needle) || is_array($haystack) || is_array($offset)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $needle, $haystack, $offset);
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Text.php b/src/PhpSpreadsheet/Calculation/TextData/Text.php
index b8a730767c..2d49c00976 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Text.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Text.php
@@ -21,7 +21,7 @@ class Text
      *         If an array of values is passed for the argument, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function length($value = '')
+    public static function length($value = ''): array|int
     {
         if (is_array($value)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $value);
@@ -46,7 +46,7 @@ public static function length($value = '')
      *         If an array of values is passed for either of the arguments, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function exact($value1, $value2)
+    public static function exact($value1, $value2): array|bool
     {
         if (is_array($value1) || is_array($value2)) {
             return self::evaluateArrayArguments([self::class, __FUNCTION__], $value1, $value2);
@@ -68,7 +68,7 @@ public static function exact($value1, $value2)
      *         If an array of values is passed for the argument, then the returned result
      *            will also be an array with matching dimensions
      */
-    public static function test($testValue = '')
+    public static function test($testValue = ''): array|string
     {
         if (is_array($testValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $testValue);
@@ -102,7 +102,7 @@ public static function test($testValue = '')
      *
      * @return array the array built from the text, split by the row and column delimiters
      */
-    public static function split($text, $columnDelimiter = null, $rowDelimiter = null, bool $ignoreEmpty = false, bool $matchMode = true, $padding = '#N/A')
+    public static function split($text, $columnDelimiter = null, $rowDelimiter = null, bool $ignoreEmpty = false, bool $matchMode = true, $padding = '#N/A'): array
     {
         $text = Functions::flattenSingleValue($text);
 
@@ -121,7 +121,7 @@ public static function split($text, $columnDelimiter = null, $rowDelimiter = nul
         if ($ignoreEmpty === true) {
             $rows = array_values(array_filter(
                 $rows,
-                function ($row) {
+                function ($row): bool {
                     return $row !== '';
                 }
             ));
@@ -139,7 +139,7 @@ function (&$row) use ($delimiter, $flags, $ignoreEmpty): void {
                     if ($ignoreEmpty === true) {
                         $row = array_values(array_filter(
                             $row,
-                            function ($value) {
+                            function ($value): bool {
                                 return $value !== '';
                             }
                         ));
@@ -149,7 +149,7 @@ function ($value) {
             if ($ignoreEmpty === true) {
                 $rows = array_values(array_filter(
                     $rows,
-                    function ($row) {
+                    function ($row): bool {
                         return $row !== [] && $row !== [''];
                     }
                 ));
@@ -192,7 +192,7 @@ private static function buildDelimiter($delimiter): string
 
         if (is_array($delimiter) && count($valueSet) > 1) {
             $quotedDelimiters = array_map(
-                function ($delimiter) {
+                function ($delimiter): string {
                     return preg_quote($delimiter ?? '', '/');
                 },
                 $valueSet
@@ -239,10 +239,7 @@ private static function formatValueMode0($cellValue): string
         return (string) $cellValue;
     }
 
-    /**
-     * @param mixed $cellValue
-     */
-    private static function formatValueMode1($cellValue): string
+    private static function formatValueMode1(mixed $cellValue): string
     {
         if (is_string($cellValue) && ErrorValue::isError($cellValue) === false) {
             return Calculation::FORMULA_STRING_QUOTE . $cellValue . Calculation::FORMULA_STRING_QUOTE;
diff --git a/src/PhpSpreadsheet/Calculation/TextData/Trim.php b/src/PhpSpreadsheet/Calculation/TextData/Trim.php
index 27eceb9388..96c29d1d49 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Trim.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Trim.php
@@ -39,7 +39,7 @@ public static function nonPrintable($stringValue = '')
      *         If an array of values is passed as the argument, then the returned result will also be an array
      *            with the same dimensions
      */
-    public static function spaces($stringValue = '')
+    public static function spaces($stringValue = ''): array|string
     {
         if (is_array($stringValue)) {
             return self::evaluateSingleArgumentArray([self::class, __FUNCTION__], $stringValue);
diff --git a/src/PhpSpreadsheet/Calculation/Token/Stack.php b/src/PhpSpreadsheet/Calculation/Token/Stack.php
index e8289e3fb6..ae3ab2fe96 100644
--- a/src/PhpSpreadsheet/Calculation/Token/Stack.php
+++ b/src/PhpSpreadsheet/Calculation/Token/Stack.php
@@ -7,10 +7,7 @@
 
 class Stack
 {
-    /**
-     * @var BranchPruner
-     */
-    private $branchPruner;
+    private BranchPruner $branchPruner;
 
     /**
      * The parser stack for formulae.
diff --git a/src/PhpSpreadsheet/Calculation/Web/Service.php b/src/PhpSpreadsheet/Calculation/Web/Service.php
index 697d3a6143..3b1bea945e 100644
--- a/src/PhpSpreadsheet/Calculation/Web/Service.php
+++ b/src/PhpSpreadsheet/Calculation/Web/Service.php
@@ -64,7 +64,7 @@ public static function webService(string $url)
      *
      * @return string the url encoded output
      */
-    public static function urlEncode($text)
+    public static function urlEncode($text): string|array
     {
         if (!is_string($text)) {
             return ExcelError::VALUE();
diff --git a/src/PhpSpreadsheet/Cell/AddressHelper.php b/src/PhpSpreadsheet/Cell/AddressHelper.php
index ed765aa594..98b8e27c43 100644
--- a/src/PhpSpreadsheet/Cell/AddressHelper.php
+++ b/src/PhpSpreadsheet/Cell/AddressHelper.php
@@ -11,7 +11,7 @@ class AddressHelper
     public const R1C1_COORDINATE_REGEX = '/(R((?:\[-?\d*\])|(?:\d*))?)(C((?:\[-?\d*\])|(?:\d*))?)/i';
 
     /** @return string[] */
-    public static function getRowAndColumnChars()
+    public static function getRowAndColumnChars(): array
     {
         $rowChar = 'R';
         $colChar = 'C';
diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index 36f27a27ae..6a532892b5 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -45,17 +45,15 @@ class Cell
 
     /**
      * Type of the cell data.
-     *
-     * @var string
      */
-    private $dataType;
+    private string $dataType;
 
     /**
      * The collection of cells that this cell belongs to (i.e. The Cell Collection for the parent Worksheet).
      *
      * @var ?Cells
      */
-    private $parent;
+    private ?Cells $parent;
 
     /**
      * Index to the cellXf reference for the styling of this cell.
@@ -71,8 +69,7 @@ class Cell
      */
     private $formulaAttributes;
 
-    /** @var IgnoredErrors */
-    private $ignoredErrors;
+    private IgnoredErrors $ignoredErrors;
 
     /**
      * Update the cell into the cell collection.
@@ -127,10 +124,8 @@ public function __construct($value, ?string $dataType, Worksheet $worksheet)
 
     /**
      * Get cell coordinate column.
-     *
-     * @return string
      */
-    public function getColumn()
+    public function getColumn(): string
     {
         $parent = $this->parent;
         if ($parent === null) {
@@ -142,10 +137,8 @@ public function getColumn()
 
     /**
      * Get cell coordinate row.
-     *
-     * @return int
      */
-    public function getRow()
+    public function getRow(): int
     {
         $parent = $this->parent;
         if ($parent === null) {
@@ -790,10 +783,8 @@ public function getFormulaAttributes()
 
     /**
      * Convert to string.
-     *
-     * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->getValue();
     }
diff --git a/src/PhpSpreadsheet/Cell/CellAddress.php b/src/PhpSpreadsheet/Cell/CellAddress.php
index a0c544f284..a5db0c2177 100644
--- a/src/PhpSpreadsheet/Cell/CellAddress.php
+++ b/src/PhpSpreadsheet/Cell/CellAddress.php
@@ -7,30 +7,15 @@
 
 class CellAddress
 {
-    /**
-     * @var ?Worksheet
-     */
-    protected $worksheet;
+    protected ?Worksheet $worksheet;
 
-    /**
-     * @var string
-     */
-    protected $cellAddress;
+    protected string $cellAddress;
 
-    /**
-     * @var string
-     */
-    protected $columnName;
+    protected string $columnName = '';
 
-    /**
-     * @var int
-     */
-    protected $columnId;
+    protected int $columnId;
 
-    /**
-     * @var int
-     */
-    protected $rowId;
+    protected int $rowId;
 
     public function __construct(string $cellAddress, ?Worksheet $worksheet = null)
     {
@@ -159,7 +144,7 @@ public function previousColumn(int $offset = 1): self
      *     (ie. if a Worksheet was provided to the constructor).
      *     e.g. "'Mark''s Worksheet'!C5".
      */
-    public function __toString()
+    public function __toString(): string
     {
         return $this->fullCellAddress();
     }
diff --git a/src/PhpSpreadsheet/Cell/ColumnRange.php b/src/PhpSpreadsheet/Cell/ColumnRange.php
index 1e521a1319..a5e256f974 100644
--- a/src/PhpSpreadsheet/Cell/ColumnRange.php
+++ b/src/PhpSpreadsheet/Cell/ColumnRange.php
@@ -6,20 +6,11 @@
 
 class ColumnRange implements AddressRange
 {
-    /**
-     * @var ?Worksheet
-     */
-    protected $worksheet;
+    protected ?Worksheet $worksheet;
 
-    /**
-     * @var int
-     */
-    protected $from;
+    protected int $from;
 
-    /**
-     * @var int
-     */
-    protected $to;
+    protected int $to;
 
     public function __construct(string $from, ?string $to = null, ?Worksheet $worksheet = null)
     {
diff --git a/src/PhpSpreadsheet/Cell/Coordinate.php b/src/PhpSpreadsheet/Cell/Coordinate.php
index a89de85bd1..9f4df6d7e0 100644
--- a/src/PhpSpreadsheet/Cell/Coordinate.php
+++ b/src/PhpSpreadsheet/Cell/Coordinate.php
@@ -29,7 +29,7 @@ abstract class Coordinate
      *
      * @return array{0: string, 1: string} Array containing column and row (indexes 0 and 1)
      */
-    public static function coordinateFromString($cellAddress): array
+    public static function coordinateFromString(string $cellAddress): array
     {
         if (preg_match(self::A1_COORDINATE_REGEX, $cellAddress, $matches)) {
             return [$matches['col'], $matches['row']];
@@ -68,7 +68,7 @@ public static function indexesFromString(string $coordinates): array
      *
      * @return bool Whether the coordinate represents a range of cells
      */
-    public static function coordinateIsRange($cellAddress)
+    public static function coordinateIsRange($cellAddress): bool
     {
         return (strpos($cellAddress, ':') !== false) || (strpos($cellAddress, ',') !== false);
     }
@@ -111,7 +111,7 @@ public static function absoluteReference($cellAddress)
      *
      * @return string Absolute coordinate        e.g. '$A$1'
      */
-    public static function absoluteCoordinate($cellAddress)
+    public static function absoluteCoordinate(string $cellAddress)
     {
         if (self::coordinateIsRange($cellAddress)) {
             throw new Exception('Cell coordinate string can not be a range of cells');
@@ -124,7 +124,7 @@ public static function absoluteCoordinate($cellAddress)
         }
 
         // Create absolute coordinate
-        [$column, $row] = self::coordinateFromString($cellAddress);
+        [$column, $row] = self::coordinateFromString($cellAddress); // @phpstan-ignore-line
         $column = ltrim($column, '$');
         $row = ltrim($row, '$');
 
@@ -233,7 +233,7 @@ public static function rangeBoundaries(string $range): array
      *
      * @return array Range dimension (width, height)
      */
-    public static function rangeDimension($range)
+    public static function rangeDimension(string $range)
     {
         // Calculate range outer borders
         [$rangeStart, $rangeEnd] = self::rangeBoundaries($range);
@@ -249,7 +249,7 @@ public static function rangeDimension($range)
      * @return array Range coordinates [Start Cell, End Cell]
      *                    where Start Cell and End Cell are arrays [Column ID, Row Number]
      */
-    public static function getRangeBoundaries($range)
+    public static function getRangeBoundaries(string $range)
     {
         [$rangeA, $rangeB] = self::rangeBoundaries($range);
 
@@ -266,7 +266,7 @@ public static function getRangeBoundaries($range)
      *
      * @return int Column index (A = 1)
      */
-    public static function columnIndexFromString($columnAddress)
+    public static function columnIndexFromString(?string $columnAddress): int
     {
         //    Using a lookup cache adds a slight memory overhead, but boosts speed
         //    caching using a static within the method is faster than a class static,
@@ -356,14 +356,14 @@ public static function extractAllCellReferencesInRange($cellRange): array
 
         [$worksheet, $cellRange] = Worksheet::extractSheetTitle($cellRange, true);
         $quoted = '';
-        if ($worksheet > '') {
+        if ($worksheet) {
             $quoted = Worksheet::nameRequiresQuotes($worksheet) ? "'" : '';
             if (substr($worksheet, 0, 1) === "'" && substr($worksheet, -1, 1) === "'") {
                 $worksheet = substr($worksheet, 1, -1);
             }
             $worksheet = str_replace("'", "''", $worksheet);
         }
-        [$ranges, $operators] = self::getCellBlocksFromRangeString($cellRange);
+        [$ranges, $operators] = self::getCellBlocksFromRangeString($cellRange); // @phpstan-ignore-line
 
         $cells = [];
         foreach ($ranges as $range) {
@@ -594,7 +594,7 @@ private static function getCellBlocksFromRangeString($rangeString)
      * @param int $currentRow
      * @param int $endRow
      */
-    private static function validateRange($cellBlock, $startColumnIndex, $endColumnIndex, $currentRow, $endRow): void
+    private static function validateRange(string $cellBlock, $startColumnIndex, $endColumnIndex, $currentRow, $endRow): void
     {
         if ($startColumnIndex >= $endColumnIndex || $currentRow > $endRow) {
             throw new Exception('Invalid range: "' . $cellBlock . '"');
diff --git a/src/PhpSpreadsheet/Cell/DataType.php b/src/PhpSpreadsheet/Cell/DataType.php
index f19984db6a..501475441a 100644
--- a/src/PhpSpreadsheet/Cell/DataType.php
+++ b/src/PhpSpreadsheet/Cell/DataType.php
@@ -53,7 +53,7 @@ public static function getErrorCodes()
      *
      * @return RichText|string Sanitized value
      */
-    public static function checkString($textValue)
+    public static function checkString($textValue): RichText|string|array
     {
         if ($textValue instanceof RichText) {
             // TODO: Sanitize Rich-Text string (max. character count is 32,767)
@@ -76,7 +76,7 @@ public static function checkString($textValue)
      *
      * @return string Sanitized value
      */
-    public static function checkErrorCode($value)
+    public static function checkErrorCode($value): string
     {
         $value = (string) $value;
 
diff --git a/src/PhpSpreadsheet/Cell/DataValidation.php b/src/PhpSpreadsheet/Cell/DataValidation.php
index 7ee53eae07..21d41c8dc3 100644
--- a/src/PhpSpreadsheet/Cell/DataValidation.php
+++ b/src/PhpSpreadsheet/Cell/DataValidation.php
@@ -144,7 +144,7 @@ public function getFormula1()
      *
      * @return $this
      */
-    public function setFormula1($formula)
+    public function setFormula1($formula): static
     {
         $this->formula1 = $formula;
 
@@ -168,7 +168,7 @@ public function getFormula2()
      *
      * @return $this
      */
-    public function setFormula2($formula)
+    public function setFormula2($formula): static
     {
         $this->formula2 = $formula;
 
@@ -192,7 +192,7 @@ public function getType()
      *
      * @return $this
      */
-    public function setType($type)
+    public function setType($type): static
     {
         $this->type = $type;
 
@@ -216,7 +216,7 @@ public function getErrorStyle()
      *
      * @return $this
      */
-    public function setErrorStyle($errorStyle)
+    public function setErrorStyle($errorStyle): static
     {
         $this->errorStyle = $errorStyle;
 
@@ -240,7 +240,7 @@ public function getOperator()
      *
      * @return $this
      */
-    public function setOperator($operator)
+    public function setOperator($operator): static
     {
         $this->operator = $operator;
 
@@ -264,7 +264,7 @@ public function getAllowBlank()
      *
      * @return $this
      */
-    public function setAllowBlank($allowBlank)
+    public function setAllowBlank($allowBlank): static
     {
         $this->allowBlank = $allowBlank;
 
@@ -288,7 +288,7 @@ public function getShowDropDown()
      *
      * @return $this
      */
-    public function setShowDropDown($showDropDown)
+    public function setShowDropDown($showDropDown): static
     {
         $this->showDropDown = $showDropDown;
 
@@ -312,7 +312,7 @@ public function getShowInputMessage()
      *
      * @return $this
      */
-    public function setShowInputMessage($showInputMessage)
+    public function setShowInputMessage($showInputMessage): static
     {
         $this->showInputMessage = $showInputMessage;
 
@@ -336,7 +336,7 @@ public function getShowErrorMessage()
      *
      * @return $this
      */
-    public function setShowErrorMessage($showErrorMessage)
+    public function setShowErrorMessage($showErrorMessage): static
     {
         $this->showErrorMessage = $showErrorMessage;
 
@@ -360,7 +360,7 @@ public function getErrorTitle()
      *
      * @return $this
      */
-    public function setErrorTitle($errorTitle)
+    public function setErrorTitle($errorTitle): static
     {
         $this->errorTitle = $errorTitle;
 
@@ -384,7 +384,7 @@ public function getError()
      *
      * @return $this
      */
-    public function setError($error)
+    public function setError($error): static
     {
         $this->error = $error;
 
@@ -408,7 +408,7 @@ public function getPromptTitle()
      *
      * @return $this
      */
-    public function setPromptTitle($promptTitle)
+    public function setPromptTitle($promptTitle): static
     {
         $this->promptTitle = $promptTitle;
 
@@ -432,7 +432,7 @@ public function getPrompt()
      *
      * @return $this
      */
-    public function setPrompt($prompt)
+    public function setPrompt($prompt): static
     {
         $this->prompt = $prompt;
 
@@ -444,7 +444,7 @@ public function setPrompt($prompt)
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->formula1 .
@@ -480,8 +480,7 @@ public function __clone()
         }
     }
 
-    /** @var ?string */
-    private $sqref;
+    private ?string $sqref = null;
 
     public function getSqref(): ?string
     {
diff --git a/src/PhpSpreadsheet/Cell/DataValidator.php b/src/PhpSpreadsheet/Cell/DataValidator.php
index 692f316ec0..90f0fce61b 100644
--- a/src/PhpSpreadsheet/Cell/DataValidator.php
+++ b/src/PhpSpreadsheet/Cell/DataValidator.php
@@ -15,10 +15,8 @@ class DataValidator
      * Does this cell contain valid value?
      *
      * @param Cell $cell Cell to check the value
-     *
-     * @return bool
      */
-    public function isValid(Cell $cell)
+    public function isValid(Cell $cell): bool
     {
         if (!$cell->hasDataValidation() || $cell->getDataValidation()->getType() === DataValidation::TYPE_NONE) {
             return true;
@@ -54,8 +52,7 @@ public function isValid(Cell $cell)
         return $returnValue;
     }
 
-    /** @param float|int $cellValue */
-    private function numericOperator(DataValidation $dataValidation, $cellValue): bool
+    private function numericOperator(DataValidation $dataValidation, int|float $cellValue): bool
     {
         $operator = $dataValidation->getOperator();
         $formula1 = $dataValidation->getFormula1();
@@ -86,10 +83,8 @@ private function numericOperator(DataValidation $dataValidation, $cellValue): bo
      * Does this cell contain valid value, based on list?
      *
      * @param Cell $cell Cell to check the value
-     *
-     * @return bool
      */
-    private function isValueInList(Cell $cell)
+    private function isValueInList(Cell $cell): bool
     {
         $cellValue = $cell->getValue();
         $dataValidation = $cell->getDataValidation();
diff --git a/src/PhpSpreadsheet/Cell/Hyperlink.php b/src/PhpSpreadsheet/Cell/Hyperlink.php
index ffdcbacd27..14f3644611 100644
--- a/src/PhpSpreadsheet/Cell/Hyperlink.php
+++ b/src/PhpSpreadsheet/Cell/Hyperlink.php
@@ -48,7 +48,7 @@ public function getUrl()
      *
      * @return $this
      */
-    public function setUrl($url)
+    public function setUrl($url): static
     {
         $this->url = $url;
 
@@ -72,7 +72,7 @@ public function getTooltip()
      *
      * @return $this
      */
-    public function setTooltip($tooltip)
+    public function setTooltip($tooltip): static
     {
         $this->tooltip = $tooltip;
 
@@ -81,18 +81,13 @@ public function setTooltip($tooltip)
 
     /**
      * Is this hyperlink internal? (to another worksheet).
-     *
-     * @return bool
      */
-    public function isInternal()
+    public function isInternal(): bool
     {
         return strpos($this->url, 'sheet://') !== false;
     }
 
-    /**
-     * @return string
-     */
-    public function getTypeHyperlink()
+    public function getTypeHyperlink(): string
     {
         return $this->isInternal() ? '' : 'External';
     }
@@ -102,7 +97,7 @@ public function getTypeHyperlink()
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->url .
diff --git a/src/PhpSpreadsheet/Cell/RowRange.php b/src/PhpSpreadsheet/Cell/RowRange.php
index 38e6c1415b..61c82dd250 100644
--- a/src/PhpSpreadsheet/Cell/RowRange.php
+++ b/src/PhpSpreadsheet/Cell/RowRange.php
@@ -6,20 +6,11 @@
 
 class RowRange implements AddressRange
 {
-    /**
-     * @var ?Worksheet
-     */
-    protected $worksheet;
-
-    /**
-     * @var int
-     */
-    protected $from;
-
-    /**
-     * @var int
-     */
-    protected $to;
+    protected ?Worksheet $worksheet;
+
+    protected int $from;
+
+    protected int $to;
 
     public function __construct(int $from, ?int $to = null, ?Worksheet $worksheet = null)
     {
diff --git a/src/PhpSpreadsheet/Cell/StringValueBinder.php b/src/PhpSpreadsheet/Cell/StringValueBinder.php
index 1dcb6129c7..5250213753 100644
--- a/src/PhpSpreadsheet/Cell/StringValueBinder.php
+++ b/src/PhpSpreadsheet/Cell/StringValueBinder.php
@@ -77,7 +77,7 @@ public function setConversionForAllValueTypes(bool $suppressConversion = false):
      * @param Cell $cell Cell to bind value to
      * @param mixed $value Value to bind in cell
      */
-    public function bindValue(Cell $cell, $value)
+    public function bindValue(Cell $cell, $value): bool
     {
         if (is_object($value)) {
             return $this->bindObjectValue($cell, $value);
diff --git a/src/PhpSpreadsheet/CellReferenceHelper.php b/src/PhpSpreadsheet/CellReferenceHelper.php
index 6e036354f0..2bb0c8a2df 100644
--- a/src/PhpSpreadsheet/CellReferenceHelper.php
+++ b/src/PhpSpreadsheet/CellReferenceHelper.php
@@ -7,30 +7,15 @@
 
 class CellReferenceHelper
 {
-    /**
-     * @var string
-     */
-    protected $beforeCellAddress;
-
-    /**
-     * @var int
-     */
-    protected $beforeColumn;
-
-    /**
-     * @var int
-     */
-    protected $beforeRow;
-
-    /**
-     * @var int
-     */
-    protected $numberOfColumns;
-
-    /**
-     * @var int
-     */
-    protected $numberOfRows;
+    protected string $beforeCellAddress;
+
+    protected int $beforeColumn;
+
+    protected int $beforeRow;
+
+    protected int $numberOfColumns;
+
+    protected int $numberOfRows;
 
     public function __construct(string $beforeCellAddress = 'A1', int $numberOfColumns = 0, int $numberOfRows = 0)
     {
@@ -40,7 +25,7 @@ public function __construct(string $beforeCellAddress = 'A1', int $numberOfColum
 
         // Get coordinate of $beforeCellAddress
         [$beforeColumn, $beforeRow] = Coordinate::coordinateFromString($beforeCellAddress);
-        $this->beforeColumn = (int) Coordinate::columnIndexFromString($beforeColumn);
+        $this->beforeColumn = Coordinate::columnIndexFromString($beforeColumn);
         $this->beforeRow = (int) $beforeRow;
     }
 
@@ -64,7 +49,7 @@ public function updateCellReference(string $cellReference = 'A1', bool $includeA
 
         // Get coordinate of $cellReference
         [$newColumn, $newRow] = Coordinate::coordinateFromString($cellReference);
-        $newColumnIndex = (int) Coordinate::columnIndexFromString(str_replace('$', '', $newColumn));
+        $newColumnIndex = Coordinate::columnIndexFromString(str_replace('$', '', $newColumn));
         $newRowIndex = (int) str_replace('$', '', $newRow);
 
         $absoluteColumn = $newColumn[0] === '$' ? '$' : '';
diff --git a/src/PhpSpreadsheet/Chart/Axis.php b/src/PhpSpreadsheet/Chart/Axis.php
index 3d48134684..dd77dac967 100644
--- a/src/PhpSpreadsheet/Chart/Axis.php
+++ b/src/PhpSpreadsheet/Chart/Axis.php
@@ -26,17 +26,13 @@ public function __construct()
 
     /**
      * Chart Major Gridlines as.
-     *
-     * @var ?GridLines
      */
-    private $majorGridlines;
+    private ?GridLines $majorGridlines = null;
 
     /**
      * Chart Minor Gridlines as.
-     *
-     * @var ?GridLines
      */
-    private $minorGridlines;
+    private ?GridLines $minorGridlines = null;
 
     /**
      * Axis Number.
@@ -49,11 +45,9 @@ public function __construct()
         'numeric' => null,
     ];
 
-    /** @var string */
-    private $axisType = '';
+    private string $axisType = '';
 
-    /** @var ?AxisText */
-    private $axisText;
+    private ?AxisText $axisText = null;
 
     /**
      * Axis Options.
@@ -80,10 +74,8 @@ public function __construct()
 
     /**
      * Fill Properties.
-     *
-     * @var ChartColor
      */
-    private $fillColor;
+    private ChartColor $fillColor;
 
     private const NUMERIC_FORMAT = [
         Properties::FORMAT_CODE_NUMBER,
@@ -123,10 +115,8 @@ public function getAxisNumberFormat()
 
     /**
      * Get Axis Number Source Linked.
-     *
-     * @return string
      */
-    public function getAxisNumberSourceLinked()
+    public function getAxisNumberSourceLinked(): string
     {
         return (string) $this->axisNumber['source_linked'];
     }
@@ -233,7 +223,7 @@ public function setAxisType(string $type): self
      * @param ?int $alpha
      * @param ?string $AlphaType
      */
-    public function setFillParameters($color, $alpha = null, $AlphaType = ChartColor::EXCEL_COLOR_TYPE_RGB): void
+    public function setFillParameters(?string $color, $alpha = null, ?string $AlphaType = ChartColor::EXCEL_COLOR_TYPE_RGB): void
     {
         $this->fillColor->setColorProperties($color, $alpha, $AlphaType);
     }
@@ -242,10 +232,8 @@ public function setFillParameters($color, $alpha = null, $AlphaType = ChartColor
      * Get Fill Property.
      *
      * @param string $property
-     *
-     * @return string
      */
-    public function getFillProperty($property)
+    public function getFillProperty($property): string
     {
         return (string) $this->fillColor->getColorProperty($property);
     }
@@ -271,8 +259,7 @@ public function getLineProperty($propertyName)
         return $this->getLineColorProperty($propertyName);
     }
 
-    /** @var string */
-    private $crossBetween = ''; // 'between' or 'midCat' might be better
+    private string $crossBetween = ''; // 'between' or 'midCat' might be better
 
     public function setCrossBetween(string $crossBetween): self
     {
diff --git a/src/PhpSpreadsheet/Chart/AxisText.php b/src/PhpSpreadsheet/Chart/AxisText.php
index cd9ba2ce29..e06a2c88a8 100644
--- a/src/PhpSpreadsheet/Chart/AxisText.php
+++ b/src/PhpSpreadsheet/Chart/AxisText.php
@@ -6,11 +6,9 @@
 
 class AxisText extends Properties
 {
-    /** @var ?int */
-    private $rotation;
+    private ?int $rotation = null;
 
-    /** @var Font */
-    private $font;
+    private Font $font;
 
     public function __construct()
     {
diff --git a/src/PhpSpreadsheet/Chart/Chart.php b/src/PhpSpreadsheet/Chart/Chart.php
index 38c69a4636..1cb6d6fe20 100644
--- a/src/PhpSpreadsheet/Chart/Chart.php
+++ b/src/PhpSpreadsheet/Chart/Chart.php
@@ -16,45 +16,33 @@ class Chart
 
     /**
      * Worksheet.
-     *
-     * @var ?Worksheet
      */
-    private $worksheet;
+    private ?Worksheet $worksheet = null;
 
     /**
      * Chart Title.
-     *
-     * @var ?Title
      */
-    private $title;
+    private ?Title $title;
 
     /**
      * Chart Legend.
-     *
-     * @var ?Legend
      */
-    private $legend;
+    private ?Legend $legend;
 
     /**
      * X-Axis Label.
-     *
-     * @var ?Title
      */
-    private $xAxisLabel;
+    private ?Title $xAxisLabel;
 
     /**
      * Y-Axis Label.
-     *
-     * @var ?Title
      */
-    private $yAxisLabel;
+    private ?Title $yAxisLabel;
 
     /**
      * Chart Plot Area.
-     *
-     * @var ?PlotArea
      */
-    private $plotArea;
+    private ?PlotArea $plotArea;
 
     /**
      * Plot Visible Only.
@@ -72,17 +60,13 @@ class Chart
 
     /**
      * Chart Asix Y as.
-     *
-     * @var Axis
      */
-    private $yAxis;
+    private Axis $yAxis;
 
     /**
      * Chart Asix X as.
-     *
-     * @var Axis
      */
-    private $xAxis;
+    private Axis $xAxis;
 
     /**
      * Top-Left Cell Position.
@@ -107,10 +91,8 @@ class Chart
 
     /**
      * Bottom-Right Cell Position.
-     *
-     * @var string
      */
-    private $bottomRightCellRef = '';
+    private string $bottomRightCellRef = '';
 
     /**
      * Bottom-Right X-Offset.
@@ -126,17 +108,13 @@ class Chart
      */
     private $bottomRightYOffset = 10;
 
-    /** @var ?int */
-    private $rotX;
+    private ?int $rotX = null;
 
-    /** @var ?int */
-    private $rotY;
+    private ?int $rotY = null;
 
-    /** @var ?int */
-    private $rAngAx;
+    private ?int $rAngAx = null;
 
-    /** @var ?int */
-    private $perspective;
+    private ?int $perspective = null;
 
     /** @var bool */
     private $oneCellAnchor = false;
@@ -150,11 +128,9 @@ class Chart
     /** @var bool */
     private $roundedCorners = false;
 
-    /** @var GridLines */
-    private $borderLines;
+    private GridLines $borderLines;
 
-    /** @var ChartColor */
-    private $fillColor;
+    private ChartColor $fillColor;
 
     /**
      * Create a new Chart.
@@ -216,7 +192,7 @@ public function getWorksheet(): ?Worksheet
      *
      * @return $this
      */
-    public function setWorksheet(?Worksheet $worksheet = null)
+    public function setWorksheet(?Worksheet $worksheet = null): static
     {
         $this->worksheet = $worksheet;
 
@@ -233,7 +209,7 @@ public function getTitle(): ?Title
      *
      * @return $this
      */
-    public function setTitle(Title $title)
+    public function setTitle(Title $title): static
     {
         $this->title = $title;
 
@@ -250,7 +226,7 @@ public function getLegend(): ?Legend
      *
      * @return $this
      */
-    public function setLegend(Legend $legend)
+    public function setLegend(Legend $legend): static
     {
         $this->legend = $legend;
 
@@ -267,7 +243,7 @@ public function getXAxisLabel(): ?Title
      *
      * @return $this
      */
-    public function setXAxisLabel(Title $label)
+    public function setXAxisLabel(Title $label): static
     {
         $this->xAxisLabel = $label;
 
@@ -284,7 +260,7 @@ public function getYAxisLabel(): ?Title
      *
      * @return $this
      */
-    public function setYAxisLabel(Title $label)
+    public function setYAxisLabel(Title $label): static
     {
         $this->yAxisLabel = $label;
 
@@ -323,7 +299,7 @@ public function getPlotVisibleOnly()
      *
      * @return $this
      */
-    public function setPlotVisibleOnly($plotVisibleOnly)
+    public function setPlotVisibleOnly($plotVisibleOnly): static
     {
         $this->plotVisibleOnly = $plotVisibleOnly;
 
@@ -347,7 +323,7 @@ public function getDisplayBlanksAs()
      *
      * @return $this
      */
-    public function setDisplayBlanksAs($displayBlanksAs)
+    public function setDisplayBlanksAs($displayBlanksAs): static
     {
         $this->displayBlanksAs = $displayBlanksAs;
 
@@ -419,7 +395,7 @@ public function getMinorGridlines(): ?GridLines
      *
      * @return $this
      */
-    public function setTopLeftPosition($cellAddress, $xOffset = null, $yOffset = null)
+    public function setTopLeftPosition($cellAddress, $xOffset = null, $yOffset = null): static
     {
         $this->topLeftCellRef = $cellAddress;
         if ($xOffset !== null) {
@@ -465,7 +441,7 @@ public function getTopLeftCell()
      *
      * @return $this
      */
-    public function setTopLeftCell($cellAddress)
+    public function setTopLeftCell($cellAddress): static
     {
         $this->topLeftCellRef = $cellAddress;
 
@@ -480,7 +456,7 @@ public function setTopLeftCell($cellAddress)
      *
      * @return $this
      */
-    public function setTopLeftOffset($xOffset, $yOffset)
+    public function setTopLeftOffset($xOffset, $yOffset): static
     {
         if ($xOffset !== null) {
             $this->setTopLeftXOffset($xOffset);
@@ -498,7 +474,7 @@ public function setTopLeftOffset($xOffset, $yOffset)
      *
      * @return int[]
      */
-    public function getTopLeftOffset()
+    public function getTopLeftOffset(): array
     {
         return [
             'X' => $this->topLeftXOffset,
@@ -511,7 +487,7 @@ public function getTopLeftOffset()
      *
      * @return $this
      */
-    public function setTopLeftXOffset($xOffset)
+    public function setTopLeftXOffset($xOffset): static
     {
         $this->topLeftXOffset = $xOffset;
 
@@ -528,7 +504,7 @@ public function getTopLeftXOffset(): int
      *
      * @return $this
      */
-    public function setTopLeftYOffset($yOffset)
+    public function setTopLeftYOffset($yOffset): static
     {
         $this->topLeftYOffset = $yOffset;
 
@@ -549,7 +525,7 @@ public function getTopLeftYOffset(): int
      *
      * @return $this
      */
-    public function setBottomRightPosition($cellAddress = '', $xOffset = null, $yOffset = null)
+    public function setBottomRightPosition($cellAddress = '', $xOffset = null, $yOffset = null): static
     {
         $this->bottomRightCellRef = $cellAddress;
         if ($xOffset !== null) {
@@ -567,7 +543,7 @@ public function setBottomRightPosition($cellAddress = '', $xOffset = null, $yOff
      *
      * @return array an associative array containing the cell address, X-Offset and Y-Offset from the top left of that cell
      */
-    public function getBottomRightPosition()
+    public function getBottomRightPosition(): array
     {
         return [
             'cell' => $this->bottomRightCellRef,
@@ -581,7 +557,7 @@ public function getBottomRightPosition()
      *
      * @return $this
      */
-    public function setBottomRightCell(string $cellAddress = '')
+    public function setBottomRightCell(string $cellAddress = ''): static
     {
         $this->bottomRightCellRef = $cellAddress;
 
@@ -604,7 +580,7 @@ public function getBottomRightCell(): string
      *
      * @return $this
      */
-    public function setBottomRightOffset($xOffset, $yOffset)
+    public function setBottomRightOffset($xOffset, $yOffset): static
     {
         if ($xOffset !== null) {
             $this->setBottomRightXOffset($xOffset);
@@ -622,7 +598,7 @@ public function setBottomRightOffset($xOffset, $yOffset)
      *
      * @return int[]
      */
-    public function getBottomRightOffset()
+    public function getBottomRightOffset(): array
     {
         return [
             'X' => $this->bottomRightXOffset,
@@ -635,7 +611,7 @@ public function getBottomRightOffset()
      *
      * @return $this
      */
-    public function setBottomRightXOffset($xOffset)
+    public function setBottomRightXOffset($xOffset): static
     {
         $this->bottomRightXOffset = $xOffset;
 
@@ -652,7 +628,7 @@ public function getBottomRightXOffset(): int
      *
      * @return $this
      */
-    public function setBottomRightYOffset($yOffset)
+    public function setBottomRightYOffset($yOffset): static
     {
         $this->bottomRightYOffset = $yOffset;
 
diff --git a/src/PhpSpreadsheet/Chart/ChartColor.php b/src/PhpSpreadsheet/Chart/ChartColor.php
index 87f3102009..df08adb5d2 100644
--- a/src/PhpSpreadsheet/Chart/ChartColor.php
+++ b/src/PhpSpreadsheet/Chart/ChartColor.php
@@ -15,17 +15,13 @@ class ChartColor
         self::EXCEL_COLOR_TYPE_STANDARD,
     ];
 
-    /** @var string */
-    private $value = '';
+    private string $value = '';
 
-    /** @var string */
-    private $type = '';
+    private string $type = '';
 
-    /** @var ?int */
-    private $alpha;
+    private ?int $alpha = null;
 
-    /** @var ?int */
-    private $brightness;
+    private ?int $brightness = null;
 
     /**
      * @param string|string[] $value
diff --git a/src/PhpSpreadsheet/Chart/DataSeries.php b/src/PhpSpreadsheet/Chart/DataSeries.php
index 5d33e96d09..a290eff2f0 100644
--- a/src/PhpSpreadsheet/Chart/DataSeries.php
+++ b/src/PhpSpreadsheet/Chart/DataSeries.php
@@ -77,21 +77,21 @@ class DataSeries
      *
      * @var int[]
      */
-    private $plotOrder = [];
+    private array $plotOrder;
 
     /**
      * Plot Label.
      *
      * @var DataSeriesValues[]
      */
-    private $plotLabel = [];
+    private array $plotLabel;
 
     /**
      * Plot Category.
      *
      * @var DataSeriesValues[]
      */
-    private $plotCategory = [];
+    private array $plotCategory;
 
     /**
      * Smooth Line. Must be specified for both DataSeries and DataSeriesValues.
@@ -105,7 +105,7 @@ class DataSeries
      *
      * @var DataSeriesValues[]
      */
-    private $plotValues = [];
+    private array $plotValues;
 
     /**
      * Plot Bubble Sizes.
@@ -170,7 +170,7 @@ public function getPlotType()
      *
      * @return $this
      */
-    public function setPlotType($plotType)
+    public function setPlotType($plotType): static
     {
         $this->plotType = $plotType;
 
@@ -194,7 +194,7 @@ public function getPlotGrouping()
      *
      * @return $this
      */
-    public function setPlotGrouping($groupingType)
+    public function setPlotGrouping($groupingType): static
     {
         $this->plotGrouping = $groupingType;
 
@@ -218,7 +218,7 @@ public function getPlotDirection()
      *
      * @return $this
      */
-    public function setPlotDirection($plotDirection)
+    public function setPlotDirection($plotDirection): static
     {
         $this->plotDirection = $plotDirection;
 
@@ -308,7 +308,7 @@ public function getPlotStyle()
      *
      * @return $this
      */
-    public function setPlotStyle($plotStyle)
+    public function setPlotStyle($plotStyle): static
     {
         $this->plotStyle = $plotStyle;
 
@@ -366,10 +366,8 @@ public function setPlotBubbleSizes(array $plotBubbleSizes): self
 
     /**
      * Get Number of Plot Series.
-     *
-     * @return int
      */
-    public function getPlotSeriesCount()
+    public function getPlotSeriesCount(): int
     {
         return count($this->plotValues);
     }
@@ -391,7 +389,7 @@ public function getSmoothLine()
      *
      * @return $this
      */
-    public function setSmoothLine($smoothLine)
+    public function setSmoothLine($smoothLine): static
     {
         $this->smoothLine = $smoothLine;
 
diff --git a/src/PhpSpreadsheet/Chart/DataSeriesValues.php b/src/PhpSpreadsheet/Chart/DataSeriesValues.php
index c86f5569b3..1a939bbd72 100644
--- a/src/PhpSpreadsheet/Chart/DataSeriesValues.php
+++ b/src/PhpSpreadsheet/Chart/DataSeriesValues.php
@@ -45,11 +45,9 @@ class DataSeriesValues extends Properties
      */
     private $pointMarker;
 
-    /** @var ChartColor */
-    private $markerFillColor;
+    private ChartColor $markerFillColor;
 
-    /** @var ChartColor */
-    private $markerBorderColor;
+    private ChartColor $markerBorderColor;
 
     /**
      * Series Point Size.
@@ -85,8 +83,7 @@ class DataSeriesValues extends Properties
     /** @var bool */
     private $bubble3D = false;
 
-    /** @var ?Layout */
-    private $labelLayout;
+    private ?Layout $labelLayout = null;
 
     /** @var TrendLine[] */
     private $trendLines = [];
@@ -144,7 +141,7 @@ public function getDataType()
      *
      * @return $this
      */
-    public function setDataType($dataType)
+    public function setDataType($dataType): static
     {
         if (!in_array($dataType, self::DATA_TYPE_VALUES)) {
             throw new Exception('Invalid datatype for chart data series values');
@@ -171,7 +168,7 @@ public function getDataSource()
      *
      * @return $this
      */
-    public function setDataSource($dataSource)
+    public function setDataSource($dataSource): static
     {
         $this->dataSource = $dataSource;
 
@@ -195,7 +192,7 @@ public function getPointMarker()
      *
      * @return $this
      */
-    public function setPointMarker($marker)
+    public function setPointMarker($marker): static
     {
         $this->pointMarker = $marker;
 
@@ -225,7 +222,7 @@ public function getPointSize(): int
      *
      * @return $this
      */
-    public function setPointSize(int $size = 3)
+    public function setPointSize(int $size = 3): static
     {
         $this->pointSize = $size;
 
@@ -249,7 +246,7 @@ public function getFormatCode()
      *
      * @return $this
      */
-    public function setFormatCode($formatCode)
+    public function setFormatCode($formatCode): static
     {
         $this->formatCode = $formatCode;
 
@@ -316,7 +313,7 @@ private function chartColorToString(ChartColor $chartColor): string
      *
      * @return string|string[] HEX color or array with HEX colors
      */
-    public function getFillColor()
+    public function getFillColor(): string|array
     {
         if ($this->fillColor === null) {
             return '';
@@ -338,9 +335,9 @@ public function getFillColor()
      *
      * @param ChartColor|ChartColor[]|string|string[] $color HEX color or array with HEX colors
      *
-     * @return   DataSeriesValues
+     * @return   $this
      */
-    public function setFillColor($color)
+    public function setFillColor($color): static
     {
         if (is_array($color)) {
             $this->fillColor = [];
@@ -367,7 +364,7 @@ public function setFillColor($color)
      *
      * @return bool true if validation was successful
      */
-    private function validateColor($color)
+    private function validateColor(string $color): bool
     {
         if (!preg_match('/^[a-f0-9]{6}$/i', $color)) {
             throw new Exception(sprintf('Invalid hex color for chart series (color: "%s")', $color));
@@ -393,7 +390,7 @@ public function getLineWidth()
      *
      * @return $this
      */
-    public function setLineWidth($width)
+    public function setLineWidth($width): static
     {
         $this->lineStyleProperties['width'] = $width;
 
@@ -402,10 +399,8 @@ public function setLineWidth($width)
 
     /**
      * Identify if the Data Series is a multi-level or a simple series.
-     *
-     * @return null|bool
      */
-    public function isMultiLevelSeries()
+    public function isMultiLevelSeries(): ?bool
     {
         if (!empty($this->dataValues)) {
             return is_array(array_values($this->dataValues)[0]);
@@ -463,7 +458,7 @@ public function getDataValue()
      *
      * @return $this
      */
-    public function setDataValues($dataValues)
+    public function setDataValues($dataValues): static
     {
         $this->dataValues = Functions::flattenArray($dataValues);
         $this->pointCount = count($dataValues);
@@ -492,7 +487,7 @@ public function refresh(Worksheet $worksheet, bool $flatten = true): void
                 unset($dataValue);
             } else {
                 [$worksheet, $cellRange] = Worksheet::extractSheetTitle($this->dataSource, true);
-                $dimensions = Coordinate::rangeDimension(str_replace('$', '', $cellRange));
+                $dimensions = Coordinate::rangeDimension(str_replace('$', '', $cellRange ?? ''));
                 if (($dimensions[0] == 1) || ($dimensions[1] == 1)) {
                     $this->dataValues = Functions::flattenArray($newDataValues);
                 } else {
@@ -562,7 +557,7 @@ public function getSmoothLine()
      *
      * @return $this
      */
-    public function setSmoothLine($smoothLine)
+    public function setSmoothLine($smoothLine): static
     {
         $this->smoothLine = $smoothLine;
 
diff --git a/src/PhpSpreadsheet/Chart/Layout.php b/src/PhpSpreadsheet/Chart/Layout.php
index ac36c25c9f..e9830b30c3 100644
--- a/src/PhpSpreadsheet/Chart/Layout.php
+++ b/src/PhpSpreadsheet/Chart/Layout.php
@@ -8,132 +8,96 @@ class Layout
 {
     /**
      * layoutTarget.
-     *
-     * @var ?string
      */
-    private $layoutTarget;
+    private ?string $layoutTarget = null;
 
     /**
      * X Mode.
-     *
-     * @var ?string
      */
-    private $xMode;
+    private ?string $xMode = null;
 
     /**
      * Y Mode.
-     *
-     * @var ?string
      */
-    private $yMode;
+    private ?string $yMode = null;
 
     /**
      * X-Position.
-     *
-     * @var ?float
      */
-    private $xPos;
+    private ?float $xPos = null;
 
     /**
      * Y-Position.
-     *
-     * @var ?float
      */
-    private $yPos;
+    private ?float $yPos = null;
 
     /**
      * width.
-     *
-     * @var ?float
      */
-    private $width;
+    private ?float $width = null;
 
     /**
      * height.
-     *
-     * @var ?float
      */
-    private $height;
+    private ?float $height = null;
 
     /**
      * Position - t=top.
-     *
-     * @var string
      */
-    private $dLblPos = '';
+    private string $dLblPos = '';
 
-    /** @var string */
-    private $numFmtCode = '';
+    private string $numFmtCode = '';
 
-    /** @var bool */
-    private $numFmtLinked = false;
+    private bool $numFmtLinked = false;
 
     /**
      * show legend key
      * Specifies that legend keys should be shown in data labels.
-     *
-     * @var ?bool
      */
-    private $showLegendKey;
+    private ?bool $showLegendKey = null;
 
     /**
      * show value
      * Specifies that the value should be shown in a data label.
-     *
-     * @var ?bool
      */
-    private $showVal;
+    private ?bool $showVal = null;
 
     /**
      * show category name
      * Specifies that the category name should be shown in the data label.
-     *
-     * @var ?bool
      */
-    private $showCatName;
+    private ?bool $showCatName = null;
 
     /**
      * show data series name
      * Specifies that the series name should be shown in the data label.
-     *
-     * @var ?bool
      */
-    private $showSerName;
+    private ?bool $showSerName = null;
 
     /**
      * show percentage
      * Specifies that the percentage should be shown in the data label.
-     *
-     * @var ?bool
      */
-    private $showPercent;
+    private ?bool $showPercent = null;
 
     /**
      * show bubble size.
-     *
-     * @var ?bool
      */
-    private $showBubbleSize;
+    private ?bool $showBubbleSize = null;
 
     /**
      * show leader lines
      * Specifies that leader lines should be shown for the data label.
-     *
-     * @var ?bool
      */
-    private $showLeaderLines;
+    private ?bool $showLeaderLines = null;
 
-    /** @var ?ChartColor */
-    private $labelFillColor;
+    private ?ChartColor $labelFillColor = null;
 
-    /** @var ?ChartColor */
-    private $labelBorderColor;
+    private ?ChartColor $labelBorderColor = null;
 
-    /** @var ?Font */
-    private $labelFont;
+    private ?Font $labelFont = null;
 
-    /** @var Properties */
-    private $labelEffects;
+    private ?Properties $labelEffects = null;
 
     /**
      * Create a new Layout.
@@ -222,7 +186,7 @@ public function getLayoutTarget()
      *
      * @return $this
      */
-    public function setLayoutTarget($target)
+    public function setLayoutTarget(?string $target): static
     {
         $this->layoutTarget = $target;
 
@@ -246,7 +210,7 @@ public function getXMode()
      *
      * @return $this
      */
-    public function setXMode($mode)
+    public function setXMode($mode): static
     {
         $this->xMode = (string) $mode;
 
@@ -270,7 +234,7 @@ public function getYMode()
      *
      * @return $this
      */
-    public function setYMode($mode)
+    public function setYMode($mode): static
     {
         $this->yMode = (string) $mode;
 
@@ -290,13 +254,11 @@ public function getXPosition()
     /**
      * Set X-Position.
      *
-     * @param ?float $position
-     *
      * @return $this
      */
-    public function setXPosition($position)
+    public function setXPosition(float $position): static
     {
-        $this->xPos = (float) $position;
+        $this->xPos = $position;
 
         return $this;
     }
@@ -314,13 +276,11 @@ public function getYPosition()
     /**
      * Set Y-Position.
      *
-     * @param ?float $position
-     *
      * @return $this
      */
-    public function setYPosition($position)
+    public function setYPosition(float $position): static
     {
-        $this->yPos = (float) $position;
+        $this->yPos = $position;
 
         return $this;
     }
@@ -342,7 +302,7 @@ public function getWidth()
      *
      * @return $this
      */
-    public function setWidth($width)
+    public function setWidth(?float $width): static
     {
         $this->width = $width;
 
@@ -362,11 +322,9 @@ public function getHeight()
     /**
      * Set Height.
      *
-     * @param ?float $height
-     *
      * @return $this
      */
-    public function setHeight($height)
+    public function setHeight(?float $height): static
     {
         $this->height = $height;
 
diff --git a/src/PhpSpreadsheet/Chart/Legend.php b/src/PhpSpreadsheet/Chart/Legend.php
index 04040aed6a..69ee8aa17f 100644
--- a/src/PhpSpreadsheet/Chart/Legend.php
+++ b/src/PhpSpreadsheet/Chart/Legend.php
@@ -43,19 +43,14 @@ class Legend
 
     /**
      * Legend Layout.
-     *
-     * @var ?Layout
      */
-    private $layout;
+    private ?Layout $layout;
 
-    /** @var GridLines */
-    private $borderLines;
+    private GridLines $borderLines;
 
-    /** @var ChartColor */
-    private $fillColor;
+    private ChartColor $fillColor;
 
-    /** @var ?AxisText */
-    private $legendText;
+    private ?AxisText $legendText = null;
 
     /**
      * Create a new Legend.
@@ -92,10 +87,8 @@ public function getPosition()
      * Get legend position using an excel string value.
      *
      * @param string $position see self::POSITION_*
-     *
-     * @return bool
      */
-    public function setPosition($position)
+    public function setPosition($position): bool
     {
         if (!in_array($position, self::POSITION_XLREF)) {
             return false;
@@ -108,10 +101,8 @@ public function setPosition($position)
 
     /**
      * Get legend position as an Excel internal numeric value.
-     *
-     * @return false|int
      */
-    public function getPositionXL()
+    public function getPositionXL(): false|int
     {
         // Scrutinizer thinks the following could return string. It is wrong.
         return array_search($this->position, self::POSITION_XLREF);
@@ -121,10 +112,8 @@ public function getPositionXL()
      * Set legend position using an Excel internal numeric value.
      *
      * @param int $positionXL see self::XL_LEGEND_POSITION_*
-     *
-     * @return bool
      */
-    public function setPositionXL($positionXL)
+    public function setPositionXL($positionXL): bool
     {
         if (!isset(self::POSITION_XLREF[$positionXL])) {
             return false;
diff --git a/src/PhpSpreadsheet/Chart/PlotArea.php b/src/PhpSpreadsheet/Chart/PlotArea.php
index 2b78d9a4eb..89a2be7780 100644
--- a/src/PhpSpreadsheet/Chart/PlotArea.php
+++ b/src/PhpSpreadsheet/Chart/PlotArea.php
@@ -25,24 +25,20 @@ class PlotArea
 
     /**
      * PlotArea Gradient Angle.
-     *
-     * @var ?float
      */
-    private $gradientFillAngle;
+    private ?float $gradientFillAngle = null;
 
     /**
      * PlotArea Layout.
-     *
-     * @var ?Layout
      */
-    private $layout;
+    private ?Layout $layout;
 
     /**
      * Plot Series.
      *
      * @var DataSeries[]
      */
-    private $plotSeries = [];
+    private array $plotSeries;
 
     /**
      * Create a new PlotArea.
@@ -73,7 +69,7 @@ public function getPlotGroupCount(): int
      *
      * @return int
      */
-    public function getPlotSeriesCount()
+    public function getPlotSeriesCount(): int|float
     {
         $seriesCount = 0;
         foreach ($this->plotSeries as $plot) {
@@ -112,7 +108,7 @@ public function getPlotGroupByIndex($index)
      *
      * @return $this
      */
-    public function setPlotSeries(array $plotSeries)
+    public function setPlotSeries(array $plotSeries): static
     {
         $this->plotSeries = $plotSeries;
 
@@ -164,8 +160,7 @@ public function getGradientFillStops()
         return $this->gradientFillStops;
     }
 
-    /** @var ?int */
-    private $gapWidth;
+    private ?int $gapWidth = null;
 
     /** @var bool */
     private $useUpBars = false;
diff --git a/src/PhpSpreadsheet/Chart/Properties.php b/src/PhpSpreadsheet/Chart/Properties.php
index edb775456f..36b6eb76fd 100644
--- a/src/PhpSpreadsheet/Chart/Properties.php
+++ b/src/PhpSpreadsheet/Chart/Properties.php
@@ -125,8 +125,7 @@ abstract class Properties
     /** @var ?float */
     protected $glowSize;
 
-    /** @var ChartColor */
-    protected $glowColor;
+    protected ChartColor $glowColor;
 
     /** @var array */
     protected $softEdges = [
@@ -136,8 +135,7 @@ abstract class Properties
     /** @var array */
     protected $shadowProperties = self::PRESETS_OPTIONS[0];
 
-    /** @var ChartColor */
-    protected $shadowColor;
+    protected ChartColor $shadowColor;
 
     public function __construct()
     {
@@ -611,11 +609,9 @@ public function setShadowProperties($presets, $colorValue = null, $colorType = n
     /**
      * Set Shadow Presets Properties.
      *
-     * @param int $presets
-     *
      * @return $this
      */
-    protected function setShadowPresetsProperties($presets)
+    protected function setShadowPresetsProperties(int $presets)
     {
         $this->shadowProperties['presets'] = $presets;
         $this->setShadowPropertiesMapValues($this->getShadowPresetsMap($presets));
@@ -628,11 +624,9 @@ protected function setShadowPresetsProperties($presets)
     /**
      * Set Shadow Properties Values.
      *
-     * @param mixed $reference
-     *
      * @return $this
      */
-    protected function setShadowPropertiesMapValues(array $propertiesMap, &$reference = null)
+    protected function setShadowPropertiesMapValues(array $propertiesMap, ?array &$reference = null)
     {
         $base_reference = $reference;
         foreach ($propertiesMap as $property_key => $property_val) {
@@ -736,8 +730,7 @@ public function getShadowArray(): array
         return $array;
     }
 
-    /** @var ChartColor */
-    protected $lineColor;
+    protected ChartColor $lineColor;
 
     /** @var array */
     protected $lineStyleProperties = [
@@ -780,11 +773,10 @@ public function getLineColor(): ChartColor
     /**
      * Set Line Color Properties.
      *
-     * @param string $value
      * @param ?int $alpha
      * @param ?string $colorType
      */
-    public function setLineColorProperties($value, $alpha = null, $colorType = null): void
+    public function setLineColorProperties(?string $value, $alpha = null, ?string $colorType = null): void
     {
         $this->activateObject();
         $this->lineColor->setColorPropertiesArray(
diff --git a/src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php b/src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php
index d676f1d33b..40ce338d93 100644
--- a/src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php
+++ b/src/PhpSpreadsheet/Chart/Renderer/JpGraphRendererBase.php
@@ -38,9 +38,9 @@ abstract class JpGraphRendererBase implements IRenderer
         'goldenrod2',
     ];
 
-    private static $markSet;
+    private static array $markSet;
 
-    private $chart;
+    private Chart $chart;
 
     private $graph;
 
@@ -102,7 +102,7 @@ private function formatPointMarker($seriesPlot, $markerID)
         return $seriesPlot;
     }
 
-    private function formatDataSetLabels($groupID, $datasetLabels, $rotation = '')
+    private function formatDataSetLabels(int $groupID, array $datasetLabels, $rotation = '')
     {
         $datasetLabelFormatCode = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotCategoryByIndex(0)->getFormatCode() ?? '';
         //    Retrieve any label formatting code
@@ -129,7 +129,7 @@ private function formatDataSetLabels($groupID, $datasetLabels, $rotation = '')
         return $datasetLabels;
     }
 
-    private function percentageSumCalculation($groupID, $seriesCount)
+    private function percentageSumCalculation(int $groupID, $seriesCount)
     {
         $sumValues = [];
         //    Adjust our values to a percentage value across all series in the group
@@ -151,7 +151,7 @@ private function percentageSumCalculation($groupID, $seriesCount)
         return $sumValues;
     }
 
-    private function percentageAdjustValues($dataValues, $sumValues)
+    private function percentageAdjustValues(array $dataValues, array $sumValues)
     {
         foreach ($dataValues as $k => $dataValue) {
             $dataValues[$k] = $dataValue / $sumValues[$k] * 100;
@@ -219,7 +219,7 @@ private function renderLegend(): void
         }
     }
 
-    private function renderCartesianPlotArea($type = 'textlin'): void
+    private function renderCartesianPlotArea(string $type = 'textlin'): void
     {
         $this->graph = new Graph(self::$width, self::$height);
         $this->graph->SetScale($type);
@@ -271,7 +271,7 @@ private function renderRadarPlotArea(): void
         $this->renderTitle();
     }
 
-    private function renderPlotLine($groupID, $filled = false, $combination = false): void
+    private function renderPlotLine(int $groupID, bool $filled = false, bool $combination = false): void
     {
         $grouping = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotGrouping();
 
@@ -338,7 +338,7 @@ private function renderPlotLine($groupID, $filled = false, $combination = false)
         $this->graph->Add($groupPlot);
     }
 
-    private function renderPlotBar($groupID, $dimensions = '2d'): void
+    private function renderPlotBar(int $groupID, ?string $dimensions = '2d'): void
     {
         $rotation = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotDirection();
         //    Rotate for bar rather than column chart
@@ -426,7 +426,7 @@ private function renderPlotBar($groupID, $dimensions = '2d'): void
         $this->graph->Add($groupPlot);
     }
 
-    private function renderPlotScatter($groupID, $bubble): void
+    private function renderPlotScatter(int $groupID, bool $bubble): void
     {
         $scatterStyle = $bubbleSize = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotStyle();
 
@@ -490,7 +490,7 @@ private function renderPlotScatter($groupID, $bubble): void
         }
     }
 
-    private function renderPlotRadar($groupID): void
+    private function renderPlotRadar(int $groupID): void
     {
         $radarStyle = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotStyle();
 
@@ -527,7 +527,7 @@ private function renderPlotRadar($groupID): void
         }
     }
 
-    private function renderPlotContour($groupID): void
+    private function renderPlotContour(int $groupID): void
     {
         $seriesCount = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotSeriesCount();
 
@@ -543,7 +543,7 @@ private function renderPlotContour($groupID): void
         $this->graph->Add($seriesPlot);
     }
 
-    private function renderPlotStock($groupID): void
+    private function renderPlotStock(int $groupID): void
     {
         $seriesCount = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotSeriesCount();
         $plotOrder = $this->chart->getPlotArea()->getPlotGroupByIndex($groupID)->getPlotOrder();
@@ -605,7 +605,7 @@ private function renderLineChart($groupCount): void
         }
     }
 
-    private function renderBarChart($groupCount, $dimensions = '2d'): void
+    private function renderBarChart($groupCount, ?string $dimensions = '2d'): void
     {
         $this->renderCartesianPlotArea();
 
@@ -632,7 +632,7 @@ private function renderBubbleChart($groupCount): void
         }
     }
 
-    private function renderPieChart($groupCount, $dimensions = '2d', $doughnut = false, $multiplePlots = false): void
+    private function renderPieChart($groupCount, ?string $dimensions = '2d', bool $doughnut = false, bool $multiplePlots = false): void
     {
         $this->renderPiePlotArea();
 
@@ -729,7 +729,7 @@ private function renderContourChart($groupCount): void
         }
     }
 
-    private function renderCombinationChart($groupCount, $outputDestination)
+    private function renderCombinationChart($groupCount, $outputDestination): bool
     {
         $this->renderCartesianPlotArea();
 
diff --git a/src/PhpSpreadsheet/Chart/Renderer/MtJpGraphRenderer.php b/src/PhpSpreadsheet/Chart/Renderer/MtJpGraphRenderer.php
index b5e70d3a19..9697920328 100644
--- a/src/PhpSpreadsheet/Chart/Renderer/MtJpGraphRenderer.php
+++ b/src/PhpSpreadsheet/Chart/Renderer/MtJpGraphRenderer.php
@@ -2,6 +2,8 @@
 
 namespace PhpOffice\PhpSpreadsheet\Chart\Renderer;
 
+use mitoteam\jpgraph\MtJpGraph;
+
 /**
  * Jpgraph is not officially maintained by Composer at packagist.org.
  *
@@ -19,7 +21,7 @@ protected static function init(): void
             return;
         }
 
-        \mitoteam\jpgraph\MtJpGraph::load([
+        MtJpGraph::load([
             'bar',
             'contour',
             'line',
diff --git a/src/PhpSpreadsheet/Chart/Title.php b/src/PhpSpreadsheet/Chart/Title.php
index 9c99ccac19..787b96bcd4 100644
--- a/src/PhpSpreadsheet/Chart/Title.php
+++ b/src/PhpSpreadsheet/Chart/Title.php
@@ -22,10 +22,8 @@ class Title
 
     /**
      * Title Layout.
-     *
-     * @var ?Layout
      */
-    private $layout;
+    private ?Layout $layout;
 
     /**
      * Create a new Title.
@@ -81,7 +79,7 @@ public function getCaptionText(): string
      *
      * @return $this
      */
-    public function setCaption($caption)
+    public function setCaption($caption): static
     {
         $this->caption = $caption;
 
diff --git a/src/PhpSpreadsheet/Chart/TrendLine.php b/src/PhpSpreadsheet/Chart/TrendLine.php
index 75a5896c93..7ea2bde815 100644
--- a/src/PhpSpreadsheet/Chart/TrendLine.php
+++ b/src/PhpSpreadsheet/Chart/TrendLine.php
@@ -19,8 +19,7 @@ class TrendLine extends Properties
         self::TRENDLINE_MOVING_AVG,
     ];
 
-    /** @var string */
-    private $trendLineType = 'linear'; // TRENDLINE_LINEAR
+    private string $trendLineType = 'linear'; // TRENDLINE_LINEAR
 
     /** @var int */
     private $order = 2;
@@ -34,8 +33,7 @@ class TrendLine extends Properties
     /** @var bool */
     private $dispEq = false;
 
-    /** @var string */
-    private $name = '';
+    private string $name = '';
 
     /** @var float */
     private $backward = 0.0;
diff --git a/src/PhpSpreadsheet/Collection/Cells.php b/src/PhpSpreadsheet/Collection/Cells.php
index 9a9df227e6..e79a9df1f0 100644
--- a/src/PhpSpreadsheet/Collection/Cells.php
+++ b/src/PhpSpreadsheet/Collection/Cells.php
@@ -14,10 +14,7 @@ class Cells
 {
     protected const MAX_COLUMN_ID = 16384;
 
-    /**
-     * @var CacheInterface
-     */
-    private $cache;
+    private CacheInterface $cache;
 
     /**
      * Parent worksheet.
@@ -57,10 +54,8 @@ class Cells
 
     /**
      * Prefix used to uniquely identify cache data for this worksheet.
-     *
-     * @var string
      */
-    private $cachePrefix;
+    private string $cachePrefix;
 
     /**
      * Initialise this new cell collection.
@@ -112,7 +107,7 @@ public function update(Cell $cell): Cell
      *
      * @param string $cellCoordinate Coordinate of the cell to delete
      */
-    public function delete($cellCoordinate): void
+    public function delete(string $cellCoordinate): void
     {
         if ($cellCoordinate === $this->currentCoordinate && $this->currentCell !== null) {
             $this->currentCell->detach();
@@ -132,7 +127,7 @@ public function delete($cellCoordinate): void
      *
      * @return string[]
      */
-    public function getCoordinates()
+    public function getCoordinates(): array
     {
         return array_keys($this->index);
     }
@@ -142,7 +137,7 @@ public function getCoordinates()
      *
      * @return string[]
      */
-    public function getSortedCoordinates()
+    public function getSortedCoordinates(): array
     {
         asort($this->index);
 
@@ -188,7 +183,7 @@ public function getCurrentRow(): int
      *
      * @return array Highest column name and highest row number
      */
-    public function getHighestRowAndColumn()
+    public function getHighestRowAndColumn(): array
     {
         // Lookup highest column and highest row
         $maxRow = $maxColumn = 1;
@@ -270,7 +265,7 @@ public function getHighestRow($column = null)
      *
      * @return string Unique Reference
      */
-    private function getUniqueID()
+    private function getUniqueID(): string
     {
         $cacheType = Settings::getCache();
 
@@ -281,10 +276,8 @@ private function getUniqueID()
 
     /**
      * Clone the cell collection.
-     *
-     * @return self
      */
-    public function cloneCellCollection(Worksheet $worksheet)
+    public function cloneCellCollection(Worksheet $worksheet): static
     {
         $this->storeCurrentCell();
         $newCollection = clone $this;
@@ -381,10 +374,8 @@ private function destructIfNeeded(self $cells, string $message): void
      *
      * @param string $cellCoordinate Coordinate of the cell to update
      * @param Cell $cell Cell to update
-     *
-     * @return Cell
      */
-    public function add($cellCoordinate, Cell $cell)
+    public function add($cellCoordinate, Cell $cell): Cell
     {
         if ($cellCoordinate !== $this->currentCoordinate) {
             $this->storeCurrentCell();
@@ -408,7 +399,7 @@ public function add($cellCoordinate, Cell $cell)
      *
      * @return null|Cell Cell that was found, or null if not found
      */
-    public function get($cellCoordinate)
+    public function get(string $cellCoordinate)
     {
         if ($cellCoordinate === $this->currentCoordinate) {
             return $this->currentCell;
diff --git a/src/PhpSpreadsheet/Comment.php b/src/PhpSpreadsheet/Comment.php
index abadc7dfb8..7696092af8 100644
--- a/src/PhpSpreadsheet/Comment.php
+++ b/src/PhpSpreadsheet/Comment.php
@@ -14,38 +14,28 @@ class Comment implements IComparable
 {
     /**
      * Author.
-     *
-     * @var string
      */
-    private $author;
+    private string $author;
 
     /**
      * Rich text comment.
-     *
-     * @var RichText
      */
-    private $text;
+    private RichText $text;
 
     /**
      * Comment width (CSS style, i.e. XXpx or YYpt).
-     *
-     * @var string
      */
-    private $width = '96pt';
+    private string $width = '96pt';
 
     /**
      * Left margin (CSS style, i.e. XXpx or YYpt).
-     *
-     * @var string
      */
-    private $marginLeft = '59.25pt';
+    private string $marginLeft = '59.25pt';
 
     /**
      * Top margin (CSS style, i.e. XXpx or YYpt).
-     *
-     * @var string
      */
-    private $marginTop = '1.5pt';
+    private string $marginTop = '1.5pt';
 
     /**
      * Visible.
@@ -56,31 +46,23 @@ class Comment implements IComparable
 
     /**
      * Comment height (CSS style, i.e. XXpx or YYpt).
-     *
-     * @var string
      */
-    private $height = '55.5pt';
+    private string $height = '55.5pt';
 
     /**
      * Comment fill color.
-     *
-     * @var Color
      */
-    private $fillColor;
+    private Color $fillColor;
 
     /**
      * Alignment.
-     *
-     * @var string
      */
-    private $alignment;
+    private string $alignment;
 
     /**
      * Background image in comment.
-     *
-     * @var Drawing
      */
-    private $backgroundImage;
+    private Drawing $backgroundImage;
 
     /**
      * Create a new Comment.
diff --git a/src/PhpSpreadsheet/DefinedName.php b/src/PhpSpreadsheet/DefinedName.php
index 07433b1007..5c021e5b67 100644
--- a/src/PhpSpreadsheet/DefinedName.php
+++ b/src/PhpSpreadsheet/DefinedName.php
@@ -10,45 +10,33 @@ abstract class DefinedName
 
     /**
      * Name.
-     *
-     * @var string
      */
-    protected $name;
+    protected string $name;
 
     /**
      * Worksheet on which the defined name can be resolved.
-     *
-     * @var ?Worksheet
      */
-    protected $worksheet;
+    protected ?Worksheet $worksheet;
 
     /**
      * Value of the named object.
-     *
-     * @var string
      */
-    protected $value;
+    protected string $value;
 
     /**
      * Is the defined named local? (i.e. can only be used on $this->worksheet).
-     *
-     * @var bool
      */
-    protected $localOnly;
+    protected bool $localOnly;
 
     /**
      * Scope.
-     *
-     * @var ?Worksheet
      */
-    protected $scope;
+    protected ?Worksheet $scope;
 
     /**
      * Whether this is a named range or a named formula.
-     *
-     * @var bool
      */
-    protected $isFormula;
+    protected bool $isFormula;
 
     /**
      * Create a new Defined Name.
diff --git a/src/PhpSpreadsheet/Document/Properties.php b/src/PhpSpreadsheet/Document/Properties.php
index 65b079b351..a1c29fedb5 100644
--- a/src/PhpSpreadsheet/Document/Properties.php
+++ b/src/PhpSpreadsheet/Document/Properties.php
@@ -25,80 +25,58 @@ class Properties
 
     /**
      * Creator.
-     *
-     * @var string
      */
-    private $creator = 'Unknown Creator';
+    private string $creator = 'Unknown Creator';
 
     /**
      * LastModifiedBy.
-     *
-     * @var string
      */
-    private $lastModifiedBy;
+    private string $lastModifiedBy;
 
     /**
      * Created.
-     *
-     * @var float|int
      */
-    private $created;
+    private float|int $created;
 
     /**
      * Modified.
-     *
-     * @var float|int
      */
-    private $modified;
+    private float|int $modified;
 
     /**
      * Title.
-     *
-     * @var string
      */
-    private $title = 'Untitled Spreadsheet';
+    private string $title = 'Untitled Spreadsheet';
 
     /**
      * Description.
-     *
-     * @var string
      */
-    private $description = '';
+    private string $description = '';
 
     /**
      * Subject.
-     *
-     * @var string
      */
-    private $subject = '';
+    private string $subject = '';
 
     /**
      * Keywords.
-     *
-     * @var string
      */
-    private $keywords = '';
+    private string $keywords = '';
 
     /**
      * Category.
-     *
-     * @var string
      */
-    private $category = '';
+    private string $category = '';
 
     /**
      * Manager.
-     *
-     * @var string
      */
-    private $manager = '';
+    private string $manager = '';
 
     /**
      * Company.
-     *
-     * @var string
      */
-    private $company = '';
+    private string $company = '';
 
     /**
      * Custom Properties.
diff --git a/src/PhpSpreadsheet/Document/Security.php b/src/PhpSpreadsheet/Document/Security.php
index d94cf2a564..a97017b685 100644
--- a/src/PhpSpreadsheet/Document/Security.php
+++ b/src/PhpSpreadsheet/Document/Security.php
@@ -29,17 +29,13 @@ class Security
 
     /**
      * RevisionsPassword.
-     *
-     * @var string
      */
-    private $revisionsPassword = '';
+    private string $revisionsPassword = '';
 
     /**
      * WorkbookPassword.
-     *
-     * @var string
      */
-    private $workbookPassword = '';
+    private string $workbookPassword = '';
 
     /**
      * Create a new Document Security instance.
@@ -112,7 +108,7 @@ public function getRevisionsPassword(): string
      *
      * @return $this
      */
-    public function setRevisionsPassword(?string $password, bool $alreadyHashed = false)
+    public function setRevisionsPassword(?string $password, bool $alreadyHashed = false): static
     {
         if ($password !== null) {
             if (!$alreadyHashed) {
@@ -136,7 +132,7 @@ public function getWorkbookPassword(): string
      *
      * @return $this
      */
-    public function setWorkbookPassword(?string $password, bool $alreadyHashed = false)
+    public function setWorkbookPassword(?string $password, bool $alreadyHashed = false): static
     {
         if ($password !== null) {
             if (!$alreadyHashed) {
diff --git a/src/PhpSpreadsheet/HashTable.php b/src/PhpSpreadsheet/HashTable.php
index 6de7d03058..a66c9af562 100644
--- a/src/PhpSpreadsheet/HashTable.php
+++ b/src/PhpSpreadsheet/HashTable.php
@@ -101,20 +101,16 @@ public function clear(): void
 
     /**
      * Count.
-     *
-     * @return int
      */
-    public function count()
+    public function count(): int
     {
         return count($this->items);
     }
 
     /**
      * Get index for hash code.
-     *
-     * @return false|int Index
      */
-    public function getIndexForHashCode(string $hashCode)
+    public function getIndexForHashCode(string $hashCode): false|int
     {
         // Scrutinizer thinks the following could return string. It is wrong.
         return array_search($hashCode, $this->keyMap, true);
diff --git a/src/PhpSpreadsheet/Helper/Dimension.php b/src/PhpSpreadsheet/Helper/Dimension.php
index ff07ce5b8f..21dd4c5bb6 100644
--- a/src/PhpSpreadsheet/Helper/Dimension.php
+++ b/src/PhpSpreadsheet/Helper/Dimension.php
@@ -48,7 +48,7 @@ class Dimension
      *                If this is a height, then size is measured in pixels ()
      *                   or in points () if $unit is null.
      */
-    protected $size;
+    protected float|int $size;
 
     /**
      * @var null|string
diff --git a/src/PhpSpreadsheet/Helper/Html.php b/src/PhpSpreadsheet/Helper/Html.php
index 89c28dffa2..cbb55b9757 100644
--- a/src/PhpSpreadsheet/Helper/Html.php
+++ b/src/PhpSpreadsheet/Helper/Html.php
@@ -617,11 +617,9 @@ private function initialise(): void
     /**
      * Parse HTML formatting and return the resulting RichText.
      *
-     * @param string $html
-     *
      * @return RichText
      */
-    public function toRichTextObject($html)
+    public function toRichTextObject(string $html)
     {
         $this->initialise();
 
@@ -818,10 +816,7 @@ private function parseTextNode(DOMText $textNode): void
         $this->buildTextRun();
     }
 
-    /**
-     * @param string $callbackTag
-     */
-    private function handleCallback(DOMElement $element, $callbackTag, array $callbacks): void
+    private function handleCallback(DOMElement $element, string $callbackTag, array $callbacks): void
     {
         if (isset($callbacks[$callbackTag])) {
             $elementHandler = $callbacks[$callbackTag];
diff --git a/src/PhpSpreadsheet/Helper/Sample.php b/src/PhpSpreadsheet/Helper/Sample.php
index 6244375fe3..5deb9e202d 100644
--- a/src/PhpSpreadsheet/Helper/Sample.php
+++ b/src/PhpSpreadsheet/Helper/Sample.php
@@ -3,6 +3,7 @@
 namespace PhpOffice\PhpSpreadsheet\Helper;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
+use PhpOffice\PhpSpreadsheet\Chart\Renderer\MtJpGraphRenderer;
 use PhpOffice\PhpSpreadsheet\IOFactory;
 use PhpOffice\PhpSpreadsheet\Settings;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -23,50 +24,40 @@ class Sample
 {
     /**
      * Returns whether we run on CLI or browser.
-     *
-     * @return bool
      */
-    public function isCli()
+    public function isCli(): bool
     {
         return PHP_SAPI === 'cli';
     }
 
     /**
      * Return the filename currently being executed.
-     *
-     * @return string
      */
-    public function getScriptFilename()
+    public function getScriptFilename(): string
     {
         return basename($_SERVER['SCRIPT_FILENAME'], '.php');
     }
 
     /**
      * Whether we are executing the index page.
-     *
-     * @return bool
      */
-    public function isIndex()
+    public function isIndex(): bool
     {
         return $this->getScriptFilename() === 'index';
     }
 
     /**
      * Return the page title.
-     *
-     * @return string
      */
-    public function getPageTitle()
+    public function getPageTitle(): string
     {
         return $this->isIndex() ? 'PHPSpreadsheet' : $this->getScriptFilename();
     }
 
     /**
      * Return the page heading.
-     *
-     * @return string
      */
-    public function getPageHeading()
+    public function getPageHeading(): string
     {
         return $this->isIndex() ? '' : '<h1>' . str_replace('_', ' ', $this->getScriptFilename()) . '</h1>';
     }
@@ -76,7 +67,7 @@ public function getPageHeading()
      *
      * @return string[][] [$name => $path]
      */
-    public function getSamples()
+    public function getSamples(): array
     {
         // Populate samples
         $baseDir = realpath(__DIR__ . '/../../../samples');
@@ -154,10 +145,8 @@ protected function isDirOrMkdir(string $folder): bool
 
     /**
      * Returns the temporary directory and make sure it exists.
-     *
-     * @return string
      */
-    public function getTemporaryFolder()
+    public function getTemporaryFolder(): string
     {
         $tempFolder = sys_get_temp_dir() . '/phpspreadsheet';
         if (!$this->isDirOrMkdir($tempFolder)) {
@@ -171,9 +160,8 @@ public function getTemporaryFolder()
      * Returns the filename that should be used for sample output.
      *
      * @param string $filename
-     * @param string $extension
      */
-    public function getFilename($filename, $extension = 'xlsx'): string
+    public function getFilename($filename, string $extension = 'xlsx'): string
     {
         $originalExtension = pathinfo($filename, PATHINFO_EXTENSION);
 
@@ -182,12 +170,8 @@ public function getFilename($filename, $extension = 'xlsx'): string
 
     /**
      * Return a random temporary file name.
-     *
-     * @param string $extension
-     *
-     * @return string
      */
-    public function getTemporaryFilename($extension = 'xlsx')
+    public function getTemporaryFilename(string $extension = 'xlsx'): string
     {
         $temporaryFilename = tempnam($this->getTemporaryFolder(), 'phpspreadsheet-');
         if ($temporaryFilename === false) {
@@ -212,7 +196,7 @@ public function renderChart(Chart $chart, string $fileName): void
             return;
         }
 
-        Settings::setChartRenderer(\PhpOffice\PhpSpreadsheet\Chart\Renderer\MtJpGraphRenderer::class);
+        Settings::setChartRenderer(MtJpGraphRenderer::class);
 
         $fileName = $this->getFilename($fileName, 'png');
 
diff --git a/src/PhpSpreadsheet/Helper/Size.php b/src/PhpSpreadsheet/Helper/Size.php
index 12ba4ef732..3659485ede 100644
--- a/src/PhpSpreadsheet/Helper/Size.php
+++ b/src/PhpSpreadsheet/Helper/Size.php
@@ -6,20 +6,11 @@ class Size
 {
     const REGEXP_SIZE_VALIDATION = '/^(?P<size>\d*\.?\d+)(?P<unit>pt|px|em)?$/i';
 
-    /**
-     * @var bool
-     */
-    protected $valid;
+    protected bool $valid;
 
-    /**
-     * @var string
-     */
-    protected $size = '';
+    protected string $size = '';
 
-    /**
-     * @var string
-     */
-    protected $unit = '';
+    protected string $unit = '';
 
     public function __construct(string $size)
     {
@@ -45,7 +36,7 @@ public function unit(): string
         return $this->unit;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->size . $this->unit;
     }
diff --git a/src/PhpSpreadsheet/Helper/TextGrid.php b/src/PhpSpreadsheet/Helper/TextGrid.php
index 3a4a98f022..8088560d02 100644
--- a/src/PhpSpreadsheet/Helper/TextGrid.php
+++ b/src/PhpSpreadsheet/Helper/TextGrid.php
@@ -4,25 +4,13 @@
 
 class TextGrid
 {
-    /**
-     * @var bool
-     */
-    private $isCli = true;
+    private bool $isCli;
 
-    /**
-     * @var array
-     */
-    protected $matrix;
+    protected array $matrix;
 
-    /**
-     * @var array
-     */
-    protected $rows;
+    protected array $rows;
 
-    /**
-     * @var array
-     */
-    protected $columns;
+    protected array $columns;
 
     /**
      * @var string
diff --git a/src/PhpSpreadsheet/IOFactory.php b/src/PhpSpreadsheet/IOFactory.php
index c088397d81..a133f1c46e 100644
--- a/src/PhpSpreadsheet/IOFactory.php
+++ b/src/PhpSpreadsheet/IOFactory.php
@@ -139,7 +139,7 @@ public static function createReaderForFile(string $filename, ?array $readers = n
             $readers = array_map('strtoupper', $readers);
             $testReaders = array_filter(
                 self::$readers,
-                function (string $readerType) use ($readers) {
+                function (string $readerType) use ($readers): bool {
                     return in_array(strtoupper($readerType), $readers, true);
                 },
                 ARRAY_FILTER_USE_KEY
diff --git a/src/PhpSpreadsheet/Reader/BaseReader.php b/src/PhpSpreadsheet/Reader/BaseReader.php
index d395f8f3a2..b8e6a81a9b 100644
--- a/src/PhpSpreadsheet/Reader/BaseReader.php
+++ b/src/PhpSpreadsheet/Reader/BaseReader.php
@@ -55,10 +55,7 @@ abstract class BaseReader implements IReader
     /** @var resource */
     protected $fileHandle;
 
-    /**
-     * @var ?XmlScanner
-     */
-    protected $securityScanner;
+    protected ?XmlScanner $securityScanner = null;
 
     public function __construct()
     {
@@ -207,12 +204,8 @@ protected function openFile(string $filename): void
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         throw new PhpSpreadsheetException('Reader classes must implement their own listWorksheetInfo() method');
     }
@@ -222,12 +215,8 @@ public function listWorksheetInfo($filename)
      * possibly without parsing the whole file to a Spreadsheet object.
      * Readers will often have a more efficient method with which
      * they can override this method.
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetNames($filename)
+    public function listWorksheetNames(string $filename): array
     {
         $returnArray = [];
         $info = $this->listWorksheetInfo($filename);
diff --git a/src/PhpSpreadsheet/Reader/Csv.php b/src/PhpSpreadsheet/Reader/Csv.php
index 10107e237c..bf6d0ab1d6 100644
--- a/src/PhpSpreadsheet/Reader/Csv.php
+++ b/src/PhpSpreadsheet/Reader/Csv.php
@@ -33,10 +33,8 @@ class Csv extends BaseReader
 
     /**
      * Input encoding.
-     *
-     * @var string
      */
-    private $inputEncoding = 'UTF-8';
+    private string $inputEncoding = 'UTF-8';
 
     /**
      * Fallback encoding if guess strikes out.
@@ -47,17 +45,13 @@ class Csv extends BaseReader
 
     /**
      * Delimiter.
-     *
-     * @var ?string
      */
-    private $delimiter;
+    private ?string $delimiter = null;
 
     /**
      * Enclosure.
-     *
-     * @var string
      */
-    private $enclosure = '"';
+    private string $enclosure = '"';
 
     /**
      * Sheet index to read.
@@ -75,10 +69,8 @@ class Csv extends BaseReader
 
     /**
      * The character that can escape the enclosure.
-     *
-     * @var string
      */
-    private $escapeCharacter = '\\';
+    private string $escapeCharacter = '\\';
 
     /**
      * Callback for setting defaults in construction.
@@ -224,12 +216,8 @@ protected function inferSeparator(): void
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         // Open file
         $this->openFileOrMemory($filename);
diff --git a/src/PhpSpreadsheet/Reader/Csv/Delimiter.php b/src/PhpSpreadsheet/Reader/Csv/Delimiter.php
index 029d4a186e..102259822a 100644
--- a/src/PhpSpreadsheet/Reader/Csv/Delimiter.php
+++ b/src/PhpSpreadsheet/Reader/Csv/Delimiter.php
@@ -9,11 +9,9 @@ class Delimiter
     /** @var resource */
     protected $fileHandle;
 
-    /** @var string */
-    protected $escapeCharacter;
+    protected string $escapeCharacter;
 
-    /** @var string */
-    protected $enclosure;
+    protected string $enclosure;
 
     /** @var array */
     protected $counts = [];
@@ -92,7 +90,7 @@ public function infer(): ?string
 
             $meanSquareDeviations[$delimiter] = array_reduce(
                 $series,
-                function ($sum, $value) use ($median) {
+                function ($sum, $value) use ($median): int|float {
                     return $sum + ($value - $median) ** 2;
                 }
             ) / count($series);
diff --git a/src/PhpSpreadsheet/Reader/DefaultReadFilter.php b/src/PhpSpreadsheet/Reader/DefaultReadFilter.php
index 8fdb162b4c..bfabb07fa0 100644
--- a/src/PhpSpreadsheet/Reader/DefaultReadFilter.php
+++ b/src/PhpSpreadsheet/Reader/DefaultReadFilter.php
@@ -10,10 +10,8 @@ class DefaultReadFilter implements IReadFilter
      * @param string $columnAddress Column address (as a string value like "A", or "IV")
      * @param int $row Row number
      * @param string $worksheetName Optional worksheet name
-     *
-     * @return bool
      */
-    public function readCell($columnAddress, $row, $worksheetName = '')
+    public function readCell($columnAddress, $row, $worksheetName = ''): bool
     {
         return true;
     }
diff --git a/src/PhpSpreadsheet/Reader/Gnumeric.php b/src/PhpSpreadsheet/Reader/Gnumeric.php
index 99e4d6ad6c..4915be75a6 100644
--- a/src/PhpSpreadsheet/Reader/Gnumeric.php
+++ b/src/PhpSpreadsheet/Reader/Gnumeric.php
@@ -48,8 +48,7 @@ class Gnumeric extends BaseReader
      */
     private $spreadsheet;
 
-    /** @var ReferenceHelper */
-    private $referenceHelper;
+    private ReferenceHelper $referenceHelper;
 
     /** @var array */
     public static $mappings = [
@@ -100,12 +99,8 @@ private static function matchXml(XMLReader $xml, string $expectedLocalName): boo
 
     /**
      * Reads names of the worksheets from a file, without parsing the whole file to a Spreadsheet object.
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetNames($filename)
+    public function listWorksheetNames(string $filename): array
     {
         File::assertFile($filename);
         if (!$this->canRead($filename)) {
@@ -133,12 +128,8 @@ public function listWorksheetNames($filename)
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         File::assertFile($filename);
         if (!$this->canRead($filename)) {
@@ -186,10 +177,8 @@ public function listWorksheetInfo($filename)
 
     /**
      * @param string $filename
-     *
-     * @return string
      */
-    private function gzfileGetContents($filename)
+    private function gzfileGetContents($filename): string
     {
         $data = '';
         $contents = @file_get_contents($filename);
@@ -533,7 +522,7 @@ private function processDefinedNames(?SimpleXMLElement $gnmXML): void
             foreach ($gnmXML->Names->Name as $definedName) {
                 $name = (string) $definedName->name;
                 $value = (string) $definedName->value;
-                if (stripos($value, '#REF!') !== false) {
+                if (stripos($value, '#REF!') !== false || empty($value)) {
                     continue;
                 }
 
diff --git a/src/PhpSpreadsheet/Reader/Gnumeric/PageSetup.php b/src/PhpSpreadsheet/Reader/Gnumeric/PageSetup.php
index 0257fc9a4f..f12b742f35 100644
--- a/src/PhpSpreadsheet/Reader/Gnumeric/PageSetup.php
+++ b/src/PhpSpreadsheet/Reader/Gnumeric/PageSetup.php
@@ -10,10 +10,7 @@
 
 class PageSetup
 {
-    /**
-     * @var Spreadsheet
-     */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     public function __construct(Spreadsheet $spreadsheet)
     {
diff --git a/src/PhpSpreadsheet/Reader/Gnumeric/Properties.php b/src/PhpSpreadsheet/Reader/Gnumeric/Properties.php
index 23d4067b9d..a60b453482 100644
--- a/src/PhpSpreadsheet/Reader/Gnumeric/Properties.php
+++ b/src/PhpSpreadsheet/Reader/Gnumeric/Properties.php
@@ -8,10 +8,7 @@
 
 class Properties
 {
-    /**
-     * @var Spreadsheet
-     */
-    protected $spreadsheet;
+    protected Spreadsheet $spreadsheet;
 
     public function __construct(Spreadsheet $spreadsheet)
     {
diff --git a/src/PhpSpreadsheet/Reader/Gnumeric/Styles.php b/src/PhpSpreadsheet/Reader/Gnumeric/Styles.php
index dc44dcc23e..dd082b2764 100644
--- a/src/PhpSpreadsheet/Reader/Gnumeric/Styles.php
+++ b/src/PhpSpreadsheet/Reader/Gnumeric/Styles.php
@@ -14,15 +14,9 @@
 
 class Styles
 {
-    /**
-     * @var Spreadsheet
-     */
-    private $spreadsheet;
-
-    /**
-     * @var bool
-     */
-    protected $readDataOnly = false;
+    private Spreadsheet $spreadsheet;
+
+    protected bool $readDataOnly;
 
     /** @var array */
     public static $mappings = [
diff --git a/src/PhpSpreadsheet/Reader/Html.php b/src/PhpSpreadsheet/Reader/Html.php
index fa49a79f01..ba6370b6ce 100644
--- a/src/PhpSpreadsheet/Reader/Html.php
+++ b/src/PhpSpreadsheet/Reader/Html.php
@@ -223,7 +223,7 @@ public function loadSpreadsheetFromFile(string $filename): Spreadsheet
      *
      * @deprecated no use is made of this property
      */
-    public function setInputEncoding($inputEncoding)
+    public function setInputEncoding($inputEncoding): static
     {
         $this->inputEncoding = $inputEncoding;
 
@@ -281,11 +281,10 @@ protected function releaseTableStartColumn(): string
     /**
      * Flush cell.
      *
-     * @param string $column
      * @param int|string $row
      * @param mixed $cellContent
      */
-    protected function flushCell(Worksheet $sheet, $column, $row, &$cellContent, array $attributeArray): void
+    protected function flushCell(Worksheet $sheet, string $column, $row, &$cellContent, array $attributeArray): void
     {
         if (is_string($cellContent)) {
             //    Simple String content
@@ -663,12 +662,8 @@ protected function processDomElement(DOMNode $element, Worksheet $sheet, int &$r
 
     /**
      * Loads PhpSpreadsheet from file into PhpSpreadsheet instance.
-     *
-     * @param string $filename
-     *
-     * @return Spreadsheet
      */
-    public function loadIntoExisting($filename, Spreadsheet $spreadsheet)
+    public function loadIntoExisting(string $filename, Spreadsheet $spreadsheet): Spreadsheet
     {
         // Validate
         if (!$this->canRead($filename)) {
@@ -863,7 +858,7 @@ public function getSheetIndex()
      *
      * @return $this
      */
-    public function setSheetIndex($sheetIndex)
+    public function setSheetIndex($sheetIndex): static
     {
         $this->sheetIndex = $sheetIndex;
 
@@ -881,10 +876,8 @@ public function setSheetIndex($sheetIndex)
      * - Implement to other propertie, such as border
      *
      * @param int $row
-     * @param string $column
-     * @param array $attributeArray
      */
-    private function applyInlineStyle(Worksheet &$sheet, $row, $column, $attributeArray): void
+    private function applyInlineStyle(Worksheet &$sheet, $row, string $column, array $attributeArray): void
     {
         if (!isset($attributeArray['style'])) {
             return;
@@ -1062,10 +1055,8 @@ private function applyInlineStyle(Worksheet &$sheet, $row, $column, $attributeAr
      * Check if has #, so we can get clean hex.
      *
      * @param mixed $value
-     *
-     * @return null|string
      */
-    public function getStyleColor($value)
+    public function getStyleColor($value): string
     {
         $value = (string) $value;
         if (strpos($value, '#') === 0) {
@@ -1075,11 +1066,7 @@ public function getStyleColor($value)
         return \PhpOffice\PhpSpreadsheet\Helper\Html::colourNameLookup($value);
     }
 
-    /**
-     * @param string    $column
-     * @param int       $row
-     */
-    private function insertImage(Worksheet $sheet, $column, $row, array $attributes): void
+    private function insertImage(Worksheet $sheet, string $column, int $row, array $attributes): void
     {
         if (!isset($attributes['src'])) {
             return;
@@ -1145,19 +1132,13 @@ public static function getBorderMappings(): array
      * Map html border style to PhpSpreadsheet border style.
      *
      * @param  string $style
-     *
-     * @return null|string
      */
-    public function getBorderStyle($style)
+    public function getBorderStyle($style): ?string
     {
         return self::BORDER_MAPPINGS[$style] ?? null;
     }
 
-    /**
-     * @param string $styleValue
-     * @param string $type
-     */
-    private function setBorderStyle(Style $cellStyle, $styleValue, $type): void
+    private function setBorderStyle(Style $cellStyle, string $styleValue, string $type): void
     {
         if (trim($styleValue) === Border::BORDER_NONE) {
             $borderStyle = Border::BORDER_NONE;
@@ -1186,12 +1167,8 @@ private function setBorderStyle(Style $cellStyle, $styleValue, $type): void
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         $info = [];
         $spreadsheet = new Spreadsheet();
diff --git a/src/PhpSpreadsheet/Reader/IReader.php b/src/PhpSpreadsheet/Reader/IReader.php
index 97afe3cb20..dadf36ff90 100644
--- a/src/PhpSpreadsheet/Reader/IReader.php
+++ b/src/PhpSpreadsheet/Reader/IReader.php
@@ -2,6 +2,8 @@
 
 namespace PhpOffice\PhpSpreadsheet\Reader;
 
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+
 interface IReader
 {
     public const LOAD_WITH_CHARTS = 1;
@@ -137,7 +139,7 @@ public function setReadFilter(IReadFilter $readFilter);
      *            self::SKIP_EMPTY_CELLS    Don't read empty cells (cells that contain a null value,
      *                                      empty string, or a string containing only whitespace characters)
      *
-     * @return \PhpOffice\PhpSpreadsheet\Spreadsheet
+     * @return Spreadsheet
      */
     public function load(string $filename, int $flags = 0);
 }
diff --git a/src/PhpSpreadsheet/Reader/Ods.php b/src/PhpSpreadsheet/Reader/Ods.php
index 30fc36d914..719dd67ac2 100644
--- a/src/PhpSpreadsheet/Reader/Ods.php
+++ b/src/PhpSpreadsheet/Reader/Ods.php
@@ -88,11 +88,9 @@ public function canRead(string $filename): bool
     /**
      * Reads names of the worksheets from a file, without parsing the whole file to a PhpSpreadsheet object.
      *
-     * @param string $filename
-     *
      * @return string[]
      */
-    public function listWorksheetNames($filename)
+    public function listWorksheetNames(string $filename): array
     {
         File::assertFile($filename, self::INITIAL_FILE);
 
@@ -138,12 +136,8 @@ public function listWorksheetNames($filename)
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         File::assertFile($filename, self::INITIAL_FILE);
 
@@ -248,12 +242,8 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
 
     /**
      * Loads PhpSpreadsheet from file into PhpSpreadsheet instance.
-     *
-     * @param string $filename
-     *
-     * @return Spreadsheet
      */
-    public function loadIntoExisting($filename, Spreadsheet $spreadsheet)
+    public function loadIntoExisting(string $filename, Spreadsheet $spreadsheet): Spreadsheet
     {
         File::assertFile($filename, self::INITIAL_FILE);
 
@@ -734,10 +724,8 @@ private function setSelected(Spreadsheet $spreadsheet, string $wsname, string $s
 
     /**
      * Recursively scan element.
-     *
-     * @return string
      */
-    protected function scanElementForText(DOMNode $element)
+    protected function scanElementForText(DOMNode $element): string
     {
         $str = '';
         foreach ($element->childNodes as $child) {
@@ -774,12 +762,7 @@ private static function getMultiplier(?DOMAttr $cAttr): int
         return $multiplier;
     }
 
-    /**
-     * @param string $is
-     *
-     * @return RichText
-     */
-    private function parseRichText($is)
+    private function parseRichText(string $is): RichText
     {
         $value = new RichText();
         $value->createText($is);
diff --git a/src/PhpSpreadsheet/Reader/Ods/BaseLoader.php b/src/PhpSpreadsheet/Reader/Ods/BaseLoader.php
index b06691f42a..c280c4ec56 100644
--- a/src/PhpSpreadsheet/Reader/Ods/BaseLoader.php
+++ b/src/PhpSpreadsheet/Reader/Ods/BaseLoader.php
@@ -7,15 +7,9 @@
 
 abstract class BaseLoader
 {
-    /**
-     * @var Spreadsheet
-     */
-    protected $spreadsheet;
+    protected Spreadsheet $spreadsheet;
 
-    /**
-     * @var string
-     */
-    protected $tableNs;
+    protected string $tableNs;
 
     public function __construct(Spreadsheet $spreadsheet, string $tableNs)
     {
diff --git a/src/PhpSpreadsheet/Reader/Ods/DefinedNames.php b/src/PhpSpreadsheet/Reader/Ods/DefinedNames.php
index e0ab8900aa..a99e3ea743 100644
--- a/src/PhpSpreadsheet/Reader/Ods/DefinedNames.php
+++ b/src/PhpSpreadsheet/Reader/Ods/DefinedNames.php
@@ -25,6 +25,7 @@ protected function readDefinedRanges(DOMElement $workbookData): void
             $baseAddress = $definedNameElement->getAttributeNS($this->tableNs, 'base-cell-address');
             $range = $definedNameElement->getAttributeNS($this->tableNs, 'cell-range-address');
 
+            /** @var non-empty-string $baseAddress */
             $baseAddress = FormulaTranslator::convertToExcelAddressValue($baseAddress);
             $range = FormulaTranslator::convertToExcelAddressValue($range);
 
@@ -43,6 +44,7 @@ protected function readDefinedExpressions(DOMElement $workbookData): void
             $baseAddress = $definedNameElement->getAttributeNS($this->tableNs, 'base-cell-address');
             $expression = $definedNameElement->getAttributeNS($this->tableNs, 'expression');
 
+            /** @var non-empty-string $baseAddress */
             $baseAddress = FormulaTranslator::convertToExcelAddressValue($baseAddress);
             $expression = substr($expression, strpos($expression, ':=') + 1);
             $expression = FormulaTranslator::convertToExcelFormulaValue($expression);
@@ -53,6 +55,8 @@ protected function readDefinedExpressions(DOMElement $workbookData): void
 
     /**
      * Assess scope and store the Defined Name.
+     *
+     * @param non-empty-string $baseAddress
      */
     private function addDefinedName(string $baseAddress, string $definedName, string $value): void
     {
diff --git a/src/PhpSpreadsheet/Reader/Ods/Properties.php b/src/PhpSpreadsheet/Reader/Ods/Properties.php
index 33419356e2..46864d0af0 100644
--- a/src/PhpSpreadsheet/Reader/Ods/Properties.php
+++ b/src/PhpSpreadsheet/Reader/Ods/Properties.php
@@ -8,8 +8,7 @@
 
 class Properties
 {
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     public function __construct(Spreadsheet $spreadsheet)
     {
@@ -106,9 +105,8 @@ private function setMetaProperties(
 
     /**
      * @param mixed $propertyValueAttributes
-     * @param mixed $propertyValue
      */
-    private function setUserDefinedProperty($propertyValueAttributes, $propertyValue, DocumentProperties $docProps): void
+    private function setUserDefinedProperty($propertyValueAttributes, string $propertyValue, DocumentProperties $docProps): void
     {
         $propertyValueName = '';
         $propertyValueType = DocumentProperties::PROPERTY_TYPE_STRING;
diff --git a/src/PhpSpreadsheet/Reader/Slk.php b/src/PhpSpreadsheet/Reader/Slk.php
index 64c3bb8ee2..7170a2a914 100644
--- a/src/PhpSpreadsheet/Reader/Slk.php
+++ b/src/PhpSpreadsheet/Reader/Slk.php
@@ -8,6 +8,7 @@
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PhpOffice\PhpSpreadsheet\Style\Border;
+use PhpOffice\PhpSpreadsheet\Style\Fill;
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 
 class Slk extends BaseReader
@@ -108,7 +109,7 @@ private function canReadOrBust(string $filename): void
      *
      * @codeCoverageIgnore
      */
-    public function setInputEncoding($inputEncoding)
+    public function setInputEncoding($inputEncoding): static
     {
         $this->inputEncoding = $inputEncoding;
 
@@ -131,12 +132,8 @@ public function getInputEncoding()
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         // Open file
         $this->canReadOrBust($filename);
@@ -380,7 +377,7 @@ private function styleSettings(string $rowDatum, array &$styleData, string &$fon
             } elseif (array_key_exists($char, self::STYLE_SETTINGS_BORDER)) {
                 $styleData['borders'][self::STYLE_SETTINGS_BORDER[$char]]['borderStyle'] = Border::BORDER_THIN;
             } elseif ($char == 'S') {
-                $styleData['fill']['fillType'] = \PhpOffice\PhpSpreadsheet\Style\Fill::FILL_PATTERN_GRAY125;
+                $styleData['fill']['fillType'] = Fill::FILL_PATTERN_GRAY125;
             } elseif ($char == 'M') {
                 if (preg_match('/M([1-9]\\d*)/', $styleSettings, $matches)) {
                     $fontStyle = $matches[1];
@@ -504,11 +501,9 @@ private function processPFinal(Spreadsheet &$spreadsheet, array $formatArray): v
     /**
      * Loads PhpSpreadsheet from file into PhpSpreadsheet instance.
      *
-     * @param string $filename
-     *
      * @return Spreadsheet
      */
-    public function loadIntoExisting($filename, Spreadsheet $spreadsheet)
+    public function loadIntoExisting(string $filename, Spreadsheet $spreadsheet)
     {
         // Open file
         $this->canReadOrBust($filename);
@@ -585,7 +580,7 @@ public function getSheetIndex()
      *
      * @return $this
      */
-    public function setSheetIndex($sheetIndex)
+    public function setSheetIndex($sheetIndex): static
     {
         $this->sheetIndex = $sheetIndex;
 
diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index 76eccfbffb..a1ab019ace 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -33,6 +33,7 @@
 use PhpOffice\PhpSpreadsheet\Worksheet\MemoryDrawing;
 use PhpOffice\PhpSpreadsheet\Worksheet\PageSetup;
 use PhpOffice\PhpSpreadsheet\Worksheet\SheetView;
+use PhpOffice\PhpSpreadsheet\Worksheet\Table;
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 
 // Original file header of ParseXL (used as the base for this class):
@@ -218,10 +219,8 @@ class Xls extends BaseReader
     /**
      * Codepage set in the Excel file being read. Only important for BIFF5 (Excel 5.0 - Excel 95)
      * For BIFF8 (Excel 97 - Excel 2003) this will always have the value 'UTF-16LE'.
-     *
-     * @var string
      */
-    private $codepage = '';
+    private string $codepage = '';
 
     /**
      * Shared formats.
@@ -469,12 +468,8 @@ public function getCodepage(): string
 
     /**
      * Reads names of the worksheets from a file, without parsing the whole file to a PhpSpreadsheet object.
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetNames($filename)
+    public function listWorksheetNames(string $filename): array
     {
         File::assertFile($filename);
 
@@ -531,12 +526,8 @@ public function listWorksheetNames($filename)
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         File::assertFile($filename);
 
@@ -1258,18 +1249,17 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
                         $ranges = explode(',', $definedName['formula']); // FIXME: what if sheetname contains comma?
 
                         $extractedRanges = [];
+                        /** @var non-empty-string $range */
                         foreach ($ranges as $range) {
                             // $range should look like one of these
                             //        Foo!$C$7:$J$66
                             //        Bar!$A$1:$IV$2
                             $explodes = Worksheet::extractSheetTitle($range, true);
                             $sheetName = trim($explodes[0], "'");
-                            if (count($explodes) == 2) {
-                                if (strpos($explodes[1], ':') === false) {
-                                    $explodes[1] = $explodes[1] . ':' . $explodes[1];
-                                }
-                                $extractedRanges[] = str_replace('$', '', $explodes[1]); // C7:J66
+                            if (strpos($explodes[1], ':') === false) {
+                                $explodes[1] = $explodes[1] . ':' . $explodes[1];
                             }
+                            $extractedRanges[] = str_replace('$', '', $explodes[1]); // C7:J66
                         }
                         if ($docSheet = $this->spreadsheet->getSheetByName($sheetName)) {
                             $docSheet->getPageSetup()->setPrintArea(implode(',', $extractedRanges)); // C7:J66,A1:IV2
@@ -1319,8 +1309,10 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
                 }
             } else {
                 // Extract range
-                if (strpos($definedName['formula'], '!') !== false) {
-                    $explodes = Worksheet::extractSheetTitle($definedName['formula'], true);
+                /** @var non-empty-string $formula */
+                $formula = $definedName['formula'];
+                if (strpos($formula, '!') !== false) {
+                    $explodes = Worksheet::extractSheetTitle($formula, true);
                     if (
                         ($docSheet = $this->spreadsheet->getSheetByName($explodes[0])) ||
                         ($docSheet = $this->spreadsheet->getSheetByName(trim($explodes[0], "'")))
@@ -1335,7 +1327,7 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
                     }
                 }
                 //    Named Value
-                    //    TODO Provide support for named values
+                //    TODO Provide support for named values
             }
         }
         $this->data = '';
@@ -1352,7 +1344,7 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
      *
      * @return string Record data
      */
-    private function readRecordData($data, $pos, $len)
+    private function readRecordData($data, int $pos, int $len): string
     {
         $data = substr($data, $pos, $len);
 
@@ -1401,10 +1393,8 @@ private function readRecordData($data, $pos, $len)
 
     /**
      * Use OLE reader to extract the relevant data streams from the OLE file.
-     *
-     * @param string $filename
      */
-    private function loadOLE($filename): void
+    private function loadOLE(string $filename): void
     {
         // OLE reader
         $ole = new OLERead();
@@ -1898,10 +1888,8 @@ private function readFilepass(): void
      *
      * @param int $block Block for which to create decrypto
      * @param string $valContext MD5 context state
-     *
-     * @return Xls\RC4
      */
-    private function makeKey($block, $valContext)
+    private function makeKey(int $block, $valContext): Xls\RC4
     {
         $pwarray = str_repeat("\0", 64);
 
@@ -1936,7 +1924,7 @@ private function makeKey($block, $valContext)
      *
      * @return bool Success
      */
-    private function verifyPassword($password, $docid, $salt_data, $hashedsalt_data, &$valContext)
+    private function verifyPassword(string $password, string $docid, string $salt_data, string $hashedsalt_data, &$valContext): bool
     {
         $pwarray = str_repeat("\0", 64);
 
@@ -3072,7 +3060,7 @@ private function readSst(): void
                         $len = min($charsLeft, $limitpos - $pos);
                         for ($j = 0; $j < $len; ++$j) {
                             $retstr .= $recordData[$pos + $j]
-                            . chr(0);
+                                . chr(0);
                         }
                         $charsLeft -= $len;
                         $isCompressed = false;
@@ -5198,10 +5186,8 @@ private function readContinue(): void
      * records are found. Splices the record data pieces and returns the combined string as if record data
      * is in one piece.
      * Moves to next current position in data stream to start of next record different from a CONtINUE record.
-     *
-     * @return array
      */
-    private function getSplicedRecordData()
+    private function getSplicedRecordData(): array
     {
         $data = '';
         $spliceOffsets = [];
@@ -5238,7 +5224,7 @@ private function getSplicedRecordData()
      *
      * @return string Human readable formula
      */
-    private function getFormulaFromStructure($formulaStructure, $baseCell = 'A1')
+    private function getFormulaFromStructure($formulaStructure, $baseCell = 'A1'): string
     {
         // offset: 0; size: 2; size of the following formula data
         $sz = self::getUInt2d($formulaStructure, 0);
@@ -5265,7 +5251,7 @@ private function getFormulaFromStructure($formulaStructure, $baseCell = 'A1')
      *
      * @return string Human readable formula
      */
-    private function getFormulaFromData($formulaData, $additionalData = '', $baseCell = 'A1')
+    private function getFormulaFromData(string $formulaData, string $additionalData = '', string $baseCell = 'A1'): string
     {
         // start parsing the formula data
         $tokens = [];
@@ -5283,12 +5269,11 @@ private function getFormulaFromData($formulaData, $additionalData = '', $baseCel
     /**
      * Take array of tokens together with additional data for formula and return human readable formula.
      *
-     * @param array $tokens
      * @param string $additionalData Additional binary data going with the formula
      *
      * @return string Human readable formula
      */
-    private function createFormulaFromTokens($tokens, $additionalData)
+    private function createFormulaFromTokens(array $tokens, string $additionalData): string
     {
         // empty formula?
         if (empty($tokens)) {
@@ -5460,10 +5445,8 @@ private function createFormulaFromTokens($tokens, $additionalData)
      *
      * @param string $formulaData Formula data
      * @param string $baseCell Base cell, only needed when formula contains tRefN tokens, e.g. with shared formulas
-     *
-     * @return array
      */
-    private function getNextToken($formulaData, $baseCell = 'A1')
+    private function getNextToken(string $formulaData, string $baseCell = 'A1'): array
     {
         // offset: 0; size: 1; token id
         $id = ord($formulaData[0]); // token id
@@ -7040,12 +7023,8 @@ private function getNextToken($formulaData, $baseCell = 'A1')
     /**
      * Reads a cell address in BIFF8 e.g. 'A2' or '$A$2'
      * section 3.3.4.
-     *
-     * @param string $cellAddressStructure
-     *
-     * @return string
      */
-    private function readBIFF8CellAddress($cellAddressStructure)
+    private function readBIFF8CellAddress(string $cellAddressStructure): string
     {
         // offset: 0; size: 2; index to row (0... 65535) (or offset (-32768... 32767))
         $row = self::getUInt2d($cellAddressStructure, 0) + 1;
@@ -7071,12 +7050,9 @@ private function readBIFF8CellAddress($cellAddressStructure)
      * to indicate offsets from a base cell
      * section 3.3.4.
      *
-     * @param string $cellAddressStructure
      * @param string $baseCell Base cell, only needed when formula contains tRefN tokens, e.g. with shared formulas
-     *
-     * @return string
      */
-    private function readBIFF8CellAddressB($cellAddressStructure, $baseCell = 'A1')
+    private function readBIFF8CellAddressB(string $cellAddressStructure, $baseCell = 'A1'): string
     {
         [$baseCol, $baseRow] = Coordinate::coordinateFromString($baseCell);
         $baseCol = Coordinate::columnIndexFromString($baseCol) - 1;
@@ -7119,12 +7095,8 @@ private function readBIFF8CellAddressB($cellAddressStructure, $baseCell = 'A1')
      * Reads a cell range address in BIFF5 e.g. 'A2:B6' or 'A1'
      * always fixed range
      * section 2.5.14.
-     *
-     * @param string $subData
-     *
-     * @return string
      */
-    private function readBIFF5CellRangeAddressFixed($subData)
+    private function readBIFF5CellRangeAddressFixed(string $subData): string
     {
         // offset: 0; size: 2; index to first row
         $fr = self::getUInt2d($subData, 0) + 1;
@@ -7158,12 +7130,8 @@ private function readBIFF5CellRangeAddressFixed($subData)
      * Reads a cell range address in BIFF8 e.g. 'A2:B6' or 'A1'
      * always fixed range
      * section 2.5.14.
-     *
-     * @param string $subData
-     *
-     * @return string
      */
-    private function readBIFF8CellRangeAddressFixed($subData)
+    private function readBIFF8CellRangeAddressFixed(string $subData): string
     {
         // offset: 0; size: 2; index to first row
         $fr = self::getUInt2d($subData, 0) + 1;
@@ -7197,12 +7165,8 @@ private function readBIFF8CellRangeAddressFixed($subData)
      * Reads a cell range address in BIFF8 e.g. 'A2:B6' or '$A$2:$B$6'
      * there are flags indicating whether column/row index is relative
      * section 3.3.4.
-     *
-     * @param string $subData
-     *
-     * @return string
      */
-    private function readBIFF8CellRangeAddress($subData)
+    private function readBIFF8CellRangeAddress(string $subData): string
     {
         // todo: if cell range is just a single cell, should this funciton
         // not just return e.g. 'A1' and not 'A1:A1' ?
@@ -7251,12 +7215,11 @@ private function readBIFF8CellRangeAddress($subData)
      * to indicate offsets from a base cell
      * section 3.3.4.
      *
-     * @param string $subData
      * @param string $baseCell Base cell
      *
      * @return string Cell range address
      */
-    private function readBIFF8CellRangeAddressB($subData, $baseCell = 'A1')
+    private function readBIFF8CellRangeAddressB(string $subData, string $baseCell = 'A1'): string
     {
         [$baseCol, $baseRow] = Coordinate::indexesFromString($baseCell);
         $baseCol = $baseCol - 1;
@@ -7336,12 +7299,8 @@ private function readBIFF8CellRangeAddressB($subData, $baseCell = 'A1')
     /**
      * Read BIFF8 cell range address list
      * section 2.5.15.
-     *
-     * @param string $subData
-     *
-     * @return array
      */
-    private function readBIFF8CellRangeAddressList($subData)
+    private function readBIFF8CellRangeAddressList(string $subData): array
     {
         $cellRangeAddresses = [];
 
@@ -7364,12 +7323,8 @@ private function readBIFF8CellRangeAddressList($subData)
     /**
      * Read BIFF5 cell range address list
      * section 2.5.15.
-     *
-     * @param string $subData
-     *
-     * @return array
      */
-    private function readBIFF5CellRangeAddressList($subData)
+    private function readBIFF5CellRangeAddressList(string $subData): array
     {
         $cellRangeAddresses = [];
 
@@ -7394,12 +7349,8 @@ private function readBIFF5CellRangeAddressList($subData)
      * Note: If there is only one sheet in the range, one gets e.g Sheet1
      * It can also happen that the REF structure uses the -1 (FFFF) code to indicate deleted sheets,
      * in which case an Exception is thrown.
-     *
-     * @param int $index
-     *
-     * @return false|string
      */
-    private function readSheetRangeByRefIndex($index)
+    private function readSheetRangeByRefIndex(int $index): string|false
     {
         if (isset($this->ref[$index])) {
             $type = $this->externalBooks[$this->ref[$index]['externalBookIndex']]['type'];
@@ -7449,10 +7400,8 @@ private function readSheetRangeByRefIndex($index)
      * section 2.5.8.
      *
      * @param string $arrayData
-     *
-     * @return array
      */
-    private static function readBIFF8ConstantArray($arrayData)
+    private static function readBIFF8ConstantArray($arrayData): array
     {
         // offset: 0; size: 1; number of columns decreased by 1
         $nc = ord($arrayData[0]);
@@ -7488,10 +7437,8 @@ private static function readBIFF8ConstantArray($arrayData)
      * returns e.g. ['value' => '5', 'size' => 9].
      *
      * @param string $valueData
-     *
-     * @return array
      */
-    private static function readBIFF8Constant($valueData)
+    private static function readBIFF8Constant($valueData): array
     {
         // offset: 0; size: 1; identifier for type of constant
         $identifier = ord($valueData[0]);
@@ -7546,10 +7493,8 @@ private static function readBIFF8Constant($valueData)
      * OpenOffice.org's Documentation of the Microsoft Excel File Format, section 2.5.4.
      *
      * @param string $rgb Encoded RGB value (4 bytes)
-     *
-     * @return array
      */
-    private static function readRGB($rgb)
+    private static function readRGB($rgb): array
     {
         // offset: 0; size 1; Red component
         $r = ord($rgb[0]);
@@ -7569,12 +7514,8 @@ private static function readRGB($rgb)
     /**
      * Read byte string (8-bit string length)
      * OpenOffice documentation: 2.5.2.
-     *
-     * @param string $subData
-     *
-     * @return array
      */
-    private function readByteStringShort($subData)
+    private function readByteStringShort(string $subData): array
     {
         // offset: 0; size: 1; length of the string (character count)
         $ln = ord($subData[0]);
@@ -7591,12 +7532,8 @@ private function readByteStringShort($subData)
     /**
      * Read byte string (16-bit string length)
      * OpenOffice documentation: 2.5.2.
-     *
-     * @param string $subData
-     *
-     * @return array
      */
-    private function readByteStringLong($subData)
+    private function readByteStringLong(string $subData): array
     {
         // offset: 0; size: 2; length of the string (character count)
         $ln = self::getUInt2d($subData, 0);
@@ -7666,10 +7603,8 @@ private static function readUnicodeStringLong($subData)
      *
      * @param string $subData
      * @param int $characterCount
-     *
-     * @return array
      */
-    private static function readUnicodeString($subData, $characterCount)
+    private static function readUnicodeString($subData, $characterCount): array
     {
         $value = '';
 
@@ -7699,10 +7634,8 @@ private static function readUnicodeString($subData, $characterCount)
      * Example:  hello"world  -->  "hello""world".
      *
      * @param string $value UTF-8 encoded string
-     *
-     * @return string
      */
-    private static function UTF8toExcelDoubleQuoted($value)
+    private static function UTF8toExcelDoubleQuoted($value): string
     {
         return '"' . str_replace('"', '""', $value) . '"';
     }
@@ -7714,7 +7647,7 @@ private static function UTF8toExcelDoubleQuoted($value)
      *
      * @return float
      */
-    private static function extractNumber($data)
+    private static function extractNumber($data): int|float
     {
         $rknumhigh = self::getInt4d($data, 4);
         $rknumlow = self::getInt4d($data, 0);
@@ -7742,7 +7675,7 @@ private static function extractNumber($data)
      *
      * @return float
      */
-    private static function getIEEE754($rknum)
+    private static function getIEEE754($rknum): float|int
     {
         if (($rknum & 0x02) != 0) {
             $value = $rknum >> 2;
@@ -7773,10 +7706,8 @@ private static function getIEEE754($rknum)
      *
      * @param string $string
      * @param bool $compressed
-     *
-     * @return string
      */
-    private static function encodeUTF16($string, $compressed = false)
+    private static function encodeUTF16($string, $compressed = false): string
     {
         if ($compressed) {
             $string = self::uncompressByteString($string);
@@ -7789,10 +7720,8 @@ private static function encodeUTF16($string, $compressed = false)
      * Convert UTF-16 string in compressed notation to uncompressed form. Only used for BIFF8.
      *
      * @param string $string
-     *
-     * @return string
      */
-    private static function uncompressByteString($string)
+    private static function uncompressByteString($string): string
     {
         $uncompressedString = '';
         $strLen = strlen($string);
@@ -7805,12 +7734,8 @@ private static function uncompressByteString($string)
 
     /**
      * Convert string to UTF-8. Only used for BIFF5.
-     *
-     * @param string $string
-     *
-     * @return string
      */
-    private function decodeCodepage($string)
+    private function decodeCodepage(string $string): string
     {
         return StringHelper::convertEncoding($string, 'UTF-8', $this->codepage);
     }
@@ -7820,10 +7745,8 @@ private function decodeCodepage($string)
      *
      * @param string $data
      * @param int $pos
-     *
-     * @return int
      */
-    public static function getUInt2d($data, $pos)
+    public static function getUInt2d($data, $pos): int
     {
         return ord($data[$pos]) | (ord($data[$pos + 1]) << 8);
     }
@@ -7846,10 +7769,8 @@ public static function getInt2d($data, $pos)
      *
      * @param string $data
      * @param int $pos
-     *
-     * @return int
      */
-    public static function getInt4d($data, $pos)
+    public static function getInt4d($data, $pos): int
     {
         // FIX: represent numbers correctly on 64-bit system
         // http://sourceforge.net/tracker/index.php?func=detail&aid=1487372&group_id=99160&atid=623334
@@ -8065,10 +7986,7 @@ private function getCFProtectionStyle(string $options, Style $style): void
     {
     }
 
-    /**
-     * @return null|float|int|string
-     */
-    private function readCFFormula(string $recordData, int $offset, int $size)
+    private function readCFFormula(string $recordData, int $offset, int $size): float|int|string|null
     {
         try {
             $formula = substr($recordData, $offset, $size);
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color.php b/src/PhpSpreadsheet/Reader/Xls/Color.php
index 06c2d0b90e..fd5d723a0f 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color.php
@@ -15,7 +15,7 @@ class Color
      *
      * @return array RGB color value, example: ['rgb' => 'FF0000']
      */
-    public static function map($color, $palette, $version)
+    public static function map($color, array $palette, $version)
     {
         if ($color <= 0x07 || $color >= 0x40) {
             // special built-in color
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
index 15d0b73313..5569bbd482 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
@@ -67,10 +67,8 @@ class BIFF5
      * Map color array from BIFF5 built-in color index.
      *
      * @param int $color
-     *
-     * @return array
      */
-    public static function lookup($color)
+    public static function lookup($color): array
     {
         return ['rgb' => self::BIFF5_COLOR_MAP[$color] ?? '000000'];
     }
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
index 019ec79e83..baa2c57fcf 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
@@ -67,10 +67,8 @@ class BIFF8
      * Map color array from BIFF8 built-in color index.
      *
      * @param int $color
-     *
-     * @return array
      */
-    public static function lookup($color)
+    public static function lookup($color): array
     {
         return ['rgb' => self::BIFF8_COLOR_MAP[$color] ?? '000000'];
     }
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php b/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
index b6a96af831..c1d34f0152 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
@@ -21,10 +21,8 @@ class BuiltIn
      * Map built-in color to RGB value.
      *
      * @param int $color Indexed color
-     *
-     * @return array
      */
-    public static function lookup($color)
+    public static function lookup($color): array
     {
         return ['rgb' => self::BUILTIN_COLOR_MAP[$color] ?? '000000'];
     }
diff --git a/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php b/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
index 0b79366b94..b33163dfa7 100644
--- a/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
+++ b/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
@@ -18,10 +18,8 @@ class ErrorCode
      * Map error code, e.g. '#N/A'.
      *
      * @param int $code
-     *
-     * @return bool|string
      */
-    public static function lookup($code)
+    public static function lookup($code): string|bool
     {
         return self::ERROR_CODE_MAP[$code] ?? false;
     }
diff --git a/src/PhpSpreadsheet/Reader/Xls/Escher.php b/src/PhpSpreadsheet/Reader/Xls/Escher.php
index e9c95c8843..8a702a6c28 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Escher.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Escher.php
@@ -553,10 +553,7 @@ private function readClientAnchor(): void
         $this->applyAttribute('setEndOffsetY', $endOffsetY);
     }
 
-    /**
-     * @param mixed $value
-     */
-    private function applyAttribute(string $name, $value): void
+    private function applyAttribute(string $name, mixed $value): void
     {
         if (method_exists($this->object, $name)) {
             $this->object->$name($value);
@@ -581,7 +578,7 @@ private function readClientData(): void
      * @param string $data Binary data
      * @param int $n Number of properties
      */
-    private function readOfficeArtRGFOPTE($data, $n): void
+    private function readOfficeArtRGFOPTE(string $data, int $n): void
     {
         $splicedComplexData = substr($data, 6 * $n);
 
diff --git a/src/PhpSpreadsheet/Reader/Xls/MD5.php b/src/PhpSpreadsheet/Reader/Xls/MD5.php
index d376c456f0..42bd92a3c7 100644
--- a/src/PhpSpreadsheet/Reader/Xls/MD5.php
+++ b/src/PhpSpreadsheet/Reader/Xls/MD5.php
@@ -24,10 +24,7 @@ class MD5
      */
     private $d;
 
-    /**
-     * @var int
-     */
-    private static $allOneBits;
+    private static int $allOneBits;
 
     /**
      * MD5 stream constructor.
@@ -51,10 +48,8 @@ public function reset(): void
 
     /**
      * Get MD5 stream context.
-     *
-     * @return string
      */
-    public function getContext()
+    public function getContext(): string
     {
         $s = '';
         foreach (['a', 'b', 'c', 'd'] as $i) {
diff --git a/src/PhpSpreadsheet/Reader/Xlsx.php b/src/PhpSpreadsheet/Reader/Xlsx.php
index c57155774a..bf36be6522 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx.php
@@ -49,10 +49,8 @@ class Xlsx extends BaseReader
 
     /**
      * ReferenceHelper instance.
-     *
-     * @var ReferenceHelper
      */
-    private $referenceHelper;
+    private ReferenceHelper $referenceHelper;
 
     /**
      * @var ZipArchive
@@ -174,12 +172,8 @@ private function loadZipNonamespace(string $filename, string $ns): SimpleXMLElem
 
     /**
      * Reads names of the worksheets from a file, without parsing the whole file to a Spreadsheet object.
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetNames($filename)
+    public function listWorksheetNames(string $filename): array
     {
         File::assertFile($filename, self::INITIAL_FILE);
 
@@ -213,12 +207,8 @@ public function listWorksheetNames($filename)
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         File::assertFile($filename, self::INITIAL_FILE);
 
@@ -362,10 +352,7 @@ private function castToFormula(?SimpleXMLElement $c, string $r, string &$cellDat
         }
     }
 
-    /**
-     * @param string $fileName
-     */
-    private function fileExistsInArchive(ZipArchive $archive, $fileName = ''): bool
+    private function fileExistsInArchive(ZipArchive $archive, string $fileName = ''): bool
     {
         // Root-relative paths
         if (strpos($fileName, '//') !== false) {
@@ -1742,12 +1729,12 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
                                             break;
                                         default:
                                             if ($mapSheetId[(int) $definedName['localSheetId']] !== null) {
-                                                $range = Worksheet::extractSheetTitle((string) $definedName, true);
+                                                $range = Worksheet::extractSheetTitle($extractedRange, true);
                                                 $scope = $excel->getSheet($mapSheetId[(int) $definedName['localSheetId']]);
                                                 if (strpos((string) $definedName, '!') !== false) {
                                                     $range[0] = str_replace("''", "'", $range[0]);
                                                     $range[0] = str_replace("'", '', $range[0]);
-                                                    if ($worksheet = $excel->getSheetByName($range[0])) { // @phpstan-ignore-line
+                                                    if ($worksheet = $excel->getSheetByName($range[0])) {
                                                         $excel->addDefinedName(DefinedName::createInstance((string) $definedName['name'], $worksheet, $extractedRange, true, $scope));
                                                     } else {
                                                         $excel->addDefinedName(DefinedName::createInstance((string) $definedName['name'], $scope, $extractedRange, true, $scope));
@@ -1760,25 +1747,24 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
                                             break;
                                     }
                                 } elseif (!isset($definedName['localSheetId'])) {
-                                    $definedRange = (string) $definedName;
                                     // "Global" definedNames
                                     $locatedSheet = null;
                                     if (strpos((string) $definedName, '!') !== false) {
                                         // Modify range, and extract the first worksheet reference
                                         // Need to split on a comma or a space if not in quotes, and extract the first part.
-                                        $definedNameValueParts = preg_split("/[ ,](?=([^']*'[^']*')*[^']*$)/miuU", $definedRange);
+                                        $definedNameValueParts = preg_split("/[ ,](?=([^']*'[^']*')*[^']*$)/miuU", $extractedRange);
                                         // Extract sheet name
                                         [$extractedSheetName] = Worksheet::extractSheetTitle((string) $definedNameValueParts[0], true); // @phpstan-ignore-line
-                                        $extractedSheetName = trim($extractedSheetName, "'");
+                                        $extractedSheetName = trim($extractedSheetName, "'"); // @phpstan-ignore-line
 
                                         // Locate sheet
                                         $locatedSheet = $excel->getSheetByName($extractedSheetName);
                                     }
 
-                                    if ($locatedSheet === null && !DefinedName::testIfFormula($definedRange)) {
-                                        $definedRange = '#REF!';
+                                    if ($locatedSheet === null && !DefinedName::testIfFormula($extractedRange)) {
+                                        $extractedRange = '#REF!';
                                     }
-                                    $excel->addDefinedName(DefinedName::createInstance((string) $definedName['name'], $locatedSheet, $definedRange, false));
+                                    $excel->addDefinedName(DefinedName::createInstance((string) $definedName['name'], $locatedSheet, $extractedRange, false));
                                 }
                             }
                         }
@@ -1853,10 +1839,7 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
         return $excel;
     }
 
-    /**
-     * @return RichText
-     */
-    private function parseRichText(?SimpleXMLElement $is)
+    private function parseRichText(?SimpleXMLElement $is): RichText
     {
         $value = new RichText();
 
@@ -1920,7 +1903,7 @@ private function parseRichText(?SimpleXMLElement $is)
                         if (isset($run->rPr->u)) {
                             $attr = $run->rPr->u->attributes();
                             if (!isset($attr['val'])) {
-                                $objFont->setUnderline(\PhpOffice\PhpSpreadsheet\Style\Font::UNDERLINE_SINGLE);
+                                $objFont->setUnderline(StyleFont::UNDERLINE_SINGLE);
                             } else {
                                 $objFont->setUnderline((string) $attr['val']);
                             }
@@ -2052,10 +2035,7 @@ private static function boolean(string $value): bool
         return $value === 'true' || $value === 'TRUE';
     }
 
-    /**
-     * @param array $hyperlinks
-     */
-    private function readHyperLinkDrawing(\PhpOffice\PhpSpreadsheet\Worksheet\Drawing $objDrawing, SimpleXMLElement $cellAnchor, $hyperlinks): void
+    private function readHyperLinkDrawing(\PhpOffice\PhpSpreadsheet\Worksheet\Drawing $objDrawing, SimpleXMLElement $cellAnchor, array $hyperlinks): void
     {
         $hlinkClick = $cellAnchor->pic->nvPicPr->cNvPr->children(Namespaces::DRAWINGML)->hlinkClick;
 
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/AutoFilter.php b/src/PhpSpreadsheet/Reader/Xlsx/AutoFilter.php
index 5cf62efd85..b1bf43b0cc 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/AutoFilter.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/AutoFilter.php
@@ -16,10 +16,7 @@ class AutoFilter
      */
     private $parent;
 
-    /**
-     * @var SimpleXMLElement
-     */
-    private $worksheetXml;
+    private SimpleXMLElement $worksheetXml;
 
     /**
      * @param Table|Worksheet $parent
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/Chart.php b/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
index c5a59f5583..789d46ee78 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/Chart.php
@@ -22,11 +22,9 @@
 
 class Chart
 {
-    /** @var string */
-    private $cNamespace;
+    private string $cNamespace;
 
-    /** @var string */
-    private $aNamespace;
+    private string $aNamespace;
 
     public function __construct(string $cNamespace = Namespaces::CHART, string $aNamespace = Namespaces::DRAWINGML)
     {
@@ -34,26 +32,42 @@ public function __construct(string $cNamespace = Namespaces::CHART, string $aNam
         $this->aNamespace = $aNamespace;
     }
 
-    /**
-     * @param string $name
-     * @param string $format
-     *
-     * @return null|bool|float|int|string
-     */
-    private static function getAttribute(SimpleXMLElement $component, $name, $format)
+    private static function getAttributeString(SimpleXMLElement $component, string $name): string|null
     {
         $attributes = $component->attributes();
         if (@isset($attributes[$name])) {
-            if ($format == 'string') {
-                return (string) $attributes[$name];
-            } elseif ($format == 'integer') {
-                return (int) $attributes[$name];
-            } elseif ($format == 'boolean') {
-                $value = (string) $attributes[$name];
-
-                return $value === 'true' || $value === '1';
-            }
+            return (string) $attributes[$name];
+        }
+
+        return null;
+    }
+
+    private static function getAttributeInteger(SimpleXMLElement $component, string $name): int|null
+    {
+        $attributes = $component->attributes();
+        if (@isset($attributes[$name])) {
+            return (int) $attributes[$name];
+        }
+
+        return null;
+    }
+
+    private static function getAttributeBoolean(SimpleXMLElement $component, string $name): bool|null
+    {
+        $attributes = $component->attributes();
+        if (@isset($attributes[$name])) {
+            $value = (string) $attributes[$name];
+
+            return $value === 'true' || $value === '1';
+        }
+
+        return null;
+    }
 
+    private static function getAttributeFloat(SimpleXMLElement $component, string $name): float|null
+    {
+        $attributes = $component->attributes();
+        if (@isset($attributes[$name])) {
             return (float) $attributes[$name];
         }
 
@@ -62,10 +76,8 @@ private static function getAttribute(SimpleXMLElement $component, $name, $format
 
     /**
      * @param string $chartName
-     *
-     * @return \PhpOffice\PhpSpreadsheet\Chart\Chart
      */
-    public function readChart(SimpleXMLElement $chartElements, $chartName)
+    public function readChart(SimpleXMLElement $chartElements, $chartName): \PhpOffice\PhpSpreadsheet\Chart\Chart
     {
         $chartElementsC = $chartElements->children($this->cNamespace);
 
@@ -103,7 +115,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                     break;
                 case 'roundedCorners':
                     /** @var bool */
-                    $roundedCorners = self::getAttribute($chartElementsC->roundedCorners, 'val', 'boolean');
+                    $roundedCorners = self::getAttributeBoolean($chartElementsC->roundedCorners, 'val');
 
                     break;
                 case 'chart':
@@ -112,14 +124,14 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                         switch ($chartDetailsKey) {
                             case 'autoTitleDeleted':
                                 /** @var bool */
-                                $autoTitleDeleted = self::getAttribute($chartElementsC->chart->autoTitleDeleted, 'val', 'boolean');
+                                $autoTitleDeleted = self::getAttributeBoolean($chartElementsC->chart->autoTitleDeleted, 'val');
 
                                 break;
                             case 'view3D':
-                                $rotX = self::getAttribute($chartDetails->rotX, 'val', 'integer');
-                                $rotY = self::getAttribute($chartDetails->rotY, 'val', 'integer');
-                                $rAngAx = self::getAttribute($chartDetails->rAngAx, 'val', 'integer');
-                                $perspective = self::getAttribute($chartDetails->perspective, 'val', 'integer');
+                                $rotX = self::getAttributeInteger($chartDetails->rotX, 'val');
+                                $rotY = self::getAttributeInteger($chartDetails->rotY, 'val');
+                                $rAngAx = self::getAttributeInteger($chartDetails->rAngAx, 'val');
+                                $perspective = self::getAttributeInteger($chartDetails->perspective, 'val');
 
                                 break;
                             case 'plotArea':
@@ -139,7 +151,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                                 foreach ($possibleNoFill->gradFill->gsLst->gs as $gradient) {
                                                     $gradient = Xlsx::testSimpleXml($gradient);
                                                     /** @var float */
-                                                    $pos = self::getAttribute($gradient, 'pos', 'float');
+                                                    $pos = self::getAttributeFloat($gradient, 'pos');
                                                     $gradientArray[] = [
                                                         $pos / ChartProperties::PERCENTAGE_MULTIPLIER,
                                                         new ChartColor($this->readColor($gradient)),
@@ -147,7 +159,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                                 }
                                             }
                                             if (isset($possibleNoFill->gradFill->lin)) {
-                                                $gradientLin = ChartProperties::XmlToAngle((string) self::getAttribute($possibleNoFill->gradFill->lin, 'ang', 'string'));
+                                                $gradientLin = ChartProperties::XmlToAngle((string) self::getAttributeString($possibleNoFill->gradFill->lin, 'ang'));
                                             }
 
                                             break;
@@ -198,7 +210,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                             $whichAxis = null;
                                             $axPos = null;
                                             if (isset($chartDetail->axPos)) {
-                                                $axPos = self::getAttribute($chartDetail->axPos, 'val', 'string');
+                                                $axPos = self::getAttributeString($chartDetail->axPos, 'val');
                                             }
                                             if ($catAxRead) {
                                                 $whichAxis = $yAxis;
@@ -269,7 +281,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                             break;
                                         case 'barChart':
                                         case 'bar3DChart':
-                                            $barDirection = self::getAttribute($chartDetail->barDir, 'val', 'string');
+                                            $barDirection = self::getAttributeString($chartDetail->barDir, 'val');
                                             $plotSer = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             $plotSer->setPlotDirection("$barDirection");
                                             $plotSeries[] = $plotSer;
@@ -291,7 +303,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                         case 'doughnutChart':
                                         case 'pieChart':
                                         case 'pie3DChart':
-                                            $explosion = self::getAttribute($chartDetail->ser->explosion, 'val', 'string');
+                                            $explosion = self::getAttributeString($chartDetail->ser->explosion, 'val');
                                             $plotSer = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             $plotSer->setPlotStyle("$explosion");
                                             $plotSeries[] = $plotSer;
@@ -300,7 +312,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                             break;
                                         case 'scatterChart':
                                             /** @var string */
-                                            $scatterStyle = self::getAttribute($chartDetail->scatterStyle, 'val', 'string');
+                                            $scatterStyle = self::getAttributeString($chartDetail->scatterStyle, 'val');
                                             $plotSer = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             $plotSer->setPlotStyle($scatterStyle);
                                             $plotSeries[] = $plotSer;
@@ -308,7 +320,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
 
                                             break;
                                         case 'bubbleChart':
-                                            $bubbleScale = self::getAttribute($chartDetail->bubbleScale, 'val', 'integer');
+                                            $bubbleScale = self::getAttributeInteger($chartDetail->bubbleScale, 'val');
                                             $plotSer = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             $plotSer->setPlotStyle("$bubbleScale");
                                             $plotSeries[] = $plotSer;
@@ -317,7 +329,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                             break;
                                         case 'radarChart':
                                             /** @var string */
-                                            $radarStyle = self::getAttribute($chartDetail->radarStyle, 'val', 'string');
+                                            $radarStyle = self::getAttributeString($chartDetail->radarStyle, 'val');
                                             $plotSer = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             $plotSer->setPlotStyle($radarStyle);
                                             $plotSeries[] = $plotSer;
@@ -326,7 +338,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                             break;
                                         case 'surfaceChart':
                                         case 'surface3DChart':
-                                            $wireFrame = self::getAttribute($chartDetail->wireframe, 'val', 'boolean');
+                                            $wireFrame = self::getAttributeBoolean($chartDetail->wireframe, 'val');
                                             $plotSer = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             $plotSer->setPlotStyle("$wireFrame");
                                             $plotSeries[] = $plotSer;
@@ -336,7 +348,7 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                         case 'stockChart':
                                             $plotSeries[] = $this->chartDataSeries($chartDetail, $chartDetailKey);
                                             if (isset($chartDetail->upDownBars->gapWidth)) {
-                                                $gapWidth = self::getAttribute($chartDetail->upDownBars->gapWidth, 'val', 'integer');
+                                                $gapWidth = self::getAttributeInteger($chartDetail->upDownBars->gapWidth, 'val');
                                             }
                                             if (isset($chartDetail->upDownBars->upBars)) {
                                                 $useUpBars = true;
@@ -372,11 +384,11 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
 
                                 break;
                             case 'plotVisOnly':
-                                $plotVisOnly = self::getAttribute($chartDetails, 'val', 'string');
+                                $plotVisOnly = self::getAttributeString($chartDetails, 'val');
 
                                 break;
                             case 'dispBlanksAs':
-                                $dispBlanksAs = self::getAttribute($chartDetails, 'val', 'string');
+                                $dispBlanksAs = self::getAttributeString($chartDetails, 'val');
 
                                 break;
                             case 'title':
@@ -395,11 +407,11 @@ public function readChart(SimpleXMLElement $chartElements, $chartName)
                                     $chartDetail = Xlsx::testSimpleXml($chartDetail);
                                     switch ($chartDetailKey) {
                                         case 'legendPos':
-                                            $legendPos = self::getAttribute($chartDetail, 'val', 'string');
+                                            $legendPos = self::getAttributeString($chartDetail, 'val');
 
                                             break;
                                         case 'overlay':
-                                            $legendOverlay = self::getAttribute($chartDetail, 'val', 'boolean');
+                                            $legendOverlay = self::getAttributeBoolean($chartDetail, 'val');
 
                                             break;
                                         case 'layout':
@@ -509,7 +521,7 @@ private function chartTitle(SimpleXMLElement $titleDetails): Title
 
                     break;
                 case 'overlay':
-                    $titleOverlay = self::getAttribute($chartDetail, 'val', 'boolean');
+                    $titleOverlay = self::getAttributeBoolean($chartDetail, 'val');
 
                     break;
                 case 'layout':
@@ -534,7 +546,7 @@ private function chartLayoutDetails(SimpleXMLElement $chartDetail): ?Layout
         $layout = [];
         foreach ($details as $detailKey => $detail) {
             $detail = Xlsx::testSimpleXml($detail);
-            $layout[$detailKey] = self::getAttribute($detail, 'val', 'string');
+            $layout[$detailKey] = self::getAttributeString($detail, 'val');
         }
 
         return new Layout($layout);
@@ -550,7 +562,7 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
         foreach ($seriesDetailSet as $seriesDetailKey => $seriesDetails) {
             switch ($seriesDetailKey) {
                 case 'grouping':
-                    $multiSeriesType = self::getAttribute($chartDetail->grouping, 'val', 'string');
+                    $multiSeriesType = self::getAttributeString($chartDetail->grouping, 'val');
 
                     break;
                 case 'ser':
@@ -570,11 +582,11 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
                         $seriesDetail = Xlsx::testSimpleXml($seriesDetail);
                         switch ($seriesKey) {
                             case 'idx':
-                                $seriesIndex = self::getAttribute($seriesDetail, 'val', 'integer');
+                                $seriesIndex = self::getAttributeInteger($seriesDetail, 'val');
 
                                 break;
                             case 'order':
-                                $seriesOrder = self::getAttribute($seriesDetail, 'val', 'integer');
+                                $seriesOrder = self::getAttributeInteger($seriesDetail, 'val');
                                 $plotOrder[$seriesIndex] = $seriesOrder;
 
                                 break;
@@ -604,7 +616,7 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
 
                                 break;
                             case 'dPt':
-                                $dptIdx = (int) self::getAttribute($seriesDetail->idx, 'val', 'string');
+                                $dptIdx = (int) self::getAttributeString($seriesDetail->idx, 'val');
                                 if (isset($seriesDetail->spPr)) {
                                     $children = $seriesDetail->spPr->children($this->aNamespace);
                                     if (isset($children->solidFill)) {
@@ -618,21 +630,21 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
                                 $trendLine = new TrendLine();
                                 $this->readLineStyle($seriesDetail, $trendLine);
                                 /** @var ?string */
-                                $trendLineType = self::getAttribute($seriesDetail->trendlineType, 'val', 'string');
+                                $trendLineType = self::getAttributeString($seriesDetail->trendlineType, 'val');
                                 /** @var ?bool */
-                                $dispRSqr = self::getAttribute($seriesDetail->dispRSqr, 'val', 'boolean');
+                                $dispRSqr = self::getAttributeBoolean($seriesDetail->dispRSqr, 'val');
                                 /** @var ?bool */
-                                $dispEq = self::getAttribute($seriesDetail->dispEq, 'val', 'boolean');
+                                $dispEq = self::getAttributeBoolean($seriesDetail->dispEq, 'val');
                                 /** @var ?int */
-                                $order = self::getAttribute($seriesDetail->order, 'val', 'integer');
+                                $order = self::getAttributeInteger($seriesDetail->order, 'val');
                                 /** @var ?int */
-                                $period = self::getAttribute($seriesDetail->period, 'val', 'integer');
+                                $period = self::getAttributeInteger($seriesDetail->period, 'val');
                                 /** @var ?float */
-                                $forward = self::getAttribute($seriesDetail->forward, 'val', 'float');
+                                $forward = self::getAttributeFloat($seriesDetail->forward, 'val');
                                 /** @var ?float */
-                                $backward = self::getAttribute($seriesDetail->backward, 'val', 'float');
+                                $backward = self::getAttributeFloat($seriesDetail->backward, 'val');
                                 /** @var ?float */
-                                $intercept = self::getAttribute($seriesDetail->intercept, 'val', 'float');
+                                $intercept = self::getAttributeFloat($seriesDetail->intercept, 'val');
                                 /** @var ?string */
                                 $name = (string) $seriesDetail->name;
                                 $trendLine->setTrendLineProperties(
@@ -650,8 +662,8 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
 
                                 break;
                             case 'marker':
-                                $marker = self::getAttribute($seriesDetail->symbol, 'val', 'string');
-                                $pointSize = self::getAttribute($seriesDetail->size, 'val', 'string');
+                                $marker = self::getAttributeString($seriesDetail->symbol, 'val');
+                                $pointSize = self::getAttributeString($seriesDetail->size, 'val');
                                 $pointSize = is_numeric($pointSize) ? ((int) $pointSize) : null;
                                 if (isset($seriesDetail->spPr)) {
                                     $children = $seriesDetail->spPr->children($this->aNamespace);
@@ -665,7 +677,7 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
 
                                 break;
                             case 'smooth':
-                                $smoothLine = self::getAttribute($seriesDetail, 'val', 'boolean');
+                                $smoothLine = self::getAttributeBoolean($seriesDetail, 'val');
 
                                 break;
                             case 'cat':
@@ -689,7 +701,7 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
 
                                 break;
                             case 'bubble3D':
-                                $bubble3D = self::getAttribute($seriesDetail, 'val', 'boolean');
+                                $bubble3D = self::getAttributeBoolean($seriesDetail, 'val');
 
                                 break;
                             case 'dLbls':
@@ -801,15 +813,13 @@ private function chartDataSeries(SimpleXMLElement $chartDetail, string $plotType
         }
         /** @phpstan-ignore-next-line */
         $series = new DataSeries($plotType, $multiSeriesType, $plotOrder, $seriesLabel, $seriesCategory, $seriesValues, $smoothLine);
+        /** @phpstan-ignore-next-line */
         $series->setPlotBubbleSizes($seriesBubbles);
 
         return $series;
     }
 
-    /**
-     * @return mixed
-     */
-    private function chartDataSeriesValueSet(SimpleXMLElement $seriesDetail, ?string $marker = null, ?ChartColor $fillColor = null, ?string $pointSize = null)
+    private function chartDataSeriesValueSet(SimpleXMLElement $seriesDetail, ?string $marker = null, ?ChartColor $fillColor = null, ?string $pointSize = null): ?DataSeriesValues
     {
         if (isset($seriesDetail->strRef)) {
             $seriesSource = (string) $seriesDetail->strRef->f;
@@ -883,7 +893,7 @@ private function chartDataSeriesValues(SimpleXMLElement $seriesValueSet, string
             $seriesValue = Xlsx::testSimpleXml($seriesValue);
             switch ($seriesValueIdx) {
                 case 'ptCount':
-                    $pointCount = self::getAttribute($seriesValue, 'val', 'integer');
+                    $pointCount = self::getAttributeInteger($seriesValue, 'val');
 
                     break;
                 case 'formatCode':
@@ -891,7 +901,7 @@ private function chartDataSeriesValues(SimpleXMLElement $seriesValueSet, string
 
                     break;
                 case 'pt':
-                    $pointVal = self::getAttribute($seriesValue, 'idx', 'integer');
+                    $pointVal = self::getAttributeInteger($seriesValue, 'idx');
                     if ($dataType == 's') {
                         $seriesVal[$pointVal] = (string) $seriesValue->v;
                     } elseif ((string) $seriesValue->v === ExcelError::NA()) {
@@ -922,7 +932,7 @@ private function chartDataSeriesValuesMultiLevel(SimpleXMLElement $seriesValueSe
                 $seriesValue = Xlsx::testSimpleXml($seriesValue);
                 switch ($seriesValueIdx) {
                     case 'ptCount':
-                        $pointCount = self::getAttribute($seriesValue, 'val', 'integer');
+                        $pointCount = self::getAttributeInteger($seriesValue, 'val');
 
                         break;
                     case 'formatCode':
@@ -930,7 +940,7 @@ private function chartDataSeriesValuesMultiLevel(SimpleXMLElement $seriesValueSe
 
                         break;
                     case 'pt':
-                        $pointVal = self::getAttribute($seriesValue, 'idx', 'integer');
+                        $pointVal = self::getAttributeInteger($seriesValue, 'idx');
                         if ($dataType == 's') {
                             $seriesVal[$pointVal][] = (string) $seriesValue->v;
                         } elseif ((string) $seriesValue->v === ExcelError::NA()) {
@@ -967,31 +977,31 @@ private function parseRichText(SimpleXMLElement $titleDetailPart): RichText
         $defaultFontColor = null;
         if (isset($titleDetailPart->pPr->defRPr)) {
             /** @var ?int */
-            $defaultFontSize = self::getAttribute($titleDetailPart->pPr->defRPr, 'sz', 'integer');
+            $defaultFontSize = self::getAttributeInteger($titleDetailPart->pPr->defRPr, 'sz');
             /** @var ?bool */
-            $defaultBold = self::getAttribute($titleDetailPart->pPr->defRPr, 'b', 'boolean');
+            $defaultBold = self::getAttributeBoolean($titleDetailPart->pPr->defRPr, 'b');
             /** @var ?bool */
-            $defaultItalic = self::getAttribute($titleDetailPart->pPr->defRPr, 'i', 'boolean');
+            $defaultItalic = self::getAttributeBoolean($titleDetailPart->pPr->defRPr, 'i');
             /** @var ?string */
-            $defaultUnderscore = self::getAttribute($titleDetailPart->pPr->defRPr, 'u', 'string');
+            $defaultUnderscore = self::getAttributeString($titleDetailPart->pPr->defRPr, 'u');
             /** @var ?string */
-            $defaultStrikethrough = self::getAttribute($titleDetailPart->pPr->defRPr, 'strike', 'string');
+            $defaultStrikethrough = self::getAttributeString($titleDetailPart->pPr->defRPr, 'strike');
             /** @var ?int */
-            $defaultBaseline = self::getAttribute($titleDetailPart->pPr->defRPr, 'baseline', 'integer');
+            $defaultBaseline = self::getAttributeInteger($titleDetailPart->pPr->defRPr, 'baseline');
             if (isset($titleDetailPart->defRPr->rFont['val'])) {
                 $defaultFontName = (string) $titleDetailPart->defRPr->rFont['val'];
             }
             if (isset($titleDetailPart->pPr->defRPr->latin)) {
                 /** @var ?string */
-                $defaultLatin = self::getAttribute($titleDetailPart->pPr->defRPr->latin, 'typeface', 'string');
+                $defaultLatin = self::getAttributeString($titleDetailPart->pPr->defRPr->latin, 'typeface');
             }
             if (isset($titleDetailPart->pPr->defRPr->ea)) {
                 /** @var ?string */
-                $defaultEastAsian = self::getAttribute($titleDetailPart->pPr->defRPr->ea, 'typeface', 'string');
+                $defaultEastAsian = self::getAttributeString($titleDetailPart->pPr->defRPr->ea, 'typeface');
             }
             if (isset($titleDetailPart->pPr->defRPr->cs)) {
                 /** @var ?string */
-                $defaultComplexScript = self::getAttribute($titleDetailPart->pPr->defRPr->cs, 'typeface', 'string');
+                $defaultComplexScript = self::getAttributeString($titleDetailPart->pPr->defRPr->cs, 'typeface');
             }
             if (isset($titleDetailPart->pPr->defRPr->solidFill)) {
                 $defaultFontColor = $this->readColor($titleDetailPart->pPr->defRPr->solidFill);
@@ -1031,18 +1041,18 @@ private function parseRichText(SimpleXMLElement $titleDetailPart): RichText
                 }
                 if (isset($titleDetailElement->rPr->latin)) {
                     /** @var ?string */
-                    $latinName = self::getAttribute($titleDetailElement->rPr->latin, 'typeface', 'string');
+                    $latinName = self::getAttributeString($titleDetailElement->rPr->latin, 'typeface');
                 }
                 if (isset($titleDetailElement->rPr->ea)) {
                     /** @var ?string */
-                    $eastAsian = self::getAttribute($titleDetailElement->rPr->ea, 'typeface', 'string');
+                    $eastAsian = self::getAttributeString($titleDetailElement->rPr->ea, 'typeface');
                 }
                 if (isset($titleDetailElement->rPr->cs)) {
                     /** @var ?string */
-                    $complexScript = self::getAttribute($titleDetailElement->rPr->cs, 'typeface', 'string');
+                    $complexScript = self::getAttributeString($titleDetailElement->rPr->cs, 'typeface');
                 }
                 /** @var ?int */
-                $fontSize = self::getAttribute($titleDetailElement->rPr, 'sz', 'integer');
+                $fontSize = self::getAttributeInteger($titleDetailElement->rPr, 'sz');
 
                 // not used now, not sure it ever was, grandfathering
                 if (isset($titleDetailElement->rPr->solidFill)) {
@@ -1050,22 +1060,22 @@ private function parseRichText(SimpleXMLElement $titleDetailPart): RichText
                 }
 
                 /** @var ?bool */
-                $bold = self::getAttribute($titleDetailElement->rPr, 'b', 'boolean');
+                $bold = self::getAttributeBoolean($titleDetailElement->rPr, 'b');
 
                 /** @var ?bool */
-                $italic = self::getAttribute($titleDetailElement->rPr, 'i', 'boolean');
+                $italic = self::getAttributeBoolean($titleDetailElement->rPr, 'i');
 
                 /** @var ?int */
-                $baseline = self::getAttribute($titleDetailElement->rPr, 'baseline', 'integer');
+                $baseline = self::getAttributeInteger($titleDetailElement->rPr, 'baseline');
 
                 /** @var ?string */
-                $underscore = self::getAttribute($titleDetailElement->rPr, 'u', 'string');
+                $underscore = self::getAttributeString($titleDetailElement->rPr, 'u');
                 if (isset($titleDetailElement->rPr->uFill->solidFill)) {
                     $underlineColor = $this->readColor($titleDetailElement->rPr->uFill->solidFill);
                 }
 
                 /** @var ?string */
-                $strikethrough = self::getAttribute($titleDetailElement->rPr, 'strike', 'string');
+                $strikethrough = self::getAttributeString($titleDetailElement->rPr, 'strike');
             }
 
             $fontFound = false;
@@ -1170,20 +1180,20 @@ private function parseFont(SimpleXMLElement $titleDetailPart): ?Font
             return null;
         }
         $fontArray = [];
-        $fontArray['size'] = self::getAttribute($titleDetailPart->pPr->defRPr, 'sz', 'integer');
-        $fontArray['bold'] = self::getAttribute($titleDetailPart->pPr->defRPr, 'b', 'boolean');
-        $fontArray['italic'] = self::getAttribute($titleDetailPart->pPr->defRPr, 'i', 'boolean');
-        $fontArray['underscore'] = self::getAttribute($titleDetailPart->pPr->defRPr, 'u', 'string');
-        $fontArray['strikethrough'] = self::getAttribute($titleDetailPart->pPr->defRPr, 'strike', 'string');
+        $fontArray['size'] = self::getAttributeInteger($titleDetailPart->pPr->defRPr, 'sz');
+        $fontArray['bold'] = self::getAttributeBoolean($titleDetailPart->pPr->defRPr, 'b');
+        $fontArray['italic'] = self::getAttributeBoolean($titleDetailPart->pPr->defRPr, 'i');
+        $fontArray['underscore'] = self::getAttributeString($titleDetailPart->pPr->defRPr, 'u');
+        $fontArray['strikethrough'] = self::getAttributeString($titleDetailPart->pPr->defRPr, 'strike');
 
         if (isset($titleDetailPart->pPr->defRPr->latin)) {
-            $fontArray['latin'] = self::getAttribute($titleDetailPart->pPr->defRPr->latin, 'typeface', 'string');
+            $fontArray['latin'] = self::getAttributeString($titleDetailPart->pPr->defRPr->latin, 'typeface');
         }
         if (isset($titleDetailPart->pPr->defRPr->ea)) {
-            $fontArray['eastAsian'] = self::getAttribute($titleDetailPart->pPr->defRPr->ea, 'typeface', 'string');
+            $fontArray['eastAsian'] = self::getAttributeString($titleDetailPart->pPr->defRPr->ea, 'typeface');
         }
         if (isset($titleDetailPart->pPr->defRPr->cs)) {
-            $fontArray['complexScript'] = self::getAttribute($titleDetailPart->pPr->defRPr->cs, 'typeface', 'string');
+            $fontArray['complexScript'] = self::getAttributeString($titleDetailPart->pPr->defRPr->cs, 'typeface');
         }
         if (isset($titleDetailPart->pPr->defRPr->solidFill)) {
             $fontArray['chartColor'] = new ChartColor($this->readColor($titleDetailPart->pPr->defRPr->solidFill));
@@ -1203,32 +1213,32 @@ private function readChartAttributes($chartDetail): array
         $plotAttributes = [];
         if (isset($chartDetail->dLbls)) {
             if (isset($chartDetail->dLbls->dLblPos)) {
-                $plotAttributes['dLblPos'] = self::getAttribute($chartDetail->dLbls->dLblPos, 'val', 'string');
+                $plotAttributes['dLblPos'] = self::getAttributeString($chartDetail->dLbls->dLblPos, 'val');
             }
             if (isset($chartDetail->dLbls->numFmt)) {
-                $plotAttributes['numFmtCode'] = self::getAttribute($chartDetail->dLbls->numFmt, 'formatCode', 'string');
-                $plotAttributes['numFmtLinked'] = self::getAttribute($chartDetail->dLbls->numFmt, 'sourceLinked', 'boolean');
+                $plotAttributes['numFmtCode'] = self::getAttributeString($chartDetail->dLbls->numFmt, 'formatCode');
+                $plotAttributes['numFmtLinked'] = self::getAttributeBoolean($chartDetail->dLbls->numFmt, 'sourceLinked');
             }
             if (isset($chartDetail->dLbls->showLegendKey)) {
-                $plotAttributes['showLegendKey'] = self::getAttribute($chartDetail->dLbls->showLegendKey, 'val', 'string');
+                $plotAttributes['showLegendKey'] = self::getAttributeString($chartDetail->dLbls->showLegendKey, 'val');
             }
             if (isset($chartDetail->dLbls->showVal)) {
-                $plotAttributes['showVal'] = self::getAttribute($chartDetail->dLbls->showVal, 'val', 'string');
+                $plotAttributes['showVal'] = self::getAttributeString($chartDetail->dLbls->showVal, 'val');
             }
             if (isset($chartDetail->dLbls->showCatName)) {
-                $plotAttributes['showCatName'] = self::getAttribute($chartDetail->dLbls->showCatName, 'val', 'string');
+                $plotAttributes['showCatName'] = self::getAttributeString($chartDetail->dLbls->showCatName, 'val');
             }
             if (isset($chartDetail->dLbls->showSerName)) {
-                $plotAttributes['showSerName'] = self::getAttribute($chartDetail->dLbls->showSerName, 'val', 'string');
+                $plotAttributes['showSerName'] = self::getAttributeString($chartDetail->dLbls->showSerName, 'val');
             }
             if (isset($chartDetail->dLbls->showPercent)) {
-                $plotAttributes['showPercent'] = self::getAttribute($chartDetail->dLbls->showPercent, 'val', 'string');
+                $plotAttributes['showPercent'] = self::getAttributeString($chartDetail->dLbls->showPercent, 'val');
             }
             if (isset($chartDetail->dLbls->showBubbleSize)) {
-                $plotAttributes['showBubbleSize'] = self::getAttribute($chartDetail->dLbls->showBubbleSize, 'val', 'string');
+                $plotAttributes['showBubbleSize'] = self::getAttributeString($chartDetail->dLbls->showBubbleSize, 'val');
             }
             if (isset($chartDetail->dLbls->showLeaderLines)) {
-                $plotAttributes['showLeaderLines'] = self::getAttribute($chartDetail->dLbls->showLeaderLines, 'val', 'string');
+                $plotAttributes['showLeaderLines'] = self::getAttributeString($chartDetail->dLbls->showLeaderLines, 'val');
             }
             if (isset($chartDetail->dLbls->spPr)) {
                 $sppr = $chartDetail->dLbls->spPr->children($this->aNamespace);
@@ -1255,10 +1265,7 @@ private function readChartAttributes($chartDetail): array
         return $plotAttributes;
     }
 
-    /**
-     * @param mixed $plotAttributes
-     */
-    private function setChartAttributes(Layout $plotArea, $plotAttributes): void
+    private function setChartAttributes(Layout $plotArea, array $plotAttributes): void
     {
         foreach ($plotAttributes as $plotAttributeKey => $plotAttributeValue) {
             switch ($plotAttributeKey) {
@@ -1308,7 +1315,7 @@ private function readEffects(SimpleXMLElement $chartDetail, ?ChartProperties $ch
             $sppr = $chartDetail;
         }
         if (isset($sppr->effectLst->glow)) {
-            $axisGlowSize = (float) self::getAttribute($sppr->effectLst->glow, 'rad', 'integer') / ChartProperties::POINTS_WIDTH_MULTIPLIER;
+            $axisGlowSize = (float) self::getAttributeInteger($sppr->effectLst->glow, 'rad') / ChartProperties::POINTS_WIDTH_MULTIPLIER;
             if ($axisGlowSize != 0.0) {
                 $colorArray = $this->readColor($sppr->effectLst->glow);
                 $chartObject->setGlowProperties($axisGlowSize, $colorArray['value'], $colorArray['alpha'], $colorArray['type']);
@@ -1317,7 +1324,7 @@ private function readEffects(SimpleXMLElement $chartDetail, ?ChartProperties $ch
 
         if (isset($sppr->effectLst->softEdge)) {
             /** @var string */
-            $softEdgeSize = self::getAttribute($sppr->effectLst->softEdge, 'rad', 'string');
+            $softEdgeSize = self::getAttributeString($sppr->effectLst->softEdge, 'rad');
             if (is_numeric($softEdgeSize)) {
                 $chartObject->setSoftEdges((float) ChartProperties::xmlToPoints($softEdgeSize));
             }
@@ -1333,19 +1340,19 @@ private function readEffects(SimpleXMLElement $chartDetail, ?ChartProperties $ch
         }
         if ($type !== '') {
             /** @var string */
-            $blur = self::getAttribute($sppr->effectLst->$type, 'blurRad', 'string');
+            $blur = self::getAttributeString($sppr->effectLst->$type, 'blurRad');
             $blur = is_numeric($blur) ? ChartProperties::xmlToPoints($blur) : null;
             /** @var string */
-            $dist = self::getAttribute($sppr->effectLst->$type, 'dist', 'string');
+            $dist = self::getAttributeString($sppr->effectLst->$type, 'dist');
             $dist = is_numeric($dist) ? ChartProperties::xmlToPoints($dist) : null;
             /** @var string */
-            $direction = self::getAttribute($sppr->effectLst->$type, 'dir', 'string');
+            $direction = self::getAttributeString($sppr->effectLst->$type, 'dir');
             $direction = is_numeric($direction) ? ChartProperties::xmlToAngle($direction) : null;
-            $algn = self::getAttribute($sppr->effectLst->$type, 'algn', 'string');
-            $rot = self::getAttribute($sppr->effectLst->$type, 'rotWithShape', 'string');
+            $algn = self::getAttributeString($sppr->effectLst->$type, 'algn');
+            $rot = self::getAttributeString($sppr->effectLst->$type, 'rotWithShape');
             $size = [];
             foreach (['sx', 'sy'] as $sizeType) {
-                $sizeValue = self::getAttribute($sppr->effectLst->$type, $sizeType, 'string');
+                $sizeValue = self::getAttributeString($sppr->effectLst->$type, $sizeType);
                 if (is_numeric($sizeValue)) {
                     $size[$sizeType] = ChartProperties::xmlToTenthOfPercent((string) $sizeValue);
                 } else {
@@ -1353,7 +1360,7 @@ private function readEffects(SimpleXMLElement $chartDetail, ?ChartProperties $ch
                 }
             }
             foreach (['kx', 'ky'] as $sizeType) {
-                $sizeValue = self::getAttribute($sppr->effectLst->$type, $sizeType, 'string');
+                $sizeValue = self::getAttributeString($sppr->effectLst->$type, $sizeType);
                 if (is_numeric($sizeValue)) {
                     $size[$sizeType] = ChartProperties::xmlToAngle((string) $sizeValue);
                 } else {
@@ -1389,17 +1396,17 @@ private function readColor(SimpleXMLElement $colorXml): array
         foreach (ChartColor::EXCEL_COLOR_TYPES as $type) {
             if (isset($colorXml->$type)) {
                 $result['type'] = $type;
-                $result['value'] = self::getAttribute($colorXml->$type, 'val', 'string');
+                $result['value'] = self::getAttributeString($colorXml->$type, 'val');
                 if (isset($colorXml->$type->alpha)) {
                     /** @var string */
-                    $alpha = self::getAttribute($colorXml->$type->alpha, 'val', 'string');
+                    $alpha = self::getAttributeString($colorXml->$type->alpha, 'val');
                     if (is_numeric($alpha)) {
                         $result['alpha'] = ChartColor::alphaFromXml($alpha);
                     }
                 }
                 if (isset($colorXml->$type->lumMod)) {
                     /** @var string */
-                    $brightness = self::getAttribute($colorXml->$type->lumMod, 'val', 'string');
+                    $brightness = self::getAttributeString($colorXml->$type->lumMod, 'val');
                     if (is_numeric($brightness)) {
                         $result['brightness'] = ChartColor::alphaFromXml($brightness);
                     }
@@ -1424,16 +1431,16 @@ private function readLineStyle(SimpleXMLElement $chartDetail, ?ChartProperties $
         }
         $lineWidth = null;
         /** @var string */
-        $lineWidthTemp = self::getAttribute($sppr->ln, 'w', 'string');
+        $lineWidthTemp = self::getAttributeString($sppr->ln, 'w');
         if (is_numeric($lineWidthTemp)) {
             $lineWidth = ChartProperties::xmlToPoints($lineWidthTemp);
         }
         /** @var string */
-        $compoundType = self::getAttribute($sppr->ln, 'cmpd', 'string');
+        $compoundType = self::getAttributeString($sppr->ln, 'cmpd');
         /** @var string */
-        $dashType = self::getAttribute($sppr->ln->prstDash, 'val', 'string');
+        $dashType = self::getAttributeString($sppr->ln->prstDash, 'val');
         /** @var string */
-        $capType = self::getAttribute($sppr->ln, 'cap', 'string');
+        $capType = self::getAttributeString($sppr->ln, 'cap');
         if (isset($sppr->ln->miter)) {
             $joinType = ChartProperties::LINE_STYLE_JOIN_MITER;
         } elseif (isset($sppr->ln->bevel)) {
@@ -1444,17 +1451,17 @@ private function readLineStyle(SimpleXMLElement $chartDetail, ?ChartProperties $
         $headArrowSize = '';
         $endArrowSize = '';
         /** @var string */
-        $headArrowType = self::getAttribute($sppr->ln->headEnd, 'type', 'string');
+        $headArrowType = self::getAttributeString($sppr->ln->headEnd, 'type');
         /** @var string */
-        $headArrowWidth = self::getAttribute($sppr->ln->headEnd, 'w', 'string');
+        $headArrowWidth = self::getAttributeString($sppr->ln->headEnd, 'w');
         /** @var string */
-        $headArrowLength = self::getAttribute($sppr->ln->headEnd, 'len', 'string');
+        $headArrowLength = self::getAttributeString($sppr->ln->headEnd, 'len');
         /** @var string */
-        $endArrowType = self::getAttribute($sppr->ln->tailEnd, 'type', 'string');
+        $endArrowType = self::getAttributeString($sppr->ln->tailEnd, 'type');
         /** @var string */
-        $endArrowWidth = self::getAttribute($sppr->ln->tailEnd, 'w', 'string');
+        $endArrowWidth = self::getAttributeString($sppr->ln->tailEnd, 'w');
         /** @var string */
-        $endArrowLength = self::getAttribute($sppr->ln->tailEnd, 'len', 'string');
+        $endArrowLength = self::getAttributeString($sppr->ln->tailEnd, 'len');
         $chartObject->setLineStyleProperties(
             $lineWidth,
             $compoundType,
@@ -1480,59 +1487,59 @@ private function setAxisProperties(SimpleXMLElement $chartDetail, ?Axis $whichAx
             return;
         }
         if (isset($chartDetail->delete)) {
-            $whichAxis->setAxisOption('hidden', (string) self::getAttribute($chartDetail->delete, 'val', 'string'));
+            $whichAxis->setAxisOption('hidden', (string) self::getAttributeString($chartDetail->delete, 'val'));
         }
         if (isset($chartDetail->numFmt)) {
             $whichAxis->setAxisNumberProperties(
-                (string) self::getAttribute($chartDetail->numFmt, 'formatCode', 'string'),
+                (string) self::getAttributeString($chartDetail->numFmt, 'formatCode'),
                 null,
-                (int) self::getAttribute($chartDetail->numFmt, 'sourceLinked', 'int')
+                (int) self::getAttributeInteger($chartDetail->numFmt, 'sourceLinked')
             );
         }
         if (isset($chartDetail->crossBetween)) {
-            $whichAxis->setCrossBetween((string) self::getAttribute($chartDetail->crossBetween, 'val', 'string'));
+            $whichAxis->setCrossBetween((string) self::getAttributeString($chartDetail->crossBetween, 'val'));
         }
         if (isset($chartDetail->majorTickMark)) {
-            $whichAxis->setAxisOption('major_tick_mark', (string) self::getAttribute($chartDetail->majorTickMark, 'val', 'string'));
+            $whichAxis->setAxisOption('major_tick_mark', (string) self::getAttributeString($chartDetail->majorTickMark, 'val'));
         }
         if (isset($chartDetail->minorTickMark)) {
-            $whichAxis->setAxisOption('minor_tick_mark', (string) self::getAttribute($chartDetail->minorTickMark, 'val', 'string'));
+            $whichAxis->setAxisOption('minor_tick_mark', (string) self::getAttributeString($chartDetail->minorTickMark, 'val'));
         }
         if (isset($chartDetail->tickLblPos)) {
-            $whichAxis->setAxisOption('axis_labels', (string) self::getAttribute($chartDetail->tickLblPos, 'val', 'string'));
+            $whichAxis->setAxisOption('axis_labels', (string) self::getAttributeString($chartDetail->tickLblPos, 'val'));
         }
         if (isset($chartDetail->crosses)) {
-            $whichAxis->setAxisOption('horizontal_crosses', (string) self::getAttribute($chartDetail->crosses, 'val', 'string'));
+            $whichAxis->setAxisOption('horizontal_crosses', (string) self::getAttributeString($chartDetail->crosses, 'val'));
         }
         if (isset($chartDetail->crossesAt)) {
-            $whichAxis->setAxisOption('horizontal_crosses_value', (string) self::getAttribute($chartDetail->crossesAt, 'val', 'string'));
+            $whichAxis->setAxisOption('horizontal_crosses_value', (string) self::getAttributeString($chartDetail->crossesAt, 'val'));
         }
         if (isset($chartDetail->scaling->orientation)) {
-            $whichAxis->setAxisOption('orientation', (string) self::getAttribute($chartDetail->scaling->orientation, 'val', 'string'));
+            $whichAxis->setAxisOption('orientation', (string) self::getAttributeString($chartDetail->scaling->orientation, 'val'));
         }
         if (isset($chartDetail->scaling->max)) {
-            $whichAxis->setAxisOption('maximum', (string) self::getAttribute($chartDetail->scaling->max, 'val', 'string'));
+            $whichAxis->setAxisOption('maximum', (string) self::getAttributeString($chartDetail->scaling->max, 'val'));
         }
         if (isset($chartDetail->scaling->min)) {
-            $whichAxis->setAxisOption('minimum', (string) self::getAttribute($chartDetail->scaling->min, 'val', 'string'));
+            $whichAxis->setAxisOption('minimum', (string) self::getAttributeString($chartDetail->scaling->min, 'val'));
         }
         if (isset($chartDetail->scaling->min)) {
-            $whichAxis->setAxisOption('minimum', (string) self::getAttribute($chartDetail->scaling->min, 'val', 'string'));
+            $whichAxis->setAxisOption('minimum', (string) self::getAttributeString($chartDetail->scaling->min, 'val'));
         }
         if (isset($chartDetail->majorUnit)) {
-            $whichAxis->setAxisOption('major_unit', (string) self::getAttribute($chartDetail->majorUnit, 'val', 'string'));
+            $whichAxis->setAxisOption('major_unit', (string) self::getAttributeString($chartDetail->majorUnit, 'val'));
         }
         if (isset($chartDetail->minorUnit)) {
-            $whichAxis->setAxisOption('minor_unit', (string) self::getAttribute($chartDetail->minorUnit, 'val', 'string'));
+            $whichAxis->setAxisOption('minor_unit', (string) self::getAttributeString($chartDetail->minorUnit, 'val'));
         }
         if (isset($chartDetail->baseTimeUnit)) {
-            $whichAxis->setAxisOption('baseTimeUnit', (string) self::getAttribute($chartDetail->baseTimeUnit, 'val', 'string'));
+            $whichAxis->setAxisOption('baseTimeUnit', (string) self::getAttributeString($chartDetail->baseTimeUnit, 'val'));
         }
         if (isset($chartDetail->majorTimeUnit)) {
-            $whichAxis->setAxisOption('majorTimeUnit', (string) self::getAttribute($chartDetail->majorTimeUnit, 'val', 'string'));
+            $whichAxis->setAxisOption('majorTimeUnit', (string) self::getAttributeString($chartDetail->majorTimeUnit, 'val'));
         }
         if (isset($chartDetail->minorTimeUnit)) {
-            $whichAxis->setAxisOption('minorTimeUnit', (string) self::getAttribute($chartDetail->minorTimeUnit, 'val', 'string'));
+            $whichAxis->setAxisOption('minorTimeUnit', (string) self::getAttributeString($chartDetail->minorTimeUnit, 'val'));
         }
         if (isset($chartDetail->txPr)) {
             $children = $chartDetail->txPr->children($this->aNamespace);
@@ -1540,7 +1547,7 @@ private function setAxisProperties(SimpleXMLElement $chartDetail, ?Axis $whichAx
             $axisText = new AxisText();
             if (isset($children->bodyPr)) {
                 /** @var string */
-                $textRotation = self::getAttribute($children->bodyPr, 'rot', 'string');
+                $textRotation = self::getAttributeString($children->bodyPr, 'rot');
                 if (is_numeric($textRotation)) {
                     $axisText->setRotation((int) ChartProperties::xmlToAngle($textRotation));
                     $addAxisText = true;
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php b/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php
index 2b14eab7cc..5368bc0173 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/ColumnAndRowAttributes.php
@@ -10,11 +10,9 @@
 
 class ColumnAndRowAttributes extends BaseParserClass
 {
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
-    /** @var ?SimpleXMLElement */
-    private $worksheetXml;
+    private ?SimpleXMLElement $worksheetXml;
 
     public function __construct(Worksheet $workSheet, ?SimpleXMLElement $worksheetXml = null)
     {
@@ -29,7 +27,7 @@ public function __construct(Worksheet $workSheet, ?SimpleXMLElement $worksheetXm
      * @param array $columnAttributes array of attributes (indexes are attribute name, values are value)
      *                               'xfIndex', 'visible', 'collapsed', 'outlineLevel', 'width', ... ?
      */
-    private function setColumnAttributes($columnAddress, array $columnAttributes): void
+    private function setColumnAttributes(string $columnAddress, array $columnAttributes): void
     {
         if (isset($columnAttributes['xfIndex'])) {
             $this->worksheet->getColumnDimension($columnAddress)->setXfIndex($columnAttributes['xfIndex']);
@@ -55,7 +53,7 @@ private function setColumnAttributes($columnAddress, array $columnAttributes): v
      * @param array $rowAttributes array of attributes (indexes are attribute name, values are value)
      *                               'xfIndex', 'visible', 'collapsed', 'outlineLevel', 'rowHeight', ... ?
      */
-    private function setRowAttributes($rowNumber, array $rowAttributes): void
+    private function setRowAttributes(int $rowNumber, array $rowAttributes): void
     {
         if (isset($rowAttributes['xfIndex'])) {
             $this->worksheet->getRowDimension($rowNumber)->setXfIndex($rowAttributes['xfIndex']);
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php b/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php
index 0a90a9d78f..5b68189e1b 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/ConditionalStyles.php
@@ -14,19 +14,16 @@
 
 class ConditionalStyles
 {
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
-    /** @var SimpleXMLElement */
-    private $worksheetXml;
+    private SimpleXMLElement $worksheetXml;
 
     /**
      * @var array
      */
     private $ns;
 
-    /** @var array */
-    private $dxfs;
+    private array $dxfs;
 
     public function __construct(Worksheet $workSheet, SimpleXMLElement $worksheetXml, array $dxfs = [])
     {
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/DataValidations.php b/src/PhpSpreadsheet/Reader/Xlsx/DataValidations.php
index 210c322f9d..d494dc9dad 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/DataValidations.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/DataValidations.php
@@ -8,11 +8,9 @@
 
 class DataValidations
 {
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
-    /** @var SimpleXMLElement */
-    private $worksheetXml;
+    private SimpleXMLElement $worksheetXml;
 
     public function __construct(Worksheet $workSheet, SimpleXMLElement $worksheetXml)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/Hyperlinks.php b/src/PhpSpreadsheet/Reader/Xlsx/Hyperlinks.php
index 7d48c7967f..e047f236ae 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/Hyperlinks.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/Hyperlinks.php
@@ -9,8 +9,7 @@
 
 class Hyperlinks
 {
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
     /** @var array */
     private $hyperlinks = [];
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/PageSetup.php b/src/PhpSpreadsheet/Reader/Xlsx/PageSetup.php
index ab57548847..ca58fbee9a 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/PageSetup.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/PageSetup.php
@@ -8,11 +8,9 @@
 
 class PageSetup extends BaseParserClass
 {
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
-    /** @var ?SimpleXMLElement */
-    private $worksheetXml;
+    private ?SimpleXMLElement $worksheetXml;
 
     public function __construct(Worksheet $workSheet, ?SimpleXMLElement $worksheetXml = null)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/Properties.php b/src/PhpSpreadsheet/Reader/Xlsx/Properties.php
index 0d4701afac..42d55415e1 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/Properties.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/Properties.php
@@ -9,11 +9,9 @@
 
 class Properties
 {
-    /** @var XmlScanner */
-    private $securityScanner;
+    private XmlScanner $securityScanner;
 
-    /** @var DocumentProperties */
-    private $docProps;
+    private DocumentProperties $docProps;
 
     public function __construct(XmlScanner $securityScanner, DocumentProperties $docProps)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/SheetViewOptions.php b/src/PhpSpreadsheet/Reader/Xlsx/SheetViewOptions.php
index 5a496444fe..1b77f0d998 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/SheetViewOptions.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/SheetViewOptions.php
@@ -7,11 +7,9 @@
 
 class SheetViewOptions extends BaseParserClass
 {
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
-    /** @var ?SimpleXMLElement */
-    private $worksheetXml;
+    private ?SimpleXMLElement $worksheetXml;
 
     public function __construct(Worksheet $workSheet, ?SimpleXMLElement $worksheetXml = null)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/SheetViews.php b/src/PhpSpreadsheet/Reader/Xlsx/SheetViews.php
index 50467fe745..98e74e3cef 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/SheetViews.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/SheetViews.php
@@ -10,14 +10,11 @@
 
 class SheetViews extends BaseParserClass
 {
-    /** @var SimpleXMLElement */
-    private $sheetViewXml;
+    private SimpleXMLElement $sheetViewXml;
 
-    /** @var SimpleXMLElement */
-    private $sheetViewAttributes;
+    private SimpleXMLElement $sheetViewAttributes;
 
-    /** @var Worksheet */
-    private $worksheet;
+    private Worksheet $worksheet;
 
     private string $activePane = '';
 
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/TableReader.php b/src/PhpSpreadsheet/Reader/Xlsx/TableReader.php
index 7f8fd85596..e434ca6836 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/TableReader.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/TableReader.php
@@ -9,15 +9,9 @@
 
 class TableReader
 {
-    /**
-     * @var Worksheet
-     */
-    private $worksheet;
+    private Worksheet $worksheet;
 
-    /**
-     * @var SimpleXMLElement
-     */
-    private $tableXml;
+    private SimpleXMLElement $tableXml;
 
     /** @var array|SimpleXMLElement */
     private $tableAttributes;
diff --git a/src/PhpSpreadsheet/Reader/Xlsx/WorkbookView.php b/src/PhpSpreadsheet/Reader/Xlsx/WorkbookView.php
index d7db6240ee..3f7a4f857f 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx/WorkbookView.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx/WorkbookView.php
@@ -7,10 +7,7 @@
 
 class WorkbookView
 {
-    /**
-     * @var Spreadsheet
-     */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     public function __construct(Spreadsheet $spreadsheet)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xml.php b/src/PhpSpreadsheet/Reader/Xml.php
index 9329ae0588..bbc14a9631 100644
--- a/src/PhpSpreadsheet/Reader/Xml.php
+++ b/src/PhpSpreadsheet/Reader/Xml.php
@@ -108,11 +108,9 @@ public function canRead(string $filename): bool
     /**
      * Check if the file is a valid SimpleXML.
      *
-     * @param string $filename
-     *
      * @return false|SimpleXMLElement
      */
-    public function trySimpleXMLLoadString($filename)
+    public function trySimpleXMLLoadString(string $filename): SimpleXMLElement|bool
     {
         try {
             $xml = simplexml_load_string(
@@ -130,12 +128,8 @@ public function trySimpleXMLLoadString($filename)
 
     /**
      * Reads names of the worksheets from a file, without parsing the whole file to a Spreadsheet object.
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetNames($filename)
+    public function listWorksheetNames(string $filename): array
     {
         File::assertFile($filename);
         if (!$this->canRead($filename)) {
@@ -160,12 +154,8 @@ public function listWorksheetNames($filename)
 
     /**
      * Return worksheet info (Name, Last Column Letter, Last Column Index, Total Rows, Total Columns).
-     *
-     * @param string $filename
-     *
-     * @return array
      */
-    public function listWorksheetInfo($filename)
+    public function listWorksheetInfo(string $filename): array
     {
         File::assertFile($filename);
         if (!$this->canRead($filename)) {
diff --git a/src/PhpSpreadsheet/Reader/Xml/PageSettings.php b/src/PhpSpreadsheet/Reader/Xml/PageSettings.php
index 137cabaf30..d3b4ccc09c 100644
--- a/src/PhpSpreadsheet/Reader/Xml/PageSettings.php
+++ b/src/PhpSpreadsheet/Reader/Xml/PageSettings.php
@@ -10,10 +10,7 @@
 
 class PageSettings
 {
-    /**
-     * @var stdClass
-     */
-    private $printSettings;
+    private stdClass $printSettings;
 
     public function __construct(SimpleXMLElement $xmlX)
     {
diff --git a/src/PhpSpreadsheet/Reader/Xml/Properties.php b/src/PhpSpreadsheet/Reader/Xml/Properties.php
index e216c254da..17e1121306 100644
--- a/src/PhpSpreadsheet/Reader/Xml/Properties.php
+++ b/src/PhpSpreadsheet/Reader/Xml/Properties.php
@@ -8,10 +8,7 @@
 
 class Properties
 {
-    /**
-     * @var Spreadsheet
-     */
-    protected $spreadsheet;
+    protected Spreadsheet $spreadsheet;
 
     public function __construct(Spreadsheet $spreadsheet)
     {
diff --git a/src/PhpSpreadsheet/ReferenceHelper.php b/src/PhpSpreadsheet/ReferenceHelper.php
index 4c7de199ee..abd3addf8d 100644
--- a/src/PhpSpreadsheet/ReferenceHelper.php
+++ b/src/PhpSpreadsheet/ReferenceHelper.php
@@ -59,10 +59,8 @@ protected function __construct()
      *
      * @param string $a First column to test (e.g. 'AA')
      * @param string $b Second column to test (e.g. 'Z')
-     *
-     * @return int
      */
-    public static function columnSort($a, $b)
+    public static function columnSort(string $a, string $b): int
     {
         return strcasecmp(strlen($a) . $a, strlen($b) . $b);
     }
@@ -73,10 +71,8 @@ public static function columnSort($a, $b)
      *
      * @param string $a First column to test (e.g. 'AA')
      * @param string $b Second column to test (e.g. 'Z')
-     *
-     * @return int
      */
-    public static function columnReverseSort(string $a, string $b)
+    public static function columnReverseSort(string $a, string $b): int
     {
         return -strcasecmp(strlen($a) . $a, strlen($b) . $b);
     }
@@ -87,10 +83,8 @@ public static function columnReverseSort(string $a, string $b)
      *
      * @param string $a First cell to test (e.g. 'AA1')
      * @param string $b Second cell to test (e.g. 'Z1')
-     *
-     * @return int
      */
-    public static function cellSort(string $a, string $b)
+    public static function cellSort(string $a, string $b): int
     {
         /** @scrutinizer be-damned */
         sscanf($a, '%[A-Z]%d', $ac, $ar);
@@ -113,10 +107,8 @@ public static function cellSort(string $a, string $b)
      *
      * @param string $a First cell to test (e.g. 'AA1')
      * @param string $b Second cell to test (e.g. 'Z1')
-     *
-     * @return int
      */
-    public static function cellReverseSort(string $a, string $b)
+    public static function cellReverseSort(string $a, string $b): int
     {
         /** @scrutinizer be-damned */
         sscanf($a, '%[A-Z]%d', $ac, $ar);
@@ -409,10 +401,10 @@ public function insertNewBefore(
         // Find missing coordinates. This is important when inserting column before the last column
         $cellCollection = $worksheet->getCellCollection();
         $missingCoordinates = array_filter(
-            array_map(function ($row) use ($highestColumn) {
+            array_map(function ($row) use ($highestColumn): string {
                 return "{$highestColumn}{$row}";
             }, range(1, $highestRow)),
-            function ($coordinate) use ($cellCollection) {
+            function ($coordinate) use ($cellCollection): bool {
                 return $cellCollection->has($coordinate) === false;
             }
         );
@@ -575,7 +567,7 @@ public function updateFormulaReferences(
         $worksheetName = '',
         bool $includeAbsoluteReferences = false,
         bool $onlyAbsoluteReferences = false
-    ) {
+    ): string {
         if (
             $this->cellReferenceHelper === null ||
             $this->cellReferenceHelper->refreshRequired($beforeCellAddress, $numberOfColumns, $numberOfRows)
@@ -881,7 +873,7 @@ private function updateCellReference($cellReference = 'A1', bool $includeAbsolut
      * @param string $oldName Old name (name to replace)
      * @param string $newName New name
      */
-    public function updateNamedFormulae(Spreadsheet $spreadsheet, $oldName = '', $newName = ''): void
+    public function updateNamedFormulae(Spreadsheet $spreadsheet, string $oldName = '', string $newName = ''): void
     {
         if ($oldName == '') {
             return;
diff --git a/src/PhpSpreadsheet/RichText/ITextElement.php b/src/PhpSpreadsheet/RichText/ITextElement.php
index 39b70c868b..284a365e35 100644
--- a/src/PhpSpreadsheet/RichText/ITextElement.php
+++ b/src/PhpSpreadsheet/RichText/ITextElement.php
@@ -2,6 +2,8 @@
 
 namespace PhpOffice\PhpSpreadsheet\RichText;
 
+use PhpOffice\PhpSpreadsheet\Style\Font;
+
 interface ITextElement
 {
     /**
@@ -23,7 +25,7 @@ public function setText($text);
     /**
      * Get font.
      *
-     * @return null|\PhpOffice\PhpSpreadsheet\Style\Font
+     * @return null|Font
      */
     public function getFont();
 
diff --git a/src/PhpSpreadsheet/RichText/RichText.php b/src/PhpSpreadsheet/RichText/RichText.php
index 88e7c79236..564b0fe44f 100644
--- a/src/PhpSpreadsheet/RichText/RichText.php
+++ b/src/PhpSpreadsheet/RichText/RichText.php
@@ -13,7 +13,7 @@ class RichText implements IComparable
      *
      * @var ITextElement[]
      */
-    private $richTextElements;
+    private array $richTextElements;
 
     /**
      * Create a new RichText instance.
@@ -44,7 +44,7 @@ public function __construct(?Cell $cell = null)
      *
      * @return $this
      */
-    public function addText(ITextElement $text)
+    public function addText(ITextElement $text): static
     {
         $this->richTextElements[] = $text;
 
@@ -55,10 +55,8 @@ public function addText(ITextElement $text)
      * Create text.
      *
      * @param string $text Text
-     *
-     * @return TextElement
      */
-    public function createText($text)
+    public function createText($text): TextElement
     {
         $objText = new TextElement($text);
         $this->addText($objText);
@@ -70,10 +68,8 @@ public function createText($text)
      * Create text run.
      *
      * @param string $text Text
-     *
-     * @return Run
      */
-    public function createTextRun($text)
+    public function createTextRun($text): Run
     {
         $objText = new Run($text);
         $this->addText($objText);
@@ -83,10 +79,8 @@ public function createTextRun($text)
 
     /**
      * Get plain text.
-     *
-     * @return string
      */
-    public function getPlainText()
+    public function getPlainText(): string
     {
         // Return value
         $returnValue = '';
@@ -101,10 +95,8 @@ public function getPlainText()
 
     /**
      * Convert to string.
-     *
-     * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         return $this->getPlainText();
     }
@@ -126,7 +118,7 @@ public function getRichTextElements()
      *
      * @return $this
      */
-    public function setRichTextElements(array $textElements)
+    public function setRichTextElements(array $textElements): static
     {
         $this->richTextElements = $textElements;
 
@@ -138,7 +130,7 @@ public function setRichTextElements(array $textElements)
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         $hashElements = '';
         foreach ($this->richTextElements as $element) {
diff --git a/src/PhpSpreadsheet/RichText/Run.php b/src/PhpSpreadsheet/RichText/Run.php
index 862cdbf92b..ebc1865805 100644
--- a/src/PhpSpreadsheet/RichText/Run.php
+++ b/src/PhpSpreadsheet/RichText/Run.php
@@ -28,7 +28,7 @@ public function __construct($text = '')
     /**
      * Get font.
      *
-     * @return null|\PhpOffice\PhpSpreadsheet\Style\Font
+     * @return null|Font
      */
     public function getFont()
     {
@@ -42,7 +42,7 @@ public function getFont()
      *
      * @return $this
      */
-    public function setFont(?Font $font = null)
+    public function setFont(?Font $font = null): static
     {
         $this->font = $font;
 
@@ -54,7 +54,7 @@ public function setFont(?Font $font = null)
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->getText() .
diff --git a/src/PhpSpreadsheet/RichText/TextElement.php b/src/PhpSpreadsheet/RichText/TextElement.php
index ee693a2b3f..bd30d6276b 100644
--- a/src/PhpSpreadsheet/RichText/TextElement.php
+++ b/src/PhpSpreadsheet/RichText/TextElement.php
@@ -2,6 +2,8 @@
 
 namespace PhpOffice\PhpSpreadsheet\RichText;
 
+use PhpOffice\PhpSpreadsheet\Style\Font;
+
 class TextElement implements ITextElement
 {
     /**
@@ -49,7 +51,7 @@ public function setText($text)
     /**
      * Get font. For this class, the return value is always null.
      *
-     * @return null|\PhpOffice\PhpSpreadsheet\Style\Font
+     * @return null|Font
      */
     public function getFont()
     {
diff --git a/src/PhpSpreadsheet/Settings.php b/src/PhpSpreadsheet/Settings.php
index 214865afdf..d286afc685 100644
--- a/src/PhpSpreadsheet/Settings.php
+++ b/src/PhpSpreadsheet/Settings.php
@@ -53,7 +53,7 @@ class Settings
      *
      * @return bool Success or failure
      */
-    public static function setLocale(string $locale)
+    public static function setLocale(string $locale): bool
     {
         return Calculation::getInstance()->setLocale($locale);
     }
@@ -91,7 +91,7 @@ public static function getChartRenderer(): ?string
 
     public static function htmlEntityFlags(): int
     {
-        return \ENT_COMPAT;
+        return ENT_COMPAT;
     }
 
     /**
diff --git a/src/PhpSpreadsheet/Shared/Date.php b/src/PhpSpreadsheet/Shared/Date.php
index 9f5abe34d9..700ee3c24f 100644
--- a/src/PhpSpreadsheet/Shared/Date.php
+++ b/src/PhpSpreadsheet/Shared/Date.php
@@ -72,7 +72,7 @@ class Date
      *
      * @return bool Success or failure
      */
-    public static function setExcelCalendar($baseYear)
+    public static function setExcelCalendar($baseYear): bool
     {
         if (
             ($baseYear == self::CALENDAR_WINDOWS_1900) ||
@@ -103,7 +103,7 @@ public static function getExcelCalendar()
      *
      * @return bool Success or failure
      */
-    public static function setDefaultTimezone($timeZone)
+    public static function setDefaultTimezone($timeZone): bool
     {
         try {
             $timeZone = self::validateTimeZone($timeZone);
@@ -147,7 +147,7 @@ public static function getDefaultTimezoneOrNull(): ?DateTimeZone
      *
      * @return ?DateTimeZone The timezone as a timezone object
      */
-    private static function validateTimeZone($timeZone)
+    private static function validateTimeZone($timeZone): ?DateTimeZone
     {
         if ($timeZone instanceof DateTimeZone || $timeZone === null) {
             return $timeZone;
@@ -252,7 +252,7 @@ public static function excelToDateTimeObject($excelTimestamp, $timeZone = null)
      *
      * @return int Unix timetamp for this date/time
      */
-    public static function excelToTimestamp($excelTimestamp, $timeZone = null)
+    public static function excelToTimestamp($excelTimestamp, $timeZone = null): int
     {
         $dto = self::excelToDateTimeObject($excelTimestamp, $timeZone);
         self::roundMicroseconds($dto);
@@ -289,7 +289,7 @@ public static function PHPToExcel($dateValue)
      *
      * @return float MS Excel serialized date/time value
      */
-    public static function dateTimeToExcel(DateTimeInterface $dateValue)
+    public static function dateTimeToExcel(DateTimeInterface $dateValue): float
     {
         $seconds = (float) sprintf('%d.%06d', $dateValue->format('s'), $dateValue->format('u'));
 
@@ -312,7 +312,7 @@ public static function dateTimeToExcel(DateTimeInterface $dateValue)
      *
      * @return false|float MS Excel serialized date/time value
      */
-    public static function timestampToExcel($unixTimestamp)
+    public static function timestampToExcel($unixTimestamp): bool|float
     {
         if (!is_numeric($unixTimestamp)) {
             return false;
@@ -333,7 +333,7 @@ public static function timestampToExcel($unixTimestamp)
      *
      * @return float Excel date/time value
      */
-    public static function formattedPHPToExcel($year, $month, $day, $hours = 0, $minutes = 0, $seconds = 0)
+    public static function formattedPHPToExcel($year, $month, $day, $hours = 0, $minutes = 0, $seconds = 0): float
     {
         if (self::$excelCalendar == self::CALENDAR_WINDOWS_1900) {
             //
@@ -372,10 +372,8 @@ public static function formattedPHPToExcel($year, $month, $day, $hours = 0, $min
      * Is a given cell a date/time?
      *
      * @param mixed $value
-     *
-     * @return bool
      */
-    public static function isDateTime(Cell $cell, $value = null, bool $dateWithoutTimeOkay = true)
+    public static function isDateTime(Cell $cell, $value = null, bool $dateWithoutTimeOkay = true): bool
     {
         $result = false;
         $worksheet = $cell->getWorksheetOrNull();
@@ -404,10 +402,8 @@ public static function isDateTime(Cell $cell, $value = null, bool $dateWithoutTi
 
     /**
      * Is a given NumberFormat code a date/time format code?
-     *
-     * @return bool
      */
-    public static function isDateTimeFormat(NumberFormat $excelFormatCode, bool $dateWithoutTimeOkay = true)
+    public static function isDateTimeFormat(NumberFormat $excelFormatCode, bool $dateWithoutTimeOkay = true): bool
     {
         return self::isDateTimeFormatCode((string) $excelFormatCode->getFormatCode(), $dateWithoutTimeOkay);
     }
@@ -419,10 +415,8 @@ public static function isDateTimeFormat(NumberFormat $excelFormatCode, bool $dat
      * Is a given number format code a date/time?
      *
      * @param string $excelFormatCode
-     *
-     * @return bool
      */
-    public static function isDateTimeFormatCode($excelFormatCode, bool $dateWithoutTimeOkay = true)
+    public static function isDateTimeFormatCode($excelFormatCode, bool $dateWithoutTimeOkay = true): bool
     {
         if (strtolower($excelFormatCode) === strtolower(NumberFormat::FORMAT_GENERAL)) {
             //    "General" contains an epoch letter 'e', so we trap for it explicitly here (case-insensitive check)
@@ -482,7 +476,7 @@ public static function isDateTimeFormatCode($excelFormatCode, bool $dateWithoutT
      *
      * @return false|float Excel date/time serial value
      */
-    public static function stringToExcel($dateValue)
+    public static function stringToExcel($dateValue): bool|float
     {
         if (strlen($dateValue) < 2) {
             return false;
diff --git a/src/PhpSpreadsheet/Shared/Drawing.php b/src/PhpSpreadsheet/Shared/Drawing.php
index f69310fc61..edaad86153 100644
--- a/src/PhpSpreadsheet/Shared/Drawing.php
+++ b/src/PhpSpreadsheet/Shared/Drawing.php
@@ -15,7 +15,7 @@ class Drawing
      *
      * @return int Value in EMU
      */
-    public static function pixelsToEMU($pixelValue)
+    public static function pixelsToEMU($pixelValue): int|float
     {
         return $pixelValue * 9525;
     }
@@ -27,7 +27,7 @@ public static function pixelsToEMU($pixelValue)
      *
      * @return int Value in pixels
      */
-    public static function EMUToPixels($emuValue)
+    public static function EMUToPixels($emuValue): int
     {
         $emuValue = (int) $emuValue;
         if ($emuValue != 0) {
@@ -46,7 +46,7 @@ public static function EMUToPixels($emuValue)
      *
      * @return float|int Value in cell dimension
      */
-    public static function pixelsToCellDimension($pixelValue, \PhpOffice\PhpSpreadsheet\Style\Font $defaultFont)
+    public static function pixelsToCellDimension($pixelValue, \PhpOffice\PhpSpreadsheet\Style\Font $defaultFont): int|float
     {
         // Font name and size
         $name = $defaultFont->getName();
@@ -72,7 +72,7 @@ public static function pixelsToCellDimension($pixelValue, \PhpOffice\PhpSpreadsh
      *
      * @return int Value in pixels
      */
-    public static function cellDimensionToPixels($cellWidth, \PhpOffice\PhpSpreadsheet\Style\Font $defaultFont)
+    public static function cellDimensionToPixels($cellWidth, \PhpOffice\PhpSpreadsheet\Style\Font $defaultFont): int
     {
         // Font name and size
         $name = $defaultFont->getName();
@@ -102,7 +102,7 @@ public static function cellDimensionToPixels($cellWidth, \PhpOffice\PhpSpreadshe
      *
      * @return float Value in points
      */
-    public static function pixelsToPoints($pixelValue)
+    public static function pixelsToPoints($pixelValue): float
     {
         return $pixelValue * 0.75;
     }
@@ -114,7 +114,7 @@ public static function pixelsToPoints($pixelValue)
      *
      * @return int Value in pixels
      */
-    public static function pointsToPixels($pointValue)
+    public static function pointsToPixels($pointValue): int
     {
         if ($pointValue != 0) {
             return (int) ceil($pointValue / 0.75);
@@ -130,7 +130,7 @@ public static function pointsToPixels($pointValue)
      *
      * @return int Angle
      */
-    public static function degreesToAngle($degrees)
+    public static function degreesToAngle($degrees): int
     {
         return (int) round($degrees * 60000);
     }
@@ -142,7 +142,7 @@ public static function degreesToAngle($degrees)
      *
      * @return int Degrees
      */
-    public static function angleToDegrees($angle)
+    public static function angleToDegrees($angle): int
     {
         $angle = (int) $angle;
         if ($angle != 0) {
@@ -159,13 +159,11 @@ public static function angleToDegrees($angle)
      *
      * @param string $bmpFilename Path to Windows DIB (BMP) image
      *
-     * @return GdImage|resource
-     *
      * @deprecated 1.26 use Php function imagecreatefrombmp instead
      *
      * @codeCoverageIgnore
      */
-    public static function imagecreatefrombmp($bmpFilename)
+    public static function imagecreatefrombmp($bmpFilename): GdImage
     {
         $retVal = @imagecreatefrombmp($bmpFilename);
         if ($retVal === false) {
diff --git a/src/PhpSpreadsheet/Shared/Escher/DgContainer.php b/src/PhpSpreadsheet/Shared/Escher/DgContainer.php
index 51c6860cbe..9cf5d43b5c 100644
--- a/src/PhpSpreadsheet/Shared/Escher/DgContainer.php
+++ b/src/PhpSpreadsheet/Shared/Escher/DgContainer.php
@@ -3,25 +3,21 @@
 namespace PhpOffice\PhpSpreadsheet\Shared\Escher;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
+use PhpOffice\PhpSpreadsheet\Shared\Escher\DgContainer\SpgrContainer;
 
 class DgContainer
 {
     /**
      * Drawing index, 1-based.
-     *
-     * @var ?int
      */
-    private $dgId;
+    private ?int $dgId = null;
 
     /**
      * Last shape index in this drawing.
-     *
-     * @var ?int
      */
-    private $lastSpId;
+    private ?int $lastSpId = null;
 
-    /** @var ?DgContainer\SpgrContainer */
-    private $spgrContainer;
+    private ?SpgrContainer $spgrContainer = null;
 
     public function getDgId(): ?int
     {
diff --git a/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer.php b/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer.php
index 260df9cd4c..76fe47608d 100644
--- a/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer.php
+++ b/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer.php
@@ -6,10 +6,8 @@ class SpgrContainer
 {
     /**
      * Parent Shape Group Container.
-     *
-     * @var null|SpgrContainer
      */
-    private $parent;
+    private ?self $parent = null;
 
     /**
      * Shape Container collection.
@@ -58,7 +56,7 @@ public function getChildren(): array
      *
      * @return SpgrContainer\SpContainer[]
      */
-    public function getAllSpContainers()
+    public function getAllSpContainers(): array
     {
         $allSpContainers = [];
 
diff --git a/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer/SpContainer.php b/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer/SpContainer.php
index 8a81ff5797..426d775ed7 100644
--- a/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer/SpContainer.php
+++ b/src/PhpSpreadsheet/Shared/Escher/DgContainer/SpgrContainer/SpContainer.php
@@ -354,7 +354,7 @@ public function getEndOffsetY()
      *
      * @return int Nesting level
      */
-    public function getNestingLevel()
+    public function getNestingLevel(): int
     {
         $nestingLevel = 0;
 
diff --git a/src/PhpSpreadsheet/Shared/Escher/DggContainer/BstoreContainer/BSE/Blip.php b/src/PhpSpreadsheet/Shared/Escher/DggContainer/BstoreContainer/BSE/Blip.php
index 03b261f8fe..ea036afff2 100644
--- a/src/PhpSpreadsheet/Shared/Escher/DggContainer/BstoreContainer/BSE/Blip.php
+++ b/src/PhpSpreadsheet/Shared/Escher/DggContainer/BstoreContainer/BSE/Blip.php
@@ -8,10 +8,8 @@ class Blip
 {
     /**
      * The parent BSE.
-     *
-     * @var BSE
      */
-    private $parent;
+    private BSE $parent;
 
     /**
      * Raw image data.
diff --git a/src/PhpSpreadsheet/Shared/Font.php b/src/PhpSpreadsheet/Shared/Font.php
index b868aaa23d..1bcab29144 100644
--- a/src/PhpSpreadsheet/Shared/Font.php
+++ b/src/PhpSpreadsheet/Shared/Font.php
@@ -296,7 +296,7 @@ public static function getExtraFontArray(): array
      *
      * @return bool Success or failure
      */
-    public static function setAutoSizeMethod($method)
+    public static function setAutoSizeMethod($method): bool
     {
         if (!in_array($method, self::AUTOSIZE_METHODS)) {
             return false;
@@ -470,12 +470,11 @@ public static function getTextWidthPixelsExact(string $text, FontStyle $font, in
     /**
      * Get approximate width in pixels for a string of text in a certain font at a certain rotation angle.
      *
-     * @param string $columnText
      * @param int $rotation
      *
      * @return int Text width in pixels (no padding added)
      */
-    public static function getTextWidthPixelsApprox($columnText, FontStyle $font, $rotation = 0)
+    public static function getTextWidthPixelsApprox(string $columnText, FontStyle $font, $rotation = 0): int
     {
         $fontName = $font->getName();
         $fontSize = $font->getSize();
@@ -528,7 +527,7 @@ public static function getTextWidthPixelsApprox($columnText, FontStyle $font, $r
      *
      * @return int Font size (in pixels)
      */
-    public static function fontSizeToPixels($fontSizeInPoints)
+    public static function fontSizeToPixels($fontSizeInPoints): int
     {
         return (int) ((4 / 3) * $fontSizeInPoints);
     }
@@ -540,7 +539,7 @@ public static function fontSizeToPixels($fontSizeInPoints)
      *
      * @return int Size (in pixels)
      */
-    public static function inchSizeToPixels($sizeInInch)
+    public static function inchSizeToPixels($sizeInInch): int|float
     {
         return $sizeInInch * 96;
     }
@@ -552,7 +551,7 @@ public static function inchSizeToPixels($sizeInInch)
      *
      * @return float Size (in pixels)
      */
-    public static function centimeterSizeToPixels($sizeInCm)
+    public static function centimeterSizeToPixels($sizeInCm): float
     {
         return $sizeInCm * 37.795275591;
     }
@@ -639,7 +638,7 @@ public static function getTrueTypeFontFileFromFont(FontStyle $font, bool $checkP
      *
      * @return int Character set code
      */
-    public static function getCharsetFromFontName($fontName)
+    public static function getCharsetFromFontName($fontName): int
     {
         return self::CHARSET_FROM_FONT_NAME[$fontName] ?? self::CHARSET_ANSI_LATIN;
     }
@@ -651,9 +650,9 @@ public static function getCharsetFromFontName($fontName)
      * @param FontStyle $font The workbooks default font
      * @param bool $returnAsPixels true = return column width in pixels, false = return in OOXML units
      *
-     * @return mixed Column width
+     * @return ($returnAsPixels is true ? int : float) Column width
      */
-    public static function getDefaultColumnWidthByFont(FontStyle $font, $returnAsPixels = false)
+    public static function getDefaultColumnWidthByFont(FontStyle $font, bool $returnAsPixels = false): float|int
     {
         if (isset(self::DEFAULT_COLUMN_WIDTHS[$font->getName()][$font->getSize()])) {
             // Exact width can be determined
@@ -685,7 +684,7 @@ public static function getDefaultColumnWidthByFont(FontStyle $font, $returnAsPix
      *
      * @return float Row height in points
      */
-    public static function getDefaultRowHeightByFont(FontStyle $font)
+    public static function getDefaultRowHeightByFont(FontStyle $font): float
     {
         $name = $font->getName();
         $size = $font->getSize();
diff --git a/src/PhpSpreadsheet/Shared/OLE.php b/src/PhpSpreadsheet/Shared/OLE.php
index c14afb2cd0..7ea538b8b1 100644
--- a/src/PhpSpreadsheet/Shared/OLE.php
+++ b/src/PhpSpreadsheet/Shared/OLE.php
@@ -114,7 +114,7 @@ class OLE
      *
      * @return bool true on success, PEAR_Error on failure
      */
-    public function read($filename)
+    public function read($filename): bool
     {
         $fh = @fopen($filename, 'rb');
         if ($fh === false) {
@@ -200,10 +200,8 @@ public function read($filename)
 
     /**
      * @param int $blockId byte offset from beginning of file
-     *
-     * @return int
      */
-    public function getBlockOffset($blockId)
+    public function getBlockOffset(int $blockId): int
     {
         return 512 + $blockId * $this->bigBlockSize;
     }
@@ -304,7 +302,7 @@ private static function readInt4($fileHandle)
      *
      * @return bool true on success, PEAR_Error on failure
      */
-    public function readPpsWks($blockId)
+    public function readPpsWks($blockId): bool
     {
         $fh = $this->getStream($blockId);
         for ($pos = 0; true; $pos += 128) {
@@ -381,7 +379,7 @@ public function readPpsWks($blockId)
      *
      * @return bool Whether the PPS tree for the given PPS is complete
      */
-    private function ppsTreeComplete($index)
+    private function ppsTreeComplete($index): bool
     {
         return isset($this->_list[$index]) &&
             ($pps = $this->_list[$index]) &&
@@ -401,7 +399,7 @@ private function ppsTreeComplete($index)
      *
      * @return bool true if it's a File PPS, false otherwise
      */
-    public function isFile($index)
+    public function isFile($index): bool
     {
         if (isset($this->_list[$index])) {
             return $this->_list[$index]->Type == self::OLE_PPS_TYPE_FILE;
@@ -418,7 +416,7 @@ public function isFile($index)
      *
      * @return bool true if it's a Root PPS, false otherwise
      */
-    public function isRoot($index)
+    public function isRoot($index): bool
     {
         if (isset($this->_list[$index])) {
             return $this->_list[$index]->Type == self::OLE_PPS_TYPE_ROOT;
@@ -432,7 +430,7 @@ public function isRoot($index)
      *
      * @return int The total number of PPS's found in the OLE container
      */
-    public function ppsTotal()
+    public function ppsTotal(): int
     {
         return count($this->_list);
     }
@@ -450,7 +448,7 @@ public function ppsTotal()
      *
      * @see OLE_PPS_File::getStream()
      */
-    public function getData($index, $position, $length)
+    public function getData($index, $position, $length): string
     {
         // if position is not valid return empty string
         if (!isset($this->_list[$index]) || ($position >= $this->_list[$index]->Size) || ($position < 0)) {
@@ -487,7 +485,7 @@ public function getDataLength($index)
      *
      * @return string The string in Unicode
      */
-    public static function ascToUcs($ascii)
+    public static function ascToUcs($ascii): string
     {
         $rawname = '';
         $iMax = strlen($ascii);
@@ -507,7 +505,7 @@ public static function ascToUcs($ascii)
      *
      * @return string The string for the OLE container
      */
-    public static function localDateToOLE($date)
+    public static function localDateToOLE($date): string
     {
         if (!$date) {
             return "\x00\x00\x00\x00\x00\x00\x00\x00";
diff --git a/src/PhpSpreadsheet/Shared/OLE/ChainedBlockStream.php b/src/PhpSpreadsheet/Shared/OLE/ChainedBlockStream.php
index 5d5babc3f4..28c72302f3 100644
--- a/src/PhpSpreadsheet/Shared/OLE/ChainedBlockStream.php
+++ b/src/PhpSpreadsheet/Shared/OLE/ChainedBlockStream.php
@@ -49,7 +49,7 @@ class ChainedBlockStream
      *
      * @return bool true on success
      */
-    public function stream_open($path, $mode, $options, &$openedPath) // @codingStandardsIgnoreLine
+    public function stream_open($path, $mode, $options, &$openedPath): bool // @codingStandardsIgnoreLine
     {
         if ($mode[0] !== 'r') {
             if ($options & STREAM_REPORT_ERRORS) {
@@ -117,7 +117,7 @@ public function stream_close(): void // @codingStandardsIgnoreLine
      *
      * @return false|string
      */
-    public function stream_read($count) // @codingStandardsIgnoreLine
+    public function stream_read($count): bool|string // @codingStandardsIgnoreLine
     {
         if ($this->stream_eof()) {
             return false;
@@ -133,7 +133,7 @@ public function stream_read($count) // @codingStandardsIgnoreLine
      *
      * @return bool TRUE if the file pointer is at EOF; otherwise FALSE
      */
-    public function stream_eof() // @codingStandardsIgnoreLine
+    public function stream_eof(): bool // @codingStandardsIgnoreLine
     {
         return $this->pos >= strlen($this->data);
     }
@@ -154,10 +154,8 @@ public function stream_tell() // @codingStandardsIgnoreLine
      *
      * @param int $offset byte offset
      * @param int $whence SEEK_SET, SEEK_CUR or SEEK_END
-     *
-     * @return bool
      */
-    public function stream_seek($offset, $whence) // @codingStandardsIgnoreLine
+    public function stream_seek($offset, $whence): bool // @codingStandardsIgnoreLine
     {
         if ($whence == SEEK_SET && $offset >= 0) {
             $this->pos = $offset;
@@ -176,10 +174,8 @@ public function stream_seek($offset, $whence) // @codingStandardsIgnoreLine
     /**
      * Implements support for fstat(). Currently the only supported field is
      * "size".
-     *
-     * @return array
      */
-    public function stream_stat() // @codingStandardsIgnoreLine
+    public function stream_stat(): array // @codingStandardsIgnoreLine
     {
         return [
             'size' => strlen($this->data),
diff --git a/src/PhpSpreadsheet/Shared/OLE/PPS.php b/src/PhpSpreadsheet/Shared/OLE/PPS.php
index 2740a1b6da..6b487c36dd 100644
--- a/src/PhpSpreadsheet/Shared/OLE/PPS.php
+++ b/src/PhpSpreadsheet/Shared/OLE/PPS.php
@@ -203,7 +203,7 @@ public function getPpsWk()
      *
      * @return int The index for this PPS
      */
-    public static function savePpsSetPnt(&$raList, $to_save, $depth = 0)
+    public static function savePpsSetPnt(array &$raList, $to_save, $depth = 0)
     {
         if (!is_array($to_save) || (empty($to_save))) {
             return 0xFFFFFFFF;
diff --git a/src/PhpSpreadsheet/Shared/OLE/PPS/File.php b/src/PhpSpreadsheet/Shared/OLE/PPS/File.php
index dd1cda2de0..8a392817c5 100644
--- a/src/PhpSpreadsheet/Shared/OLE/PPS/File.php
+++ b/src/PhpSpreadsheet/Shared/OLE/PPS/File.php
@@ -44,10 +44,8 @@ public function __construct($name)
 
     /**
      * Initialization method. Has to be called right after OLE_PPS_File().
-     *
-     * @return mixed true on success
      */
-    public function init()
+    public function init(): bool
     {
         return true;
     }
@@ -57,7 +55,7 @@ public function init()
      *
      * @param string $data The data to append
      */
-    public function append($data): void
+    public function append(string $data): void
     {
         $this->_data .= $data;
     }
diff --git a/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php b/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
index e1cbf8c90d..5a1e5d4629 100644
--- a/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
+++ b/src/PhpSpreadsheet/Shared/OLE/PPS/Root.php
@@ -66,7 +66,7 @@ public function __construct($time_1st, $time_2nd, $raChild)
      *
      * @return bool true on success
      */
-    public function save($fileHandle)
+    public function save($fileHandle): bool
     {
         $this->fileHandle = $fileHandle;
 
@@ -106,7 +106,7 @@ public function save($fileHandle)
      *
      * @return float[] The array of numbers
      */
-    private function calcSize(&$raList)
+    private function calcSize(array &$raList): array
     {
         // Calculate Basic Setting
         [$iSBDcnt, $iBBcnt, $iPPScnt] = [0, 0, 0];
@@ -141,11 +141,9 @@ private function calcSize(&$raList)
      *
      * @param int $i2 The argument
      *
-     * @return float
-     *
      * @see save()
      */
-    private static function adjust2($i2)
+    private static function adjust2($i2): float
     {
         $iWk = log($i2) / log(2);
 
@@ -154,12 +152,8 @@ private static function adjust2($i2)
 
     /**
      * Save OLE header.
-     *
-     * @param int $iSBDcnt
-     * @param int $iBBcnt
-     * @param int $iPPScnt
      */
-    private function saveHeader($iSBDcnt, $iBBcnt, $iPPScnt): void
+    private function saveHeader(int $iSBDcnt, int $iBBcnt, int $iPPScnt): void
     {
         $FILE = $this->fileHandle;
 
@@ -235,10 +229,9 @@ private function saveHeader($iSBDcnt, $iBBcnt, $iPPScnt): void
     /**
      * Saving big data (PPS's with data bigger than \PhpOffice\PhpSpreadsheet\Shared\OLE::OLE_DATA_SIZE_SMALL).
      *
-     * @param int $iStBlk
      * @param array $raList Reference to array of PPS's
      */
-    private function saveBigData($iStBlk, &$raList): void
+    private function saveBigData(int $iStBlk, array &$raList): void
     {
         $FILE = $this->fileHandle;
 
@@ -267,10 +260,8 @@ private function saveBigData($iStBlk, &$raList): void
      * get small data (PPS's with data smaller than \PhpOffice\PhpSpreadsheet\Shared\OLE::OLE_DATA_SIZE_SMALL).
      *
      * @param array $raList Reference to array of PPS's
-     *
-     * @return string
      */
-    private function makeSmallData(&$raList)
+    private function makeSmallData(array &$raList): string
     {
         $sRes = '';
         $FILE = $this->fileHandle;
@@ -320,7 +311,7 @@ private function makeSmallData(&$raList)
      *
      * @param array $raList Reference to an array with all PPS's
      */
-    private function savePps(&$raList): void
+    private function savePps(array &$raList): void
     {
         // Save each PPS WK
         $iC = count($raList);
@@ -337,12 +328,8 @@ private function savePps(&$raList): void
 
     /**
      * Saving Big Block Depot.
-     *
-     * @param int $iSbdSize
-     * @param int $iBsize
-     * @param int $iPpsCnt
      */
-    private function saveBbd($iSbdSize, $iBsize, $iPpsCnt): void
+    private function saveBbd(int $iSbdSize, int $iBsize, int $iPpsCnt): void
     {
         $FILE = $this->fileHandle;
         // Calculate Basic Setting
diff --git a/src/PhpSpreadsheet/Shared/OLERead.php b/src/PhpSpreadsheet/Shared/OLERead.php
index fcc9639530..e15e9dac94 100644
--- a/src/PhpSpreadsheet/Shared/OLERead.php
+++ b/src/PhpSpreadsheet/Shared/OLERead.php
@@ -190,10 +190,8 @@ public function read(string $filename): void
      * Extract binary stream data.
      *
      * @param ?int $stream
-     *
-     * @return null|string
      */
-    public function getStream($stream)
+    public function getStream($stream): ?string
     {
         if ($stream === null) {
             return null;
@@ -242,7 +240,7 @@ public function getStream($stream)
      *
      * @return string Data for standard stream
      */
-    private function readData($block)
+    private function readData($block): string
     {
         $data = '';
 
@@ -317,12 +315,9 @@ private function readPropertySets(): void
     /**
      * Read 4 bytes of data at specified position.
      *
-     * @param string $data
      * @param int $pos
-     *
-     * @return int
      */
-    private static function getInt4d($data, $pos)
+    private static function getInt4d(string $data, $pos): int
     {
         if ($pos < 0) {
             // Invalid position
diff --git a/src/PhpSpreadsheet/Shared/StringHelper.php b/src/PhpSpreadsheet/Shared/StringHelper.php
index f30a9bd2d8..988f7a7d10 100644
--- a/src/PhpSpreadsheet/Shared/StringHelper.php
+++ b/src/PhpSpreadsheet/Shared/StringHelper.php
@@ -288,10 +288,8 @@ private static function buildCharacterSets(): void
      * element or in the shared string <t> element.
      *
      * @param string $textValue Value to unescape
-     *
-     * @return string
      */
-    public static function controlCharacterOOXML2PHP($textValue)
+    public static function controlCharacterOOXML2PHP($textValue): string
     {
         self::buildCharacterSets();
 
@@ -310,10 +308,8 @@ public static function controlCharacterOOXML2PHP($textValue)
      * element or in the shared string <t> element.
      *
      * @param string $textValue Value to escape
-     *
-     * @return string
      */
-    public static function controlCharacterPHP2OOXML($textValue)
+    public static function controlCharacterPHP2OOXML($textValue): string
     {
         self::buildCharacterSets();
 
diff --git a/src/PhpSpreadsheet/Shared/Trend/BestFit.php b/src/PhpSpreadsheet/Shared/Trend/BestFit.php
index a8d7c93b7d..29dbbed040 100644
--- a/src/PhpSpreadsheet/Shared/Trend/BestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/BestFit.php
@@ -20,10 +20,8 @@ abstract class BestFit
 
     /**
      * Number of entries in the sets of x- and y-value arrays.
-     *
-     * @var int
      */
-    protected $valueCount = 0;
+    protected int $valueCount;
 
     /**
      * X-value dataseries of values.
@@ -430,7 +428,7 @@ private function sumSquares(array $values)
     {
         return array_sum(
             array_map(
-                function ($value) {
+                function ($value): float|int {
                     return $value ** 2;
                 },
                 $values
diff --git a/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php b/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php
index eb8cd746d3..ebefd9c004 100644
--- a/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/ExponentialBestFit.php
@@ -19,7 +19,7 @@ class ExponentialBestFit extends BestFit
      *
      * @return float Y-Value
      */
-    public function getValueOfYForX($xValue)
+    public function getValueOfYForX($xValue): float
     {
         return $this->getIntersect() * $this->getSlope() ** ($xValue - $this->xOffset);
     }
@@ -31,7 +31,7 @@ public function getValueOfYForX($xValue)
      *
      * @return float X-Value
      */
-    public function getValueOfXForY($yValue)
+    public function getValueOfXForY($yValue): float
     {
         return log(($yValue + $this->yOffset) / $this->getIntersect()) / log($this->getSlope());
     }
@@ -40,10 +40,8 @@ public function getValueOfXForY($yValue)
      * Return the Equation of the best-fit line.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return string
      */
-    public function getEquation($dp = 0)
+    public function getEquation($dp = 0): string
     {
         $slope = $this->getSlope($dp);
         $intersect = $this->getIntersect($dp);
@@ -55,10 +53,8 @@ public function getEquation($dp = 0)
      * Return the Slope of the line.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return float
      */
-    public function getSlope($dp = 0)
+    public function getSlope($dp = 0): float
     {
         if ($dp != 0) {
             return round(exp($this->slope), $dp);
@@ -71,10 +67,8 @@ public function getSlope($dp = 0)
      * Return the Value of X where it intersects Y = 0.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return float
      */
-    public function getIntersect($dp = 0)
+    public function getIntersect($dp = 0): float
     {
         if ($dp != 0) {
             return round(exp($this->intersect), $dp);
@@ -92,7 +86,7 @@ public function getIntersect($dp = 0)
     private function exponentialRegression(array $yValues, array $xValues, bool $const): void
     {
         $adjustedYValues = array_map(
-            function ($value) {
+            function ($value): float {
                 return ($value < 0.0) ? 0 - log(abs($value)) : log($value);
             },
             $yValues
diff --git a/src/PhpSpreadsheet/Shared/Trend/LinearBestFit.php b/src/PhpSpreadsheet/Shared/Trend/LinearBestFit.php
index 65d6b4ff44..ef03b84050 100644
--- a/src/PhpSpreadsheet/Shared/Trend/LinearBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/LinearBestFit.php
@@ -19,7 +19,7 @@ class LinearBestFit extends BestFit
      *
      * @return float Y-Value
      */
-    public function getValueOfYForX($xValue)
+    public function getValueOfYForX($xValue): int|float
     {
         return $this->getIntersect() + $this->getSlope() * $xValue;
     }
@@ -31,7 +31,7 @@ public function getValueOfYForX($xValue)
      *
      * @return float X-Value
      */
-    public function getValueOfXForY($yValue)
+    public function getValueOfXForY($yValue): int|float
     {
         return ($yValue - $this->getIntersect()) / $this->getSlope();
     }
@@ -40,10 +40,8 @@ public function getValueOfXForY($yValue)
      * Return the Equation of the best-fit line.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return string
      */
-    public function getEquation($dp = 0)
+    public function getEquation($dp = 0): string
     {
         $slope = $this->getSlope($dp);
         $intersect = $this->getIntersect($dp);
diff --git a/src/PhpSpreadsheet/Shared/Trend/LogarithmicBestFit.php b/src/PhpSpreadsheet/Shared/Trend/LogarithmicBestFit.php
index 2366dc636a..1f91545fe6 100644
--- a/src/PhpSpreadsheet/Shared/Trend/LogarithmicBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/LogarithmicBestFit.php
@@ -19,7 +19,7 @@ class LogarithmicBestFit extends BestFit
      *
      * @return float Y-Value
      */
-    public function getValueOfYForX($xValue)
+    public function getValueOfYForX($xValue): float
     {
         return $this->getIntersect() + $this->getSlope() * log($xValue - $this->xOffset);
     }
@@ -31,7 +31,7 @@ public function getValueOfYForX($xValue)
      *
      * @return float X-Value
      */
-    public function getValueOfXForY($yValue)
+    public function getValueOfXForY($yValue): float
     {
         return exp(($yValue - $this->getIntersect()) / $this->getSlope());
     }
@@ -40,10 +40,8 @@ public function getValueOfXForY($yValue)
      * Return the Equation of the best-fit line.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return string
      */
-    public function getEquation($dp = 0)
+    public function getEquation($dp = 0): string
     {
         $slope = $this->getSlope($dp);
         $intersect = $this->getIntersect($dp);
@@ -60,7 +58,7 @@ public function getEquation($dp = 0)
     private function logarithmicRegression(array $yValues, array $xValues, bool $const): void
     {
         $adjustedYValues = array_map(
-            function ($value) {
+            function ($value): float {
                 return ($value < 0.0) ? 0 - log(abs($value)) : log($value);
             },
             $yValues
diff --git a/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php b/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
index 222a423004..86131f42a3 100644
--- a/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/PolynomialBestFit.php
@@ -64,7 +64,7 @@ public function getValueOfYForX($xValue)
      *
      * @return float X-Value
      */
-    public function getValueOfXForY($yValue)
+    public function getValueOfXForY($yValue): int|float
     {
         return ($yValue - $this->getIntersect()) / $this->getSlope();
     }
@@ -73,10 +73,8 @@ public function getValueOfXForY($yValue)
      * Return the Equation of the best-fit line.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return string
      */
-    public function getEquation($dp = 0)
+    public function getEquation($dp = 0): string
     {
         $slope = $this->getSlope($dp);
         $intersect = $this->getIntersect($dp);
@@ -122,10 +120,8 @@ public function getSlope($dp = 0)
 
     /**
      * @param int $dp
-     *
-     * @return array
      */
-    public function getCoefficients($dp = 0)
+    public function getCoefficients($dp = 0): array
     {
         // Phpstan and Scrutinizer are both correct - getSlope returns float, not array.
         // @phpstan-ignore-next-line
@@ -139,7 +135,7 @@ public function getCoefficients($dp = 0)
      * @param float[] $yValues The set of Y-values for this regression
      * @param float[] $xValues The set of X-values for this regression
      */
-    private function polynomialRegression($order, $yValues, $xValues): void
+    private function polynomialRegression($order, array $yValues, array $xValues): void
     {
         // calculate sums
         $x_sum = array_sum($xValues);
diff --git a/src/PhpSpreadsheet/Shared/Trend/PowerBestFit.php b/src/PhpSpreadsheet/Shared/Trend/PowerBestFit.php
index cafd01158e..e1955919a0 100644
--- a/src/PhpSpreadsheet/Shared/Trend/PowerBestFit.php
+++ b/src/PhpSpreadsheet/Shared/Trend/PowerBestFit.php
@@ -19,7 +19,7 @@ class PowerBestFit extends BestFit
      *
      * @return float Y-Value
      */
-    public function getValueOfYForX($xValue)
+    public function getValueOfYForX($xValue): float
     {
         return $this->getIntersect() * ($xValue - $this->xOffset) ** $this->getSlope();
     }
@@ -31,7 +31,7 @@ public function getValueOfYForX($xValue)
      *
      * @return float X-Value
      */
-    public function getValueOfXForY($yValue)
+    public function getValueOfXForY($yValue): float
     {
         return (($yValue + $this->yOffset) / $this->getIntersect()) ** (1 / $this->getSlope());
     }
@@ -40,10 +40,8 @@ public function getValueOfXForY($yValue)
      * Return the Equation of the best-fit line.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return string
      */
-    public function getEquation($dp = 0)
+    public function getEquation($dp = 0): string
     {
         $slope = $this->getSlope($dp);
         $intersect = $this->getIntersect($dp);
@@ -55,10 +53,8 @@ public function getEquation($dp = 0)
      * Return the Value of X where it intersects Y = 0.
      *
      * @param int $dp Number of places of decimal precision to display
-     *
-     * @return float
      */
-    public function getIntersect($dp = 0)
+    public function getIntersect($dp = 0): float
     {
         if ($dp != 0) {
             return round(exp($this->intersect), $dp);
@@ -76,13 +72,13 @@ public function getIntersect($dp = 0)
     private function powerRegression(array $yValues, array $xValues, bool $const): void
     {
         $adjustedYValues = array_map(
-            function ($value) {
+            function ($value): float {
                 return ($value < 0.0) ? 0 - log(abs($value)) : log($value);
             },
             $yValues
         );
         $adjustedXValues = array_map(
-            function ($value) {
+            function ($value): float {
                 return ($value < 0.0) ? 0 - log(abs($value)) : log($value);
             },
             $xValues
diff --git a/src/PhpSpreadsheet/Shared/Trend/Trend.php b/src/PhpSpreadsheet/Shared/Trend/Trend.php
index 117848c778..62399ca3ad 100644
--- a/src/PhpSpreadsheet/Shared/Trend/Trend.php
+++ b/src/PhpSpreadsheet/Shared/Trend/Trend.php
@@ -49,14 +49,13 @@ class Trend
     private static $trendCache = [];
 
     /**
-     * @param string $trendType
      * @param array $yValues
      * @param array $xValues
      * @param bool $const
      *
      * @return mixed
      */
-    public static function calculate($trendType = self::TREND_BEST_FIT, $yValues = [], $xValues = [], $const = true)
+    public static function calculate(string $trendType = self::TREND_BEST_FIT, $yValues = [], $xValues = [], $const = true)
     {
         //    Calculate number of points in each dataset
         $nY = count($yValues);
diff --git a/src/PhpSpreadsheet/Shared/XMLWriter.php b/src/PhpSpreadsheet/Shared/XMLWriter.php
index d9f403d7ad..c0d880e849 100644
--- a/src/PhpSpreadsheet/Shared/XMLWriter.php
+++ b/src/PhpSpreadsheet/Shared/XMLWriter.php
@@ -15,10 +15,8 @@ class XMLWriter extends \XMLWriter
 
     /**
      * Temporary filename.
-     *
-     * @var string
      */
-    private $tempFileName = '';
+    private string $tempFileName = '';
 
     /**
      * Create a new XMLWriter instance.
@@ -90,10 +88,8 @@ public function getData()
      * Wrapper method for writeRaw.
      *
      * @param null|string|string[] $rawTextData
-     *
-     * @return bool
      */
-    public function writeRawData($rawTextData)
+    public function writeRawData($rawTextData): bool
     {
         if (is_array($rawTextData)) {
             $rawTextData = implode("\n", $rawTextData);
diff --git a/src/PhpSpreadsheet/Shared/Xls.php b/src/PhpSpreadsheet/Shared/Xls.php
index a67583441c..8c16e3cd46 100644
--- a/src/PhpSpreadsheet/Shared/Xls.php
+++ b/src/PhpSpreadsheet/Shared/Xls.php
@@ -61,7 +61,7 @@ public static function sizeCol(Worksheet $worksheet, $col = 'A')
      *
      * @return int The width in pixels
      */
-    public static function sizeRow(Worksheet $worksheet, $row = 1)
+    public static function sizeRow(Worksheet $worksheet, $row = 1): int
     {
         // default font of the workbook
         $font = $worksheet->getParentOrThrow()->getDefaultStyle()->getFont();
@@ -105,7 +105,7 @@ public static function sizeRow(Worksheet $worksheet, $row = 1)
      *
      * @return int Horizontal measured in pixels
      */
-    public static function getDistanceX(Worksheet $worksheet, $startColumn = 'A', $startOffsetX = 0, $endColumn = 'A', $endOffsetX = 0)
+    public static function getDistanceX(Worksheet $worksheet, $startColumn = 'A', $startOffsetX = 0, $endColumn = 'A', $endOffsetX = 0): int
     {
         $distanceX = 0;
 
@@ -136,7 +136,7 @@ public static function getDistanceX(Worksheet $worksheet, $startColumn = 'A', $s
      *
      * @return int Vertical distance measured in pixels
      */
-    public static function getDistanceY(Worksheet $worksheet, $startRow = 1, $startOffsetY = 0, $endRow = 1, $endOffsetY = 0)
+    public static function getDistanceY(Worksheet $worksheet, $startRow = 1, $startOffsetY = 0, $endRow = 1, $endOffsetY = 0): int
     {
         $distanceY = 0;
 
@@ -203,10 +203,8 @@ public static function getDistanceY(Worksheet $worksheet, $startRow = 1, $startO
      * @param int $offsetY Vertical offset in pixels
      * @param int $width Width in pixels
      * @param int $height Height in pixels
-     *
-     * @return null|array
      */
-    public static function oneAnchor2twoAnchor(Worksheet $worksheet, $coordinates, $offsetX, $offsetY, $width, $height)
+    public static function oneAnchor2twoAnchor(Worksheet $worksheet, string $coordinates, $offsetX, $offsetY, $width, $height): ?array
     {
         [$col_start, $row] = Coordinate::indexesFromString($coordinates);
         $row_start = $row - 1;
diff --git a/src/PhpSpreadsheet/Spreadsheet.php b/src/PhpSpreadsheet/Spreadsheet.php
index 5c398ee6a6..389fe4070c 100644
--- a/src/PhpSpreadsheet/Spreadsheet.php
+++ b/src/PhpSpreadsheet/Spreadsheet.php
@@ -4,6 +4,8 @@
 
 use JsonSerializable;
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
+use PhpOffice\PhpSpreadsheet\Document\Properties;
+use PhpOffice\PhpSpreadsheet\Document\Security;
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
 use PhpOffice\PhpSpreadsheet\Shared\File;
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
@@ -31,24 +33,18 @@ class Spreadsheet implements JsonSerializable
 
     /**
      * Unique ID.
-     *
-     * @var string
      */
-    private $uniqueID;
+    private string $uniqueID;
 
     /**
      * Document properties.
-     *
-     * @var Document\Properties
      */
-    private $properties;
+    private Properties $properties;
 
     /**
      * Document security.
-     *
-     * @var Document\Security
      */
-    private $security;
+    private Security $security;
 
     /**
      * Collection of Worksheet objects.
@@ -66,10 +62,8 @@ class Spreadsheet implements JsonSerializable
 
     /**
      * Active sheet index.
-     *
-     * @var int
      */
-    private $activeSheetIndex = 0;
+    private int $activeSheetIndex;
 
     /**
      * Named ranges.
@@ -80,10 +74,8 @@ class Spreadsheet implements JsonSerializable
 
     /**
      * CellXf supervisor.
-     *
-     * @var Style
      */
-    private $cellXfSupervisor;
+    private Style $cellXfSupervisor;
 
     /**
      * CellXf collection.
@@ -204,8 +196,7 @@ class Spreadsheet implements JsonSerializable
      */
     private $tabRatio = 600;
 
-    /** @var Theme */
-    private $theme;
+    private Theme $theme;
 
     public function getTheme(): Theme
     {
@@ -268,7 +259,7 @@ public function setMacrosCertificate($certificate): void
      *
      * @return bool true|false
      */
-    public function hasMacrosCertificate()
+    public function hasMacrosCertificate(): bool
     {
         return $this->macrosCertificate !== null;
     }
@@ -379,10 +370,8 @@ public function setUnparsedLoadedData(array $unparsedLoadedData): void
      * return the extension of a filename. Internal use for a array_map callback (php<5.3 don't like lambda function).
      *
      * @param mixed $path
-     *
-     * @return string
      */
-    private function getExtensionOnly($path)
+    private function getExtensionOnly($path): string
     {
         $extension = pathinfo($path, PATHINFO_EXTENSION);
 
@@ -429,20 +418,16 @@ public function getRibbonBinObjects($what = 'all')
 
     /**
      * This workbook have a custom UI ?
-     *
-     * @return bool
      */
-    public function hasRibbon()
+    public function hasRibbon(): bool
     {
         return $this->ribbonXMLData !== null;
     }
 
     /**
      * This workbook have additionnal object for the ribbon ?
-     *
-     * @return bool
      */
-    public function hasRibbonBinObjects()
+    public function hasRibbonBinObjects(): bool
     {
         return $this->ribbonBinObjects !== null;
     }
@@ -451,10 +436,8 @@ public function hasRibbonBinObjects()
      * Check if a sheet with a specified code name already exists.
      *
      * @param string $codeName Name of the worksheet to check
-     *
-     * @return bool
      */
-    public function sheetCodeNameExists($codeName)
+    public function sheetCodeNameExists($codeName): bool
     {
         return $this->getSheetByCodeName($codeName) !== null;
     }
@@ -594,10 +577,8 @@ public function getActiveSheet()
      * Create sheet and add it to this workbook.
      *
      * @param null|int $sheetIndex Index where sheet should go (0,1,..., or null for last)
-     *
-     * @return Worksheet
      */
-    public function createSheet($sheetIndex = null)
+    public function createSheet($sheetIndex = null): Worksheet
     {
         $newSheet = new Worksheet($this);
         $this->addSheet($newSheet, $sheetIndex);
@@ -609,10 +590,8 @@ public function createSheet($sheetIndex = null)
      * Check if a sheet with a specified name already exists.
      *
      * @param string $worksheetName Name of the worksheet to check
-     *
-     * @return bool
      */
-    public function sheetNameExists($worksheetName)
+    public function sheetNameExists($worksheetName): bool
     {
         return $this->getSheetByName($worksheetName) !== null;
     }
@@ -622,10 +601,8 @@ public function sheetNameExists($worksheetName)
      *
      * @param Worksheet $worksheet The worksheet to add
      * @param null|int $sheetIndex Index where sheet should go (0,1,..., or null for last)
-     *
-     * @return Worksheet
      */
-    public function addSheet(Worksheet $worksheet, $sheetIndex = null)
+    public function addSheet(Worksheet $worksheet, $sheetIndex = null): Worksheet
     {
         if ($this->sheetNameExists($worksheet->getTitle())) {
             throw new Exception(
@@ -770,7 +747,7 @@ public function getIndex(Worksheet $worksheet)
      *
      * @return int New sheet index
      */
-    public function setIndexByName($worksheetName, $newIndexPosition)
+    public function setIndexByName(string $worksheetName, $newIndexPosition)
     {
         $oldIndex = $this->getIndex($this->getSheetByNameOrThrow($worksheetName));
         $worksheet = array_splice(
@@ -790,10 +767,8 @@ public function setIndexByName($worksheetName, $newIndexPosition)
 
     /**
      * Get sheet count.
-     *
-     * @return int
      */
-    public function getSheetCount()
+    public function getSheetCount(): int
     {
         return count($this->workSheetCollection);
     }
@@ -836,7 +811,7 @@ public function setActiveSheetIndex($worksheetIndex)
      *
      * @return Worksheet
      */
-    public function setActiveSheetIndexByName($worksheetName)
+    public function setActiveSheetIndexByName(string $worksheetName)
     {
         if (($worksheet = $this->getSheetByName($worksheetName)) instanceof Worksheet) {
             $this->setActiveSheetIndex($this->getIndex($worksheet));
@@ -852,7 +827,7 @@ public function setActiveSheetIndexByName($worksheetName)
      *
      * @return string[]
      */
-    public function getSheetNames()
+    public function getSheetNames(): array
     {
         $returnValue = [];
         $worksheetCount = $this->getSheetCount();
@@ -868,10 +843,8 @@ public function getSheetNames()
      *
      * @param Worksheet $worksheet External sheet to add
      * @param null|int $sheetIndex Index where sheet should go (0,1,..., or null for last)
-     *
-     * @return Worksheet
      */
-    public function addExternalSheet(Worksheet $worksheet, $sheetIndex = null)
+    public function addExternalSheet(Worksheet $worksheet, $sheetIndex = null): Worksheet
     {
         if ($this->sheetNameExists($worksheet->getTitle())) {
             throw new Exception("Workbook already contains a worksheet named '{$worksheet->getTitle()}'. Rename the external sheet first.");
@@ -919,7 +892,7 @@ public function getNamedRanges(): array
     {
         return array_filter(
             $this->definedNames,
-            function (DefinedName $definedName) {
+            function (DefinedName $definedName): bool {
                 return $definedName->isFormula() === self::DEFINED_NAME_IS_RANGE;
             }
         );
@@ -934,7 +907,7 @@ public function getNamedFormulae(): array
     {
         return array_filter(
             $this->definedNames,
-            function (DefinedName $definedName) {
+            function (DefinedName $definedName): bool {
                 return $definedName->isFormula() === self::DEFINED_NAME_IS_FORMULA;
             }
         );
@@ -1130,20 +1103,16 @@ public function removeDefinedName(string $definedName, ?Worksheet $worksheet = n
 
     /**
      * Get worksheet iterator.
-     *
-     * @return Iterator
      */
-    public function getWorksheetIterator()
+    public function getWorksheetIterator(): Iterator
     {
         return new Iterator($this);
     }
 
     /**
      * Copy workbook (!= clone!).
-     *
-     * @return Spreadsheet
      */
-    public function copy()
+    public function copy(): self
     {
         $filename = File::temporaryFilename();
         $writer = new XlsxWriter($this);
@@ -1207,10 +1176,8 @@ public function getCellXfByHashCode($hashcode)
 
     /**
      * Check if style exists in style collection.
-     *
-     * @return bool
      */
-    public function cellXfExists(Style $cellStyleIndex)
+    public function cellXfExists(Style $cellStyleIndex): bool
     {
         return in_array($cellStyleIndex, $this->cellXfCollection, true);
     }
diff --git a/src/PhpSpreadsheet/Style/Alignment.php b/src/PhpSpreadsheet/Style/Alignment.php
index 68edfaca40..07fd71ebdd 100644
--- a/src/PhpSpreadsheet/Style/Alignment.php
+++ b/src/PhpSpreadsheet/Style/Alignment.php
@@ -181,10 +181,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['alignment' => $array];
     }
@@ -207,7 +205,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())
@@ -260,7 +258,7 @@ public function getHorizontal()
      *
      * @return $this
      */
-    public function setHorizontal(string $horizontalAlignment)
+    public function setHorizontal(string $horizontalAlignment): static
     {
         $horizontalAlignment = strtolower($horizontalAlignment);
         if ($horizontalAlignment === self::HORIZONTAL_CENTER_CONTINUOUS_LC) {
@@ -298,7 +296,7 @@ public function getVertical()
      *
      * @return $this
      */
-    public function setVertical($verticalAlignment)
+    public function setVertical($verticalAlignment): static
     {
         $verticalAlignment = strtolower($verticalAlignment);
 
@@ -333,7 +331,7 @@ public function getTextRotation()
      *
      * @return $this
      */
-    public function setTextRotation($angleInDegrees)
+    public function setTextRotation($angleInDegrees): static
     {
         // Excel2007 value 255 => PhpSpreadsheet value -165
         if ($angleInDegrees == self::TEXTROTATION_STACK_EXCEL) {
@@ -376,7 +374,7 @@ public function getWrapText()
      *
      * @return $this
      */
-    public function setWrapText($wrapped)
+    public function setWrapText($wrapped): static
     {
         if ($wrapped == '') {
             $wrapped = false;
@@ -412,7 +410,7 @@ public function getShrinkToFit()
      *
      * @return $this
      */
-    public function setShrinkToFit($shrink)
+    public function setShrinkToFit($shrink): static
     {
         if ($shrink == '') {
             $shrink = false;
@@ -448,7 +446,7 @@ public function getIndent()
      *
      * @return $this
      */
-    public function setIndent($indent)
+    public function setIndent($indent): static
     {
         if ($indent > 0) {
             if (
@@ -491,7 +489,7 @@ public function getReadOrder()
      *
      * @return $this
      */
-    public function setReadOrder($readOrder)
+    public function setReadOrder($readOrder): static
     {
         if ($readOrder < 0 || $readOrder > 2) {
             $readOrder = 0;
diff --git a/src/PhpSpreadsheet/Style/Border.php b/src/PhpSpreadsheet/Style/Border.php
index 568e1e006a..ae34e04447 100644
--- a/src/PhpSpreadsheet/Style/Border.php
+++ b/src/PhpSpreadsheet/Style/Border.php
@@ -32,10 +32,8 @@ class Border extends Supervisor
 
     /**
      * Border color.
-     *
-     * @var Color
      */
-    protected $color;
+    protected Color $color;
 
     /**
      * @var null|int
@@ -99,10 +97,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         /** @var Style */
         $parent = $this->parent;
@@ -128,7 +124,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -167,7 +163,7 @@ public function getBorderStyle()
      *
      * @return $this
      */
-    public function setBorderStyle($style)
+    public function setBorderStyle($style): static
     {
         if (empty($style)) {
             $style = self::BORDER_NONE;
@@ -200,7 +196,7 @@ public function getColor()
      *
      * @return $this
      */
-    public function setColor(Color $color)
+    public function setColor(Color $color): static
     {
         // make sure parameter is a real color and not a supervisor
         $color = $color->getIsSupervisor() ? $color->getSharedComponent() : $color;
diff --git a/src/PhpSpreadsheet/Style/Borders.php b/src/PhpSpreadsheet/Style/Borders.php
index a1247e859d..814511faf4 100644
--- a/src/PhpSpreadsheet/Style/Borders.php
+++ b/src/PhpSpreadsheet/Style/Borders.php
@@ -14,45 +14,33 @@ class Borders extends Supervisor
 
     /**
      * Left.
-     *
-     * @var Border
      */
-    protected $left;
+    protected Border $left;
 
     /**
      * Right.
-     *
-     * @var Border
      */
-    protected $right;
+    protected Border $right;
 
     /**
      * Top.
-     *
-     * @var Border
      */
-    protected $top;
+    protected Border $top;
 
     /**
      * Bottom.
-     *
-     * @var Border
      */
-    protected $bottom;
+    protected Border $bottom;
 
     /**
      * Diagonal.
-     *
-     * @var Border
      */
-    protected $diagonal;
+    protected Border $diagonal;
 
     /**
      * DiagonalDirection.
-     *
-     * @var int
      */
-    protected $diagonalDirection;
+    protected int $diagonalDirection;
 
     /**
      * All borders pseudo-border. Only applies to supervisor.
@@ -150,10 +138,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['borders' => $array];
     }
@@ -197,7 +183,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -372,7 +358,7 @@ public function getDiagonalDirection()
      *
      * @return $this
      */
-    public function setDiagonalDirection($direction)
+    public function setDiagonalDirection($direction): static
     {
         if ($direction == '') {
             $direction = self::DIAGONAL_NONE;
diff --git a/src/PhpSpreadsheet/Style/Color.php b/src/PhpSpreadsheet/Style/Color.php
index 282defc0ce..16dc238c9f 100644
--- a/src/PhpSpreadsheet/Style/Color.php
+++ b/src/PhpSpreadsheet/Style/Color.php
@@ -163,10 +163,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         /** @var Style */
         $parent = $this->parent;
@@ -185,7 +183,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -239,7 +237,7 @@ public function getARGB(): ?string
      *
      * @return $this
      */
-    public function setARGB(?string $colorValue = self::COLOR_BLACK)
+    public function setARGB(?string $colorValue = self::COLOR_BLACK): static
     {
         $this->hasChanged = true;
         $colorValue = $this->validateColor($colorValue);
@@ -276,7 +274,7 @@ public function getRGB(): string
      *
      * @return $this
      */
-    public function setRGB(?string $colorValue = self::COLOR_BLACK)
+    public function setRGB(?string $colorValue = self::COLOR_BLACK): static
     {
         return $this->setARGB($colorValue);
     }
@@ -291,7 +289,7 @@ public function setRGB(?string $colorValue = self::COLOR_BLACK)
      *
      * @return int|string The extracted colour component
      */
-    private static function getColourComponent($rgbValue, $offset, $hex = true)
+    private static function getColourComponent($rgbValue, $offset, $hex = true): string|int
     {
         $colour = substr($rgbValue, $offset, 2) ?: '';
         if (preg_match('/^[0-9a-f]{2}$/i', $colour) !== 1) {
@@ -351,7 +349,7 @@ public static function getBlue($rgbValue, $hex = true)
      *
      * @return string The adjusted colour as an RGBA or RGB value (e.g. FF00CCCC or CCDDEE)
      */
-    public static function changeBrightness($hexColourValue, $adjustPercentage)
+    public static function changeBrightness($hexColourValue, $adjustPercentage): string
     {
         $rgba = (strlen($hexColourValue) === 8);
         $adjustPercentage = max(-1.0, min(1.0, $adjustPercentage));
diff --git a/src/PhpSpreadsheet/Style/Conditional.php b/src/PhpSpreadsheet/Style/Conditional.php
index 36069b00c8..7785f5cae9 100644
--- a/src/PhpSpreadsheet/Style/Conditional.php
+++ b/src/PhpSpreadsheet/Style/Conditional.php
@@ -110,10 +110,8 @@ class Conditional implements IComparable
 
     /**
      * Style.
-     *
-     * @var Style
      */
-    private $style;
+    private Style $style;
 
     /** @var bool */
     private $noFormatSet = false;
@@ -156,7 +154,7 @@ public function getConditionType()
      *
      * @return $this
      */
-    public function setConditionType($type)
+    public function setConditionType($type): static
     {
         $this->conditionType = $type;
 
@@ -180,7 +178,7 @@ public function getOperatorType()
      *
      * @return $this
      */
-    public function setOperatorType($type)
+    public function setOperatorType($type): static
     {
         $this->operatorType = $type;
 
@@ -204,7 +202,7 @@ public function getText()
      *
      * @return $this
      */
-    public function setText($text)
+    public function setText($text): static
     {
         $this->text = $text;
 
@@ -228,7 +226,7 @@ public function getStopIfTrue()
      *
      * @return $this
      */
-    public function setStopIfTrue($stopIfTrue)
+    public function setStopIfTrue($stopIfTrue): static
     {
         $this->stopIfTrue = $stopIfTrue;
 
@@ -252,7 +250,7 @@ public function getConditions()
      *
      * @return $this
      */
-    public function setConditions($conditions)
+    public function setConditions($conditions): static
     {
         if (!is_array($conditions)) {
             $conditions = [$conditions];
@@ -269,7 +267,7 @@ public function setConditions($conditions)
      *
      * @return $this
      */
-    public function addCondition($condition)
+    public function addCondition($condition): static
     {
         $this->condition[] = $condition;
 
@@ -291,7 +289,7 @@ public function getStyle()
      *
      * @return $this
      */
-    public function setStyle(Style $style)
+    public function setStyle(Style $style): static
     {
         $this->style = $style;
 
@@ -313,7 +311,7 @@ public function getDataBar()
      *
      * @return $this
      */
-    public function setDataBar(ConditionalDataBar $dataBar)
+    public function setDataBar(ConditionalDataBar $dataBar): static
     {
         $this->dataBar = $dataBar;
 
@@ -325,7 +323,7 @@ public function setDataBar(ConditionalDataBar $dataBar)
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->conditionType .
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/CellMatcher.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/CellMatcher.php
index 7ead9a5ccb..06c19e0123 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/CellMatcher.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/CellMatcher.php
@@ -30,20 +30,14 @@ class CellMatcher
         Conditional::CONDITION_UNIQUE => "COUNTIF('%s'!%s,%s)=1",
     ];
 
-    /**
-     * @var Cell
-     */
-    protected $cell;
+    protected Cell $cell;
 
     /**
      * @var int
      */
     protected $cellRow;
 
-    /**
-     * @var Worksheet
-     */
-    protected $worksheet;
+    protected Worksheet $worksheet;
 
     /**
      * @var int
@@ -70,10 +64,7 @@ class CellMatcher
      */
     protected $referenceColumn;
 
-    /**
-     * @var Calculation
-     */
-    protected $engine;
+    protected Calculation $engine;
 
     public function __construct(Cell $cell, string $conditionalRange)
     {
@@ -147,11 +138,9 @@ public function evaluateConditional(Conditional $conditional): bool
     }
 
     /**
-     * @param mixed $value
-     *
      * @return float|int|string
      */
-    protected function wrapValue($value)
+    protected function wrapValue(mixed $value)
     {
         if (!is_numeric($value)) {
             if (is_bool($value)) {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/CellStyleAssessor.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/CellStyleAssessor.php
index 4c000db32a..30f5c97296 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/CellStyleAssessor.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/CellStyleAssessor.php
@@ -8,15 +8,9 @@
 
 class CellStyleAssessor
 {
-    /**
-     * @var CellMatcher
-     */
-    protected $cellMatcher;
+    protected CellMatcher $cellMatcher;
 
-    /**
-     * @var StyleMerger
-     */
-    protected $styleMerger;
+    protected StyleMerger $styleMerger;
 
     public function __construct(Cell $cell, string $conditionalRange)
     {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalDataBar.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalDataBar.php
index c5c36aeb32..c07c753b8b 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalDataBar.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalDataBar.php
@@ -9,21 +9,13 @@ class ConditionalDataBar
     /** @var null|bool */
     private $showValue;
 
-    /** <dataBar> children */
+    private ?ConditionalFormatValueObject $minimumConditionalFormatValueObject = null;
 
-    /** @var ?ConditionalFormatValueObject */
-    private $minimumConditionalFormatValueObject;
+    private ?ConditionalFormatValueObject $maximumConditionalFormatValueObject = null;
 
-    /** @var ?ConditionalFormatValueObject */
-    private $maximumConditionalFormatValueObject;
+    private string $color = '';
 
-    /** @var string */
-    private $color;
-
-    /** <extLst> */
-
-    /** @var ?ConditionalFormattingRuleExtension */
-    private $conditionalFormattingRuleExt;
+    private ?ConditionalFormattingRuleExtension $conditionalFormattingRuleExt = null;
 
     /**
      * @return null|bool
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php
index 0cdbc36851..e19e6d5555 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/ConditionalFormattingRuleExtension.php
@@ -9,21 +9,15 @@ class ConditionalFormattingRuleExtension
 {
     const CONDITION_EXTENSION_DATABAR = 'dataBar';
 
-    /** <conditionalFormatting> attributes */
-
-    /** @var string */
-    private $id;
+    private string $id;
 
     /** @var string Conditional Formatting Rule */
-    private $cfRule;
-
-    /** <conditionalFormatting> children */
+    private string $cfRule;
 
-    /** @var ConditionalDataBarExtension */
-    private $dataBar;
+    private ConditionalDataBarExtension $dataBar;
 
     /** @var string Sequence of References */
-    private $sqref;
+    private string $sqref = '';
 
     /**
      * ConditionalFormattingRuleExtension constructor.
@@ -124,8 +118,7 @@ private static function parseExtDataBarAttributesFromXml(
         }
     }
 
-    /** @param array|SimpleXMLElement $ns */
-    private static function parseExtDataBarElementChildrenFromXml(ConditionalDataBarExtension $extDataBarObj, SimpleXMLElement $dataBarXml, $ns): void
+    private static function parseExtDataBarElementChildrenFromXml(ConditionalDataBarExtension $extDataBarObj, SimpleXMLElement $dataBarXml, array $ns): void
     {
         if ($dataBarXml->borderColor) {
             $attributes = $dataBarXml->borderColor->attributes();
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/StyleMerger.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/StyleMerger.php
index 0ddc07f2a7..9388848e74 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/StyleMerger.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/StyleMerger.php
@@ -10,10 +10,7 @@
 
 class StyleMerger
 {
-    /**
-     * @var Style
-     */
-    protected $baseStyle;
+    protected Style $baseStyle;
 
     public function __construct(Style $baseStyle)
     {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard.php
index d5d56a9a3d..69b524a636 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard.php
@@ -24,10 +24,7 @@ class Wizard
     public const VALUE_TYPE_CELL = 'cell';
     public const VALUE_TYPE_FORMULA = 'formula';
 
-    /**
-     * @var string
-     */
-    protected $cellRange;
+    protected string $cellRange;
 
     public function __construct(string $cellRange)
     {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Blanks.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Blanks.php
index 14f30d39e1..aa2da2f1e2 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Blanks.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Blanks.php
@@ -26,10 +26,7 @@ class Blanks extends WizardAbstract implements WizardInterface
         Wizard::BLANKS => 'LEN(TRIM(%s))=0',
     ];
 
-    /**
-     * @var bool
-     */
-    protected $inverse;
+    protected bool $inverse;
 
     public function __construct(string $cellRange, bool $inverse = false)
     {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/CellValue.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/CellValue.php
index 265b2419b9..d99e83551e 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/CellValue.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/CellValue.php
@@ -165,7 +165,7 @@ public static function fromConditional(Conditional $conditional, string $cellRan
      * @param string $methodName
      * @param mixed[] $arguments
      */
-    public function __call($methodName, $arguments): self
+    public function __call($methodName, array $arguments): self
     {
         if (!isset(self::MAGIC_OPERATIONS[$methodName]) && $methodName !== 'and') {
             throw new Exception('Invalid Operator for Cell Value CF Rule Wizard');
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Duplicates.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Duplicates.php
index 3f063fefd5..56ddd1eeb4 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Duplicates.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Duplicates.php
@@ -16,10 +16,7 @@ class Duplicates extends WizardAbstract implements WizardInterface
         'unique' => true,
     ];
 
-    /**
-     * @var bool
-     */
-    protected $inverse;
+    protected bool $inverse;
 
     public function __construct(string $cellRange, bool $inverse = false)
     {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Errors.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Errors.php
index 56b9086c8d..e5fb329d67 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Errors.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Errors.php
@@ -22,10 +22,7 @@ class Errors extends WizardAbstract implements WizardInterface
         Wizard::ERRORS => 'ISERROR(%s)',
     ];
 
-    /**
-     * @var bool
-     */
-    protected $inverse;
+    protected bool $inverse;
 
     public function __construct(string $cellRange, bool $inverse = false)
     {
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Expression.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Expression.php
index e6d29f7be9..5064df6a26 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Expression.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/Expression.php
@@ -60,7 +60,7 @@ public static function fromConditional(Conditional $conditional, string $cellRan
      * @param string $methodName
      * @param mixed[] $arguments
      */
-    public function __call($methodName, $arguments): self
+    public function __call($methodName, array $arguments): self
     {
         if ($methodName !== 'formula') {
             throw new Exception('Invalid Operation for Expression CF Rule Wizard');
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/TextValue.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/TextValue.php
index 987cfbf8b9..91b8a0d1eb 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/TextValue.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/TextValue.php
@@ -145,7 +145,7 @@ public static function fromConditional(Conditional $conditional, string $cellRan
      * @param string $methodName
      * @param mixed[] $arguments
      */
-    public function __call($methodName, $arguments): self
+    public function __call($methodName, array $arguments): self
     {
         if (!isset(self::MAGIC_OPERATIONS[$methodName])) {
             throw new Exception('Invalid Operation for Text Value CF Rule Wizard');
diff --git a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/WizardAbstract.php b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/WizardAbstract.php
index 5644aab456..e747cef4c9 100644
--- a/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/WizardAbstract.php
+++ b/src/PhpSpreadsheet/Style/ConditionalFormatting/Wizard/WizardAbstract.php
@@ -19,10 +19,7 @@ abstract class WizardAbstract
      */
     protected $expression;
 
-    /**
-     * @var string
-     */
-    protected $cellRange;
+    protected string $cellRange;
 
     /**
      * @var string
@@ -136,7 +133,7 @@ public static function reverseAdjustCellRef(string $condition, string $cellRange
             if ($i) {
                 $value = (string) preg_replace_callback(
                     '/' . Calculation::CALCULATION_REGEXP_CELLREF_RELATIVE . '/i',
-                    function ($matches) use ($referenceColumnIndex, $referenceRow) {
+                    function ($matches) use ($referenceColumnIndex, $referenceRow): string {
                         return self::reverseCellAdjustment($matches, $referenceColumnIndex, $referenceRow);
                     },
                     $value
diff --git a/src/PhpSpreadsheet/Style/Fill.php b/src/PhpSpreadsheet/Style/Fill.php
index 28af444a48..1d1c3df470 100644
--- a/src/PhpSpreadsheet/Style/Fill.php
+++ b/src/PhpSpreadsheet/Style/Fill.php
@@ -53,17 +53,13 @@ class Fill extends Supervisor
 
     /**
      * Start color.
-     *
-     * @var Color
      */
-    protected $startColor;
+    protected Color $startColor;
 
     /**
      * End color.
-     *
-     * @var Color
      */
-    protected $endColor;
+    protected Color $endColor;
 
     /** @var bool */
     private $colorChanged = false;
@@ -115,10 +111,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['fill' => $array];
     }
@@ -145,7 +139,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -192,7 +186,7 @@ public function getFillType()
      *
      * @return $this
      */
-    public function setFillType($fillType)
+    public function setFillType($fillType): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['fillType' => $fillType]);
@@ -225,7 +219,7 @@ public function getRotation()
      *
      * @return $this
      */
-    public function setRotation($angleInDegrees)
+    public function setRotation($angleInDegrees): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['rotation' => $angleInDegrees]);
@@ -252,7 +246,7 @@ public function getStartColor()
      *
      * @return $this
      */
-    public function setStartColor(Color $color)
+    public function setStartColor(Color $color): static
     {
         $this->colorChanged = true;
         // make sure parameter is a real color and not a supervisor
@@ -283,7 +277,7 @@ public function getEndColor()
      *
      * @return $this
      */
-    public function setEndColor(Color $color)
+    public function setEndColor(Color $color): static
     {
         $this->colorChanged = true;
         // make sure parameter is a real color and not a supervisor
diff --git a/src/PhpSpreadsheet/Style/Font.php b/src/PhpSpreadsheet/Style/Font.php
index a8eeaa9861..45de032b27 100644
--- a/src/PhpSpreadsheet/Style/Font.php
+++ b/src/PhpSpreadsheet/Style/Font.php
@@ -97,10 +97,8 @@ class Font extends Supervisor
 
     /**
      * Foreground color.
-     *
-     * @var Color
      */
-    protected $color;
+    protected Color $color;
 
     /**
      * @var null|int
@@ -163,10 +161,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['font' => $array];
     }
@@ -193,7 +189,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -381,7 +377,7 @@ public function getSize()
      *
      * @return $this
      */
-    public function setSize($sizeInPoints, bool $nullOk = false)
+    public function setSize($sizeInPoints, bool $nullOk = false): static
     {
         if (is_string($sizeInPoints) || is_int($sizeInPoints)) {
             $sizeInPoints = (float) $sizeInPoints; // $pValue = 0 if given string is not numeric
@@ -426,7 +422,7 @@ public function getBold()
      *
      * @return $this
      */
-    public function setBold($bold)
+    public function setBold($bold): static
     {
         if ($bold == '') {
             $bold = false;
@@ -462,7 +458,7 @@ public function getItalic()
      *
      * @return $this
      */
-    public function setItalic($italic)
+    public function setItalic($italic): static
     {
         if ($italic == '') {
             $italic = false;
@@ -496,7 +492,7 @@ public function getSuperscript()
      *
      * @return $this
      */
-    public function setSuperscript(bool $superscript)
+    public function setSuperscript(bool $superscript): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['superscript' => $superscript]);
@@ -530,7 +526,7 @@ public function getSubscript()
      *
      * @return $this
      */
-    public function setSubscript(bool $subscript)
+    public function setSubscript(bool $subscript): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['subscript' => $subscript]);
@@ -671,7 +667,7 @@ public function getUnderline()
      *
      * @return $this
      */
-    public function setUnderline($underlineStyle)
+    public function setUnderline($underlineStyle): static
     {
         if (is_bool($underlineStyle)) {
             $underlineStyle = ($underlineStyle) ? self::UNDERLINE_SINGLE : self::UNDERLINE_NONE;
@@ -709,7 +705,7 @@ public function getStrikethrough()
      *
      * @return $this
      */
-    public function setStrikethrough($strikethru)
+    public function setStrikethrough($strikethru): static
     {
         if ($strikethru == '') {
             $strikethru = false;
@@ -740,7 +736,7 @@ public function getColor()
      *
      * @return $this
      */
-    public function setColor(Color $color)
+    public function setColor(Color $color): static
     {
         // make sure parameter is a real color and not a supervisor
         $color = $color->getIsSupervisor() ? $color->getSharedComponent() : $color;
diff --git a/src/PhpSpreadsheet/Style/NumberFormat.php b/src/PhpSpreadsheet/Style/NumberFormat.php
index b605cff6e9..84634fbe62 100644
--- a/src/PhpSpreadsheet/Style/NumberFormat.php
+++ b/src/PhpSpreadsheet/Style/NumberFormat.php
@@ -157,10 +157,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['numberFormat' => $array];
     }
@@ -180,7 +178,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -217,7 +215,7 @@ public function getFormatCode()
      *
      * @return $this
      */
-    public function setFormatCode(string $formatCode)
+    public function setFormatCode(string $formatCode): static
     {
         if ($formatCode == '') {
             $formatCode = self::FORMAT_GENERAL;
@@ -255,7 +253,7 @@ public function getBuiltInFormatCode()
      *
      * @return $this
      */
-    public function setBuiltInFormatCode(int $formatCodeIndex)
+    public function setBuiltInFormatCode(int $formatCodeIndex): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['formatCode' => self::builtInFormatCode($formatCodeIndex)]);
diff --git a/src/PhpSpreadsheet/Style/NumberFormat/Formatter.php b/src/PhpSpreadsheet/Style/NumberFormat/Formatter.php
index 41a17151d3..06c131e68e 100644
--- a/src/PhpSpreadsheet/Style/NumberFormat/Formatter.php
+++ b/src/PhpSpreadsheet/Style/NumberFormat/Formatter.php
@@ -157,7 +157,7 @@ public static function toFormattedString($value, $format, $callBack = null)
 
         $format = (string) preg_replace_callback(
             '/(["])(?:(?=(\\\\?))\\2.)*?\\1/u',
-            function ($matches) {
+            function (array $matches): string {
                 return str_replace('.', chr(0x00), $matches[0]);
             },
             $format
diff --git a/src/PhpSpreadsheet/Style/Protection.php b/src/PhpSpreadsheet/Style/Protection.php
index 1c174e7266..dff5f359c3 100644
--- a/src/PhpSpreadsheet/Style/Protection.php
+++ b/src/PhpSpreadsheet/Style/Protection.php
@@ -11,17 +11,13 @@ class Protection extends Supervisor
 
     /**
      * Locked.
-     *
-     * @var string
      */
-    protected $locked;
+    protected ?string $locked = null;
 
     /**
      * Hidden.
-     *
-     * @var string
      */
-    protected $hidden;
+    protected ?string $hidden = null;
 
     /**
      * Create a new Protection.
@@ -63,10 +59,8 @@ public function getSharedComponent()
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['protection' => $array];
     }
@@ -87,7 +81,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray)
+    public function applyFromArray(array $styleArray): static
     {
         if ($this->isSupervisor) {
             $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($this->getStyleArray($styleArray));
@@ -105,10 +99,8 @@ public function applyFromArray(array $styleArray)
 
     /**
      * Get locked.
-     *
-     * @return string
      */
-    public function getLocked()
+    public function getLocked(): ?string
     {
         if ($this->isSupervisor) {
             return $this->getSharedComponent()->getLocked();
@@ -124,7 +116,7 @@ public function getLocked()
      *
      * @return $this
      */
-    public function setLocked($lockType)
+    public function setLocked($lockType): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['locked' => $lockType]);
@@ -138,10 +130,8 @@ public function setLocked($lockType)
 
     /**
      * Get hidden.
-     *
-     * @return string
      */
-    public function getHidden()
+    public function getHidden(): ?string
     {
         if ($this->isSupervisor) {
             return $this->getSharedComponent()->getHidden();
@@ -157,7 +147,7 @@ public function getHidden()
      *
      * @return $this
      */
-    public function setHidden($hiddenType)
+    public function setHidden($hiddenType): static
     {
         if ($this->isSupervisor) {
             $styleArray = $this->getStyleArray(['hidden' => $hiddenType]);
diff --git a/src/PhpSpreadsheet/Style/RgbTint.php b/src/PhpSpreadsheet/Style/RgbTint.php
index 582ae48397..9c0ce7f129 100644
--- a/src/PhpSpreadsheet/Style/RgbTint.php
+++ b/src/PhpSpreadsheet/Style/RgbTint.php
@@ -72,7 +72,7 @@ private static function rgbToHls(float $red, float $green, float $blue): array
      *
      * @return float[]
      */
-    private static function hlsToRgb($hue, $luminance, $saturation): array
+    private static function hlsToRgb(float $hue, $luminance, $saturation): array
     {
         if ($saturation === self::$scrutinizerZeroPointZero) {
             return [$luminance, $luminance, $luminance];
diff --git a/src/PhpSpreadsheet/Style/Style.php b/src/PhpSpreadsheet/Style/Style.php
index 9309830bfa..6a288b4e60 100644
--- a/src/PhpSpreadsheet/Style/Style.php
+++ b/src/PhpSpreadsheet/Style/Style.php
@@ -12,45 +12,33 @@ class Style extends Supervisor
 {
     /**
      * Font.
-     *
-     * @var Font
      */
-    protected $font;
+    protected Font $font;
 
     /**
      * Fill.
-     *
-     * @var Fill
      */
-    protected $fill;
+    protected Fill $fill;
 
     /**
      * Borders.
-     *
-     * @var Borders
      */
-    protected $borders;
+    protected Borders $borders;
 
     /**
      * Alignment.
-     *
-     * @var Alignment
      */
-    protected $alignment;
+    protected Alignment $alignment;
 
     /**
      * Number Format.
-     *
-     * @var NumberFormat
      */
-    protected $numberFormat;
+    protected NumberFormat $numberFormat;
 
     /**
      * Protection.
-     *
-     * @var Protection
      */
-    protected $protection;
+    protected Protection $protection;
 
     /**
      * Index of style in collection. Only used for real style.
@@ -148,10 +136,8 @@ public function getParent(): Spreadsheet
      * Build style array from subcomponents.
      *
      * @param array $array
-     *
-     * @return array
      */
-    public function getStyleArray($array)
+    public function getStyleArray($array): array
     {
         return ['quotePrefix' => $array];
     }
@@ -201,7 +187,7 @@ public function getStyleArray($array)
      *
      * @return $this
      */
-    public function applyFromArray(array $styleArray, $advancedBorders = true)
+    public function applyFromArray(array $styleArray, $advancedBorders = true): static
     {
         if ($this->isSupervisor) {
             $pRange = $this->getSelectedCells();
@@ -583,7 +569,7 @@ public function getFont()
      *
      * @return $this
      */
-    public function setFont(Font $font)
+    public function setFont(Font $font): static
     {
         $this->font = $font;
 
@@ -625,7 +611,7 @@ public function getNumberFormat()
      *
      * @return Conditional[]
      */
-    public function getConditionalStyles()
+    public function getConditionalStyles(): array
     {
         return $this->getActiveSheet()->getConditionalStyles($this->getActiveCell());
     }
@@ -637,7 +623,7 @@ public function getConditionalStyles()
      *
      * @return $this
      */
-    public function setConditionalStyles(array $conditionalStyleArray)
+    public function setConditionalStyles(array $conditionalStyleArray): static
     {
         $this->getActiveSheet()->setConditionalStyles($this->getSelectedCells(), $conditionalStyleArray);
 
@@ -675,7 +661,7 @@ public function getQuotePrefix()
      *
      * @return $this
      */
-    public function setQuotePrefix($quotePrefix)
+    public function setQuotePrefix($quotePrefix): static
     {
         if ($quotePrefix == '') {
             $quotePrefix = false;
@@ -695,7 +681,7 @@ public function setQuotePrefix($quotePrefix)
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->fill->getHashCode() .
diff --git a/src/PhpSpreadsheet/Theme.php b/src/PhpSpreadsheet/Theme.php
index ab101f01ee..ac4dbe560c 100644
--- a/src/PhpSpreadsheet/Theme.php
+++ b/src/PhpSpreadsheet/Theme.php
@@ -4,11 +4,9 @@
 
 class Theme
 {
-    /** @var string */
-    private $themeColorName = 'Office';
+    private string $themeColorName = 'Office';
 
-    /** @var string */
-    private $themeFontName = 'Office';
+    private string $themeFontName = 'Office';
 
     public const COLOR_SCHEME_2013_PLUS_NAME = 'Office 2013+';
     public const COLOR_SCHEME_2013_PLUS = [
@@ -45,23 +43,17 @@ class Theme
     /** @var string[] */
     private $themeColors = self::COLOR_SCHEME_2007_2010;
 
-    /** @var string */
-    private $majorFontLatin = 'Cambria';
+    private string $majorFontLatin = 'Cambria';
 
-    /** @var string */
-    private $majorFontEastAsian = '';
+    private string $majorFontEastAsian = '';
 
-    /** @var string */
-    private $majorFontComplexScript = '';
+    private string $majorFontComplexScript = '';
 
-    /** @var string */
-    private $minorFontLatin = 'Calibri';
+    private string $minorFontLatin = 'Calibri';
 
-    /** @var string */
-    private $minorFontEastAsian = '';
+    private string $minorFontEastAsian = '';
 
-    /** @var string */
-    private $minorFontComplexScript = '';
+    private string $minorFontComplexScript = '';
 
     /**
      * Map of Major (header) fonts to write.
diff --git a/src/PhpSpreadsheet/Worksheet/AutoFilter.php b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
index 62347a2abf..2bdb288c11 100644
--- a/src/PhpSpreadsheet/Worksheet/AutoFilter.php
+++ b/src/PhpSpreadsheet/Worksheet/AutoFilter.php
@@ -17,17 +17,13 @@ class AutoFilter
 {
     /**
      * Autofilter Worksheet.
-     *
-     * @var null|Worksheet
      */
-    private $workSheet;
+    private ?Worksheet $workSheet;
 
     /**
      * Autofilter Range.
-     *
-     * @var string
      */
-    private $range = '';
+    private string $range;
 
     /**
      * Autofilter Column Ruleset.
@@ -63,7 +59,7 @@ public function __construct($range = '', ?Worksheet $worksheet = null)
             [, $range] = Worksheet::extractSheetTitle(Validations::validateCellRange($range), true);
         }
 
-        $this->range = $range;
+        $this->range = $range ?? '';
         $this->workSheet = $worksheet;
     }
 
@@ -82,7 +78,7 @@ public function getParent()
      *
      * @return $this
      */
-    public function setParent(?Worksheet $worksheet = null)
+    public function setParent(?Worksheet $worksheet = null): static
     {
         $this->evaluated = false;
         $this->workSheet = $worksheet;
@@ -172,7 +168,7 @@ public function getColumns()
      *
      * @return int The column offset within the autofilter range
      */
-    public function testColumnInRange($column)
+    public function testColumnInRange($column): int
     {
         if (empty($this->range)) {
             throw new Exception('No autofilter range is defined.');
@@ -240,7 +236,7 @@ public function getColumnByOffset($columnOffset)
      *
      * @return $this
      */
-    public function setColumn($columnObjectOrString)
+    public function setColumn($columnObjectOrString): static
     {
         $this->evaluated = false;
         if ((is_string($columnObjectOrString)) && (!empty($columnObjectOrString))) {
@@ -270,7 +266,7 @@ public function setColumn($columnObjectOrString)
      *
      * @return $this
      */
-    public function clearColumn($column)
+    public function clearColumn($column): static
     {
         $this->evaluated = false;
         $this->testColumnInRange($column);
@@ -294,7 +290,7 @@ public function clearColumn($column)
      *
      * @return $this
      */
-    public function shiftColumn($fromColumn, $toColumn)
+    public function shiftColumn($fromColumn, $toColumn): static
     {
         $this->evaluated = false;
         $fromColumn = strtoupper($fromColumn);
@@ -321,7 +317,7 @@ public function shiftColumn($fromColumn, $toColumn)
      *
      * @return bool
      */
-    protected static function filterTestInSimpleDataSet($cellValue, $dataSet)
+    protected static function filterTestInSimpleDataSet($cellValue, array $dataSet)
     {
         $dataSetValues = $dataSet['filterValues'];
         $blanks = $dataSet['blanks'];
@@ -340,7 +336,7 @@ protected static function filterTestInSimpleDataSet($cellValue, $dataSet)
      *
      * @return bool
      */
-    protected static function filterTestInDateGroupSet($cellValue, $dataSet)
+    protected static function filterTestInDateGroupSet($cellValue, array $dataSet)
     {
         $dateSet = $dataSet['filterValues'];
         $blanks = $dataSet['blanks'];
@@ -381,10 +377,8 @@ protected static function filterTestInDateGroupSet($cellValue, $dataSet)
      *
      * @param mixed $cellValue
      * @param mixed[] $ruleSet
-     *
-     * @return bool
      */
-    protected static function filterTestInCustomDataSet($cellValue, $ruleSet)
+    protected static function filterTestInCustomDataSet($cellValue, $ruleSet): bool
     {
         /** @var array[] */
         $dataSet = $ruleSet['filterRules'];
@@ -506,10 +500,8 @@ protected static function filterTestInCustomDataSet($cellValue, $ruleSet)
      *
      * @param mixed $cellValue
      * @param mixed[] $monthSet
-     *
-     * @return bool
      */
-    protected static function filterTestInPeriodDateSet($cellValue, $monthSet)
+    protected static function filterTestInPeriodDateSet($cellValue, $monthSet): bool
     {
         //    Blank cells are always ignored, so return a FALSE
         if (($cellValue == '') || ($cellValue === null)) {
@@ -752,7 +744,7 @@ private static function dynamicYesterday(): array
      *
      * @return mixed[]
      */
-    private function dynamicFilterDateRange($dynamicRuleType, AutoFilter\Column &$filterColumn)
+    private function dynamicFilterDateRange($dynamicRuleType, AutoFilter\Column &$filterColumn): array
     {
         $ruleValues = [];
         $callBack = [__CLASS__, self::DATE_FUNCTIONS[$dynamicRuleType]]; // What if not found?
@@ -779,15 +771,12 @@ private function dynamicFilterDateRange($dynamicRuleType, AutoFilter\Column &$fi
     /**
      * Apply the AutoFilter rules to the AutoFilter Range.
      *
-     * @param string $columnID
-     * @param int $startRow
-     * @param int $endRow
      * @param ?string $ruleType
      * @param mixed $ruleValue
      *
      * @return mixed
      */
-    private function calculateTopTenValue($columnID, $startRow, $endRow, $ruleType, $ruleValue)
+    private function calculateTopTenValue(string $columnID, int $startRow, int $endRow, $ruleType, $ruleValue)
     {
         $range = $columnID . $startRow . ':' . $columnID . $endRow;
         $retVal = null;
@@ -814,7 +803,7 @@ private function calculateTopTenValue($columnID, $startRow, $endRow, $ruleType,
      *
      * @return $this
      */
-    public function showHideRows()
+    public function showHideRows(): static
     {
         if ($this->workSheet === null) {
             return $this;
@@ -947,8 +936,7 @@ public function showHideRows()
                             //    Number (Average) based
                             //    Calculate the average
                             $averageFormula = '=AVERAGE(' . $columnID . ($rangeStart[1] + 1) . ':' . $columnID . $rangeEnd[1] . ')';
-                            $spreadsheet = ($this->workSheet === null) ? null : $this->workSheet->getParent();
-                            $average = Calculation::getInstance($spreadsheet)->calculateFormula($averageFormula, null, $this->workSheet->getCell('A1'));
+                            $average = Calculation::getInstance($this->workSheet->getParent())->calculateFormula($averageFormula, null, $this->workSheet->getCell('A1'));
                             while (is_array($average)) {
                                 $average = array_pop($average);
                             }
@@ -1115,7 +1103,7 @@ public function __clone()
      * toString method replicates previous behavior by returning the range if object is
      * referenced as a property of its parent.
      */
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->range;
     }
diff --git a/src/PhpSpreadsheet/Worksheet/AutoFilter/Column.php b/src/PhpSpreadsheet/Worksheet/AutoFilter/Column.php
index 076292f37a..361ccf045b 100644
--- a/src/PhpSpreadsheet/Worksheet/AutoFilter/Column.php
+++ b/src/PhpSpreadsheet/Worksheet/AutoFilter/Column.php
@@ -48,10 +48,8 @@ class Column
 
     /**
      * Autofilter.
-     *
-     * @var null|AutoFilter
      */
-    private $parent;
+    private ?AutoFilter $parent;
 
     /**
      * Autofilter Column Index.
@@ -124,7 +122,7 @@ public function getColumnIndex()
      *
      * @return $this
      */
-    public function setColumnIndex($column)
+    public function setColumnIndex($column): static
     {
         $this->setEvaluatedFalse();
         // Uppercase coordinate
@@ -153,7 +151,7 @@ public function getParent()
      *
      * @return $this
      */
-    public function setParent(?AutoFilter $parent = null)
+    public function setParent(?AutoFilter $parent = null): static
     {
         $this->setEvaluatedFalse();
         $this->parent = $parent;
@@ -178,7 +176,7 @@ public function getFilterType()
      *
      * @return $this
      */
-    public function setFilterType($filterType)
+    public function setFilterType($filterType): static
     {
         $this->setEvaluatedFalse();
         if (!in_array($filterType, self::$filterTypes)) {
@@ -210,7 +208,7 @@ public function getJoin()
      *
      * @return $this
      */
-    public function setJoin($join)
+    public function setJoin($join): static
     {
         $this->setEvaluatedFalse();
         // Lowercase And/Or
@@ -231,7 +229,7 @@ public function setJoin($join)
      *
      * @return $this
      */
-    public function setAttributes($attributes)
+    public function setAttributes($attributes): static
     {
         $this->setEvaluatedFalse();
         $this->attributes = $attributes;
@@ -247,7 +245,7 @@ public function setAttributes($attributes)
      *
      * @return $this
      */
-    public function setAttribute($name, $value)
+    public function setAttribute($name, $value): static
     {
         $this->setEvaluatedFalse();
         $this->attributes[$name] = $value;
@@ -314,10 +312,8 @@ public function getRule($index)
 
     /**
      * Create a new AutoFilter Column Rule in the ruleset.
-     *
-     * @return Column\Rule
      */
-    public function createRule()
+    public function createRule(): Column\Rule
     {
         $this->setEvaluatedFalse();
         if ($this->filterType === self::AUTOFILTER_FILTERTYPE_CUSTOMFILTER && count($this->ruleset) >= 2) {
@@ -333,7 +329,7 @@ public function createRule()
      *
      * @return $this
      */
-    public function addRule(Column\Rule $rule)
+    public function addRule(Column\Rule $rule): static
     {
         $this->setEvaluatedFalse();
         $rule->setParent($this);
@@ -350,7 +346,7 @@ public function addRule(Column\Rule $rule)
      *
      * @return $this
      */
-    public function deleteRule($index)
+    public function deleteRule($index): static
     {
         $this->setEvaluatedFalse();
         if (isset($this->ruleset[$index])) {
@@ -369,7 +365,7 @@ public function deleteRule($index)
      *
      * @return $this
      */
-    public function clearRules()
+    public function clearRules(): static
     {
         $this->setEvaluatedFalse();
         $this->ruleset = [];
diff --git a/src/PhpSpreadsheet/Worksheet/AutoFilter/Column/Rule.php b/src/PhpSpreadsheet/Worksheet/AutoFilter/Column/Rule.php
index 408dfb3f06..aed9561106 100644
--- a/src/PhpSpreadsheet/Worksheet/AutoFilter/Column/Rule.php
+++ b/src/PhpSpreadsheet/Worksheet/AutoFilter/Column/Rule.php
@@ -169,13 +169,10 @@ class Rule
     // Rule Operators (Date Special) which are translated to standard numeric operators with calculated values
     //    const AUTOFILTER_COLUMN_RULE_BEFORE                = 'lessThan';
     //    const AUTOFILTER_COLUMN_RULE_AFTER                = 'greaterThan';
-
     /**
      * Autofilter Column.
-     *
-     * @var ?Column
      */
-    private $parent;
+    private ?Column $parent;
 
     /**
      * Autofilter Rule Type.
@@ -237,7 +234,7 @@ public function getRuleType()
      *
      * @return $this
      */
-    public function setRuleType($ruleType)
+    public function setRuleType($ruleType): static
     {
         $this->setEvaluatedFalse();
         if (!in_array($ruleType, self::RULE_TYPES)) {
@@ -266,7 +263,7 @@ public function getValue()
      *
      * @return $this
      */
-    public function setValue($value)
+    public function setValue($value): static
     {
         $this->setEvaluatedFalse();
         if (is_array($value)) {
@@ -309,7 +306,7 @@ public function getOperator()
      *
      * @return $this
      */
-    public function setOperator($operator)
+    public function setOperator($operator): static
     {
         $this->setEvaluatedFalse();
         if (empty($operator)) {
@@ -343,7 +340,7 @@ public function getGrouping()
      *
      * @return $this
      */
-    public function setGrouping($grouping)
+    public function setGrouping($grouping): static
     {
         $this->setEvaluatedFalse();
         if (
@@ -368,7 +365,7 @@ public function setGrouping($grouping)
      *
      * @return $this
      */
-    public function setRule($operator, $value, $grouping = null)
+    public function setRule($operator, $value, $grouping = null): static
     {
         $this->setEvaluatedFalse();
         $this->setOperator($operator);
@@ -398,7 +395,7 @@ public function getParent()
      *
      * @return $this
      */
-    public function setParent(?Column $parent = null)
+    public function setParent(?Column $parent = null): static
     {
         $this->setEvaluatedFalse();
         $this->parent = $parent;
diff --git a/src/PhpSpreadsheet/Worksheet/BaseDrawing.php b/src/PhpSpreadsheet/Worksheet/BaseDrawing.php
index 0226e6852b..1d3635ddbc 100644
--- a/src/PhpSpreadsheet/Worksheet/BaseDrawing.php
+++ b/src/PhpSpreadsheet/Worksheet/BaseDrawing.php
@@ -5,6 +5,7 @@
 use PhpOffice\PhpSpreadsheet\Cell\Hyperlink;
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
 use PhpOffice\PhpSpreadsheet\IComparable;
+use PhpOffice\PhpSpreadsheet\Worksheet\Drawing\Shadow;
 use SimpleXMLElement;
 
 class BaseDrawing implements IComparable
@@ -20,10 +21,8 @@ class BaseDrawing implements IComparable
 
     /**
      * The editAs attribute, used only with two cell anchor.
-     *
-     * @var string
      */
-    protected $editAs = '';
+    protected string $editAs = '';
 
     /**
      * Image counter.
@@ -34,38 +33,28 @@ class BaseDrawing implements IComparable
 
     /**
      * Image index.
-     *
-     * @var int
      */
-    private $imageIndex = 0;
+    private int $imageIndex;
 
     /**
      * Name.
-     *
-     * @var string
      */
-    protected $name = '';
+    protected string $name = '';
 
     /**
      * Description.
-     *
-     * @var string
      */
-    protected $description = '';
+    protected string $description = '';
 
     /**
      * Worksheet.
-     *
-     * @var null|Worksheet
      */
-    protected $worksheet;
+    protected ?Worksheet $worksheet = null;
 
     /**
      * Coordinates.
-     *
-     * @var string
      */
-    protected $coordinates = 'A1';
+    protected string $coordinates = 'A1';
 
     /**
      * Offset X.
@@ -83,10 +72,8 @@ class BaseDrawing implements IComparable
 
     /**
      * Coordinates2.
-     *
-     * @var string
      */
-    protected $coordinates2 = '';
+    protected string $coordinates2 = '';
 
     /**
      * Offset X2.
@@ -146,17 +133,13 @@ class BaseDrawing implements IComparable
 
     /**
      * Shadow.
-     *
-     * @var Drawing\Shadow
      */
-    protected $shadow;
+    protected Shadow $shadow;
 
     /**
      * Image hyperlink.
-     *
-     * @var null|Hyperlink
      */
-    private $hyperlink;
+    private ?Hyperlink $hyperlink = null;
 
     /**
      * Image type.
@@ -435,7 +418,7 @@ public function setShadow(?Drawing\Shadow $shadow = null): self
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->name .
diff --git a/src/PhpSpreadsheet/Worksheet/Column.php b/src/PhpSpreadsheet/Worksheet/Column.php
index 077ba5da94..d2bbffb3ac 100644
--- a/src/PhpSpreadsheet/Worksheet/Column.php
+++ b/src/PhpSpreadsheet/Worksheet/Column.php
@@ -4,19 +4,12 @@
 
 class Column
 {
-    /**
-     * \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet.
-     *
-     * @var Worksheet
-     */
-    private $worksheet;
+    private ?Worksheet $worksheet;
 
     /**
      * Column index.
-     *
-     * @var string
      */
-    private $columnIndex;
+    private string $columnIndex;
 
     /**
      * Create a new column.
@@ -35,7 +28,6 @@ public function __construct(Worksheet $worksheet, $columnIndex = 'A')
      */
     public function __destruct()
     {
-        // @phpstan-ignore-next-line
         $this->worksheet = null;
     }
 
@@ -55,7 +47,7 @@ public function getColumnIndex(): string
      */
     public function getCellIterator($startRow = 1, $endRow = null): ColumnCellIterator
     {
-        return new ColumnCellIterator($this->worksheet, $this->columnIndex, $startRow, $endRow);
+        return new ColumnCellIterator($this->getWorksheet(), $this->columnIndex, $startRow, $endRow);
     }
 
     /**
@@ -116,6 +108,7 @@ public function isEmpty(int $definitionOfEmptyFlags = 0, $startRow = 1, $endRow
      */
     public function getWorksheet(): Worksheet
     {
+        // @phpstan-ignore-next-line
         return $this->worksheet;
     }
 }
diff --git a/src/PhpSpreadsheet/Worksheet/ColumnCellIterator.php b/src/PhpSpreadsheet/Worksheet/ColumnCellIterator.php
index ed88d4ecaf..ba9312b499 100644
--- a/src/PhpSpreadsheet/Worksheet/ColumnCellIterator.php
+++ b/src/PhpSpreadsheet/Worksheet/ColumnCellIterator.php
@@ -13,17 +13,13 @@ class ColumnCellIterator extends CellIterator
 {
     /**
      * Current iterator position.
-     *
-     * @var int
      */
-    private $currentRow;
+    private int $currentRow;
 
     /**
      * Column index.
-     *
-     * @var int
      */
-    private $columnIndex;
+    private int $columnIndex;
 
     /**
      * Start position.
@@ -47,7 +43,7 @@ class ColumnCellIterator extends CellIterator
      * @param int $startRow The row number at which to start iterating
      * @param int $endRow Optionally, the row number at which to stop iterating
      */
-    public function __construct(Worksheet $worksheet, $columnIndex = 'A', $startRow = 1, $endRow = null)
+    public function __construct(Worksheet $worksheet, $columnIndex = 'A', int $startRow = 1, $endRow = null)
     {
         // Set subject
         $this->worksheet = $worksheet;
@@ -64,7 +60,7 @@ public function __construct(Worksheet $worksheet, $columnIndex = 'A', $startRow
      *
      * @return $this
      */
-    public function resetStart(int $startRow = 1)
+    public function resetStart(int $startRow = 1): static
     {
         $this->startRow = $startRow;
         $this->adjustForExistingOnlyRange();
@@ -80,7 +76,7 @@ public function resetStart(int $startRow = 1)
      *
      * @return $this
      */
-    public function resetEnd($endRow = null)
+    public function resetEnd($endRow = null): static
     {
         $this->endRow = $endRow ?: $this->worksheet->getHighestRow();
         $this->adjustForExistingOnlyRange();
@@ -95,7 +91,7 @@ public function resetEnd($endRow = null)
      *
      * @return $this
      */
-    public function seek(int $row = 1)
+    public function seek(int $row = 1): static
     {
         if (
             $this->onlyExistingCells &&
diff --git a/src/PhpSpreadsheet/Worksheet/ColumnDimension.php b/src/PhpSpreadsheet/Worksheet/ColumnDimension.php
index 9393648283..07f7413426 100644
--- a/src/PhpSpreadsheet/Worksheet/ColumnDimension.php
+++ b/src/PhpSpreadsheet/Worksheet/ColumnDimension.php
@@ -9,10 +9,8 @@ class ColumnDimension extends Dimension
 {
     /**
      * Column index.
-     *
-     * @var ?string
      */
-    private $columnIndex;
+    private ?string $columnIndex;
 
     /**
      * Column width.
@@ -106,7 +104,7 @@ public function getWidth(?string $unitOfMeasure = null): float
      *
      * @return $this
      */
-    public function setWidth(float $width, ?string $unitOfMeasure = null)
+    public function setWidth(float $width, ?string $unitOfMeasure = null): static
     {
         $this->width = ($unitOfMeasure === null || $width < 0)
             ? $width
@@ -128,7 +126,7 @@ public function getAutoSize(): bool
      *
      * @return $this
      */
-    public function setAutoSize(bool $autosizeEnabled)
+    public function setAutoSize(bool $autosizeEnabled): static
     {
         $this->autoSize = $autosizeEnabled;
 
diff --git a/src/PhpSpreadsheet/Worksheet/ColumnIterator.php b/src/PhpSpreadsheet/Worksheet/ColumnIterator.php
index fffef12928..4910393c3f 100644
--- a/src/PhpSpreadsheet/Worksheet/ColumnIterator.php
+++ b/src/PhpSpreadsheet/Worksheet/ColumnIterator.php
@@ -47,7 +47,7 @@ class ColumnIterator implements NativeIterator
      * @param string $startColumn The column address at which to start iterating
      * @param string $endColumn Optionally, the column address at which to stop iterating
      */
-    public function __construct(Worksheet $worksheet, $startColumn = 'A', $endColumn = null)
+    public function __construct(Worksheet $worksheet, string $startColumn = 'A', $endColumn = null)
     {
         // Set subject
         $this->worksheet = $worksheet;
@@ -71,7 +71,7 @@ public function __destruct()
      *
      * @return $this
      */
-    public function resetStart(string $startColumn = 'A')
+    public function resetStart(string $startColumn = 'A'): static
     {
         $startColumnIndex = Coordinate::columnIndexFromString($startColumn);
         if ($startColumnIndex > Coordinate::columnIndexFromString($this->worksheet->getHighestColumn())) {
@@ -96,7 +96,7 @@ public function resetStart(string $startColumn = 'A')
      *
      * @return $this
      */
-    public function resetEnd($endColumn = null)
+    public function resetEnd($endColumn = null): static
     {
         $endColumn = $endColumn ?: $this->worksheet->getHighestColumn();
         $this->endColumnIndex = Coordinate::columnIndexFromString($endColumn);
@@ -111,7 +111,7 @@ public function resetEnd($endColumn = null)
      *
      * @return $this
      */
-    public function seek(string $column = 'A')
+    public function seek(string $column = 'A'): static
     {
         $column = Coordinate::columnIndexFromString($column);
         if (($column < $this->startColumnIndex) || ($column > $this->endColumnIndex)) {
diff --git a/src/PhpSpreadsheet/Worksheet/Dimension.php b/src/PhpSpreadsheet/Worksheet/Dimension.php
index 7f144063b7..8549b16954 100644
--- a/src/PhpSpreadsheet/Worksheet/Dimension.php
+++ b/src/PhpSpreadsheet/Worksheet/Dimension.php
@@ -29,10 +29,8 @@ abstract class Dimension
 
     /**
      * Index to cellXf. Null value means row has no explicit cellXf format.
-     *
-     * @var null|int
      */
-    private $xfIndex;
+    private ?int $xfIndex;
 
     /**
      * Create a new Dimension.
diff --git a/src/PhpSpreadsheet/Worksheet/Drawing.php b/src/PhpSpreadsheet/Worksheet/Drawing.php
index 7d957539ef..e9c2e80431 100644
--- a/src/PhpSpreadsheet/Worksheet/Drawing.php
+++ b/src/PhpSpreadsheet/Worksheet/Drawing.php
@@ -16,17 +16,13 @@ class Drawing extends BaseDrawing
 
     /**
      * Path.
-     *
-     * @var string
      */
-    private $path;
+    private string $path;
 
     /**
      * Whether or not we are dealing with a URL.
-     *
-     * @var bool
      */
-    private $isUrl;
+    private bool $isUrl;
 
     /**
      * Create a new Drawing.
@@ -43,10 +39,8 @@ public function __construct()
 
     /**
      * Get Filename.
-     *
-     * @return string
      */
-    public function getFilename()
+    public function getFilename(): string
     {
         return basename($this->path);
     }
@@ -61,10 +55,8 @@ public function getIndexedFilename(): string
 
     /**
      * Get Extension.
-     *
-     * @return string
      */
-    public function getExtension()
+    public function getExtension(): string
     {
         $exploded = explode('.', basename($this->path));
 
@@ -73,10 +65,8 @@ public function getExtension()
 
     /**
      * Get full filepath to store drawing in zip archive.
-     *
-     * @return string
      */
-    public function getMediaFilename()
+    public function getMediaFilename(): string
     {
         if (!array_key_exists($this->type, self::IMAGE_TYPES_CONVERTION_MAP)) {
             throw new PhpSpreadsheetException('Unsupported image type in comment background. Supported types: PNG, JPEG, BMP, GIF.');
@@ -104,7 +94,7 @@ public function getPath()
      *
      * @return $this
      */
-    public function setPath($path, $verifyFile = true, $zip = null)
+    public function setPath($path, $verifyFile = true, $zip = null): static
     {
         if ($verifyFile && preg_match('~^data:image/[a-z]+;base64,~', $path) !== 1) {
             // Check if a URL has been passed. https://stackoverflow.com/a/2058596/1252979
@@ -165,7 +155,7 @@ public function setIsURL(bool $isUrl): self
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->path .
diff --git a/src/PhpSpreadsheet/Worksheet/Drawing/Shadow.php b/src/PhpSpreadsheet/Worksheet/Drawing/Shadow.php
index ca396d221d..5e16a9754d 100644
--- a/src/PhpSpreadsheet/Worksheet/Drawing/Shadow.php
+++ b/src/PhpSpreadsheet/Worksheet/Drawing/Shadow.php
@@ -19,56 +19,42 @@ class Shadow implements IComparable
 
     /**
      * Visible.
-     *
-     * @var bool
      */
-    private $visible;
+    private bool $visible;
 
     /**
      * Blur radius.
      *
      * Defaults to 6
-     *
-     * @var int
      */
-    private $blurRadius;
+    private int $blurRadius;
 
     /**
      * Shadow distance.
      *
      * Defaults to 2
-     *
-     * @var int
      */
-    private $distance;
+    private int $distance;
 
     /**
      * Shadow direction (in degrees).
-     *
-     * @var int
      */
-    private $direction;
+    private int $direction;
 
     /**
      * Shadow alignment.
-     *
-     * @var string
      */
-    private $alignment;
+    private string $alignment;
 
     /**
      * Color.
-     *
-     * @var Color
      */
-    private $color;
+    private Color $color;
 
     /**
      * Alpha.
-     *
-     * @var int
      */
-    private $alpha;
+    private int $alpha;
 
     /**
      * Create a new Shadow.
@@ -102,7 +88,7 @@ public function getVisible()
      *
      * @return $this
      */
-    public function setVisible($visible)
+    public function setVisible($visible): static
     {
         $this->visible = $visible;
 
@@ -126,7 +112,7 @@ public function getBlurRadius()
      *
      * @return $this
      */
-    public function setBlurRadius($blurRadius)
+    public function setBlurRadius($blurRadius): static
     {
         $this->blurRadius = $blurRadius;
 
@@ -150,7 +136,7 @@ public function getDistance()
      *
      * @return $this
      */
-    public function setDistance($distance)
+    public function setDistance($distance): static
     {
         $this->distance = $distance;
 
@@ -174,7 +160,7 @@ public function getDirection()
      *
      * @return $this
      */
-    public function setDirection($direction)
+    public function setDirection($direction): static
     {
         $this->direction = $direction;
 
@@ -198,7 +184,7 @@ public function getAlignment()
      *
      * @return $this
      */
-    public function setAlignment($alignment)
+    public function setAlignment($alignment): static
     {
         $this->alignment = $alignment;
 
@@ -220,7 +206,7 @@ public function getColor()
      *
      * @return $this
      */
-    public function setColor(Color $color)
+    public function setColor(Color $color): static
     {
         $this->color = $color;
 
@@ -244,7 +230,7 @@ public function getAlpha()
      *
      * @return $this
      */
-    public function setAlpha($alpha)
+    public function setAlpha($alpha): static
     {
         $this->alpha = $alpha;
 
@@ -256,7 +242,7 @@ public function setAlpha($alpha)
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             ($this->visible ? 't' : 'f') .
diff --git a/src/PhpSpreadsheet/Worksheet/HeaderFooter.php b/src/PhpSpreadsheet/Worksheet/HeaderFooter.php
index c3504d831b..5772afc608 100644
--- a/src/PhpSpreadsheet/Worksheet/HeaderFooter.php
+++ b/src/PhpSpreadsheet/Worksheet/HeaderFooter.php
@@ -174,7 +174,7 @@ public function getOddHeader()
      *
      * @return $this
      */
-    public function setOddHeader($oddHeader)
+    public function setOddHeader($oddHeader): static
     {
         $this->oddHeader = $oddHeader;
 
@@ -198,7 +198,7 @@ public function getOddFooter()
      *
      * @return $this
      */
-    public function setOddFooter($oddFooter)
+    public function setOddFooter($oddFooter): static
     {
         $this->oddFooter = $oddFooter;
 
@@ -222,7 +222,7 @@ public function getEvenHeader()
      *
      * @return $this
      */
-    public function setEvenHeader($eventHeader)
+    public function setEvenHeader($eventHeader): static
     {
         $this->evenHeader = $eventHeader;
 
@@ -246,7 +246,7 @@ public function getEvenFooter()
      *
      * @return $this
      */
-    public function setEvenFooter($evenFooter)
+    public function setEvenFooter($evenFooter): static
     {
         $this->evenFooter = $evenFooter;
 
@@ -270,7 +270,7 @@ public function getFirstHeader()
      *
      * @return $this
      */
-    public function setFirstHeader($firstHeader)
+    public function setFirstHeader($firstHeader): static
     {
         $this->firstHeader = $firstHeader;
 
@@ -294,7 +294,7 @@ public function getFirstFooter()
      *
      * @return $this
      */
-    public function setFirstFooter($firstFooter)
+    public function setFirstFooter($firstFooter): static
     {
         $this->firstFooter = $firstFooter;
 
@@ -318,7 +318,7 @@ public function getDifferentOddEven()
      *
      * @return $this
      */
-    public function setDifferentOddEven($differentOddEvent)
+    public function setDifferentOddEven($differentOddEvent): static
     {
         $this->differentOddEven = $differentOddEvent;
 
@@ -342,7 +342,7 @@ public function getDifferentFirst()
      *
      * @return $this
      */
-    public function setDifferentFirst($differentFirst)
+    public function setDifferentFirst($differentFirst): static
     {
         $this->differentFirst = $differentFirst;
 
@@ -366,7 +366,7 @@ public function getScaleWithDocument()
      *
      * @return $this
      */
-    public function setScaleWithDocument($scaleWithDocument)
+    public function setScaleWithDocument($scaleWithDocument): static
     {
         $this->scaleWithDocument = $scaleWithDocument;
 
@@ -390,7 +390,7 @@ public function getAlignWithMargins()
      *
      * @return $this
      */
-    public function setAlignWithMargins($alignWithMargins)
+    public function setAlignWithMargins($alignWithMargins): static
     {
         $this->alignWithMargins = $alignWithMargins;
 
@@ -404,7 +404,7 @@ public function setAlignWithMargins($alignWithMargins)
      *
      * @return $this
      */
-    public function addImage(HeaderFooterDrawing $image, $location = self::IMAGE_HEADER_LEFT)
+    public function addImage(HeaderFooterDrawing $image, $location = self::IMAGE_HEADER_LEFT): static
     {
         $this->headerFooterImages[$location] = $image;
 
@@ -418,7 +418,7 @@ public function addImage(HeaderFooterDrawing $image, $location = self::IMAGE_HEA
      *
      * @return $this
      */
-    public function removeImage($location = self::IMAGE_HEADER_LEFT)
+    public function removeImage($location = self::IMAGE_HEADER_LEFT): static
     {
         if (isset($this->headerFooterImages[$location])) {
             unset($this->headerFooterImages[$location]);
@@ -434,7 +434,7 @@ public function removeImage($location = self::IMAGE_HEADER_LEFT)
      *
      * @return $this
      */
-    public function setImages(array $images)
+    public function setImages(array $images): static
     {
         $this->headerFooterImages = $images;
 
@@ -446,7 +446,7 @@ public function setImages(array $images)
      *
      * @return HeaderFooterDrawing[]
      */
-    public function getImages()
+    public function getImages(): array
     {
         // Sort array
         $images = [];
diff --git a/src/PhpSpreadsheet/Worksheet/HeaderFooterDrawing.php b/src/PhpSpreadsheet/Worksheet/HeaderFooterDrawing.php
index b42c7324c1..67a270f293 100644
--- a/src/PhpSpreadsheet/Worksheet/HeaderFooterDrawing.php
+++ b/src/PhpSpreadsheet/Worksheet/HeaderFooterDrawing.php
@@ -9,7 +9,7 @@ class HeaderFooterDrawing extends Drawing
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->getPath() .
diff --git a/src/PhpSpreadsheet/Worksheet/Iterator.php b/src/PhpSpreadsheet/Worksheet/Iterator.php
index dc082043e4..a56404642d 100644
--- a/src/PhpSpreadsheet/Worksheet/Iterator.php
+++ b/src/PhpSpreadsheet/Worksheet/Iterator.php
@@ -11,10 +11,8 @@ class Iterator implements \Iterator
 {
     /**
      * Spreadsheet to iterate.
-     *
-     * @var Spreadsheet
      */
-    private $subject;
+    private Spreadsheet $subject;
 
     /**
      * Current iterator position.
diff --git a/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php b/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php
index cf616eb751..c1dc3da21f 100644
--- a/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php
+++ b/src/PhpSpreadsheet/Worksheet/MemoryDrawing.php
@@ -28,34 +28,23 @@ class MemoryDrawing extends BaseDrawing
 
     /**
      * Image resource.
-     *
-     * @var null|GdImage|resource
      */
-    private $imageResource;
+    private null|GdImage $imageResource = null;
 
     /**
      * Rendering function.
-     *
-     * @var string
      */
-    private $renderingFunction;
+    private string $renderingFunction;
 
     /**
      * Mime type.
-     *
-     * @var string
      */
-    private $mimeType;
+    private string $mimeType;
 
     /**
      * Unique name.
-     *
-     * @var string
      */
-    private $uniqueName;
-
-    /** @var null|resource */
-    private $alwaysNull;
+    private string $uniqueName;
 
     /**
      * Create a new MemoryDrawing.
@@ -66,7 +55,6 @@ public function __construct()
         $this->renderingFunction = self::RENDERING_DEFAULT;
         $this->mimeType = self::MIMETYPE_DEFAULT;
         $this->uniqueName = md5(mt_rand(0, 9999) . time() . mt_rand(0, 9999));
-        $this->alwaysNull = null;
 
         // Initialize parent
         parent::__construct();
@@ -75,9 +63,8 @@ public function __construct()
     public function __destruct()
     {
         if ($this->imageResource) {
-            $rslt = @imagedestroy($this->imageResource);
-            // "Fix" for Scrutinizer
-            $this->imageResource = $rslt ? null : $this->alwaysNull;
+            @imagedestroy($this->imageResource);
+            $this->imageResource = null;
         }
     }
 
@@ -253,10 +240,8 @@ private static function supportedMimeTypes(?string $mimeType = null): ?string
 
     /**
      * Get image resource.
-     *
-     * @return null|GdImage|resource
      */
-    public function getImageResource()
+    public function getImageResource(): ?GdImage
     {
         return $this->imageResource;
     }
@@ -264,11 +249,9 @@ public function getImageResource()
     /**
      * Set image resource.
      *
-     * @param GdImage|resource $value
-     *
      * @return $this
      */
-    public function setImageResource($value)
+    public function setImageResource(?GdImage $value): static
     {
         $this->imageResource = $value;
 
@@ -298,7 +281,7 @@ public function getRenderingFunction()
      *
      * @return $this
      */
-    public function setRenderingFunction($value)
+    public function setRenderingFunction($value): static
     {
         $this->renderingFunction = $value;
 
@@ -322,7 +305,7 @@ public function getMimeType()
      *
      * @return $this
      */
-    public function setMimeType($value)
+    public function setMimeType($value): static
     {
         $this->mimeType = $value;
 
@@ -346,7 +329,7 @@ public function getIndexedFilename(): string
      *
      * @return string Hash code
      */
-    public function getHashCode()
+    public function getHashCode(): string
     {
         return md5(
             $this->renderingFunction .
diff --git a/src/PhpSpreadsheet/Worksheet/PageBreak.php b/src/PhpSpreadsheet/Worksheet/PageBreak.php
index 743cc58d69..5099d8be0d 100644
--- a/src/PhpSpreadsheet/Worksheet/PageBreak.php
+++ b/src/PhpSpreadsheet/Worksheet/PageBreak.php
@@ -8,14 +8,11 @@
 
 class PageBreak
 {
-    /** @var int */
-    private $breakType;
+    private int $breakType;
 
-    /** @var string */
-    private $coordinate;
+    private string $coordinate;
 
-    /** @var int */
-    private $maxColOrRow;
+    private int $maxColOrRow;
 
     /** @param array|CellAddress|string $coordinate */
     public function __construct(int $breakType, $coordinate, int $maxColOrRow = -1)
diff --git a/src/PhpSpreadsheet/Worksheet/PageMargins.php b/src/PhpSpreadsheet/Worksheet/PageMargins.php
index d51023fcc1..8039cc3303 100644
--- a/src/PhpSpreadsheet/Worksheet/PageMargins.php
+++ b/src/PhpSpreadsheet/Worksheet/PageMargins.php
@@ -70,7 +70,7 @@ public function getLeft()
      *
      * @return $this
      */
-    public function setLeft($left)
+    public function setLeft($left): static
     {
         $this->left = $left;
 
@@ -94,7 +94,7 @@ public function getRight()
      *
      * @return $this
      */
-    public function setRight($right)
+    public function setRight($right): static
     {
         $this->right = $right;
 
@@ -118,7 +118,7 @@ public function getTop()
      *
      * @return $this
      */
-    public function setTop($top)
+    public function setTop($top): static
     {
         $this->top = $top;
 
@@ -142,7 +142,7 @@ public function getBottom()
      *
      * @return $this
      */
-    public function setBottom($bottom)
+    public function setBottom($bottom): static
     {
         $this->bottom = $bottom;
 
@@ -166,7 +166,7 @@ public function getHeader()
      *
      * @return $this
      */
-    public function setHeader($header)
+    public function setHeader($header): static
     {
         $this->header = $header;
 
@@ -190,7 +190,7 @@ public function getFooter()
      *
      * @return $this
      */
-    public function setFooter($footer)
+    public function setFooter($footer): static
     {
         $this->footer = $footer;
 
diff --git a/src/PhpSpreadsheet/Worksheet/PageSetup.php b/src/PhpSpreadsheet/Worksheet/PageSetup.php
index 72c8958c8b..96987bbe8e 100644
--- a/src/PhpSpreadsheet/Worksheet/PageSetup.php
+++ b/src/PhpSpreadsheet/Worksheet/PageSetup.php
@@ -291,7 +291,7 @@ public function getPaperSize()
      *
      * @return $this
      */
-    public function setPaperSize($paperSize)
+    public function setPaperSize($paperSize): static
     {
         $this->paperSize = $paperSize;
 
@@ -331,7 +331,7 @@ public function getOrientation()
      *
      * @return $this
      */
-    public function setOrientation($orientation)
+    public function setOrientation($orientation): static
     {
         if ($orientation === self::ORIENTATION_LANDSCAPE || $orientation === self::ORIENTATION_PORTRAIT || $orientation === self::ORIENTATION_DEFAULT) {
             $this->orientation = $orientation;
@@ -372,7 +372,7 @@ public function getScale()
      *
      * @return $this
      */
-    public function setScale($scale, $update = true)
+    public function setScale($scale, $update = true): static
     {
         // Microsoft Office Excel 2007 only allows setting a scale between 10 and 400 via the user interface,
         // but it is apparently still able to handle any scale >= 0, where 0 results in 100
@@ -405,7 +405,7 @@ public function getFitToPage()
      *
      * @return $this
      */
-    public function setFitToPage($fitToPage)
+    public function setFitToPage($fitToPage): static
     {
         $this->fitToPage = $fitToPage;
 
@@ -430,7 +430,7 @@ public function getFitToHeight()
      *
      * @return $this
      */
-    public function setFitToHeight($fitToHeight, $update = true)
+    public function setFitToHeight($fitToHeight, $update = true): static
     {
         $this->fitToHeight = $fitToHeight;
         if ($update) {
@@ -458,7 +458,7 @@ public function getFitToWidth()
      *
      * @return $this
      */
-    public function setFitToWidth($value, $update = true)
+    public function setFitToWidth($value, $update = true): static
     {
         $this->fitToWidth = $value;
         if ($update) {
@@ -470,10 +470,8 @@ public function setFitToWidth($value, $update = true)
 
     /**
      * Is Columns to repeat at left set?
-     *
-     * @return bool
      */
-    public function isColumnsToRepeatAtLeftSet()
+    public function isColumnsToRepeatAtLeftSet(): bool
     {
         if (!empty($this->columnsToRepeatAtLeft)) {
             if ($this->columnsToRepeatAtLeft[0] != '' && $this->columnsToRepeatAtLeft[1] != '') {
@@ -501,7 +499,7 @@ public function getColumnsToRepeatAtLeft()
      *
      * @return $this
      */
-    public function setColumnsToRepeatAtLeft(array $columnsToRepeatAtLeft)
+    public function setColumnsToRepeatAtLeft(array $columnsToRepeatAtLeft): static
     {
         $this->columnsToRepeatAtLeft = $columnsToRepeatAtLeft;
 
@@ -516,7 +514,7 @@ public function setColumnsToRepeatAtLeft(array $columnsToRepeatAtLeft)
      *
      * @return $this
      */
-    public function setColumnsToRepeatAtLeftByStartAndEnd($start, $end)
+    public function setColumnsToRepeatAtLeftByStartAndEnd($start, $end): static
     {
         $this->columnsToRepeatAtLeft = [$start, $end];
 
@@ -525,10 +523,8 @@ public function setColumnsToRepeatAtLeftByStartAndEnd($start, $end)
 
     /**
      * Is Rows to repeat at top set?
-     *
-     * @return bool
      */
-    public function isRowsToRepeatAtTopSet()
+    public function isRowsToRepeatAtTopSet(): bool
     {
         if (!empty($this->rowsToRepeatAtTop)) {
             if ($this->rowsToRepeatAtTop[0] != 0 && $this->rowsToRepeatAtTop[1] != 0) {
@@ -556,7 +552,7 @@ public function getRowsToRepeatAtTop()
      *
      * @return $this
      */
-    public function setRowsToRepeatAtTop(array $rowsToRepeatAtTop)
+    public function setRowsToRepeatAtTop(array $rowsToRepeatAtTop): static
     {
         $this->rowsToRepeatAtTop = $rowsToRepeatAtTop;
 
@@ -571,7 +567,7 @@ public function setRowsToRepeatAtTop(array $rowsToRepeatAtTop)
      *
      * @return $this
      */
-    public function setRowsToRepeatAtTopByStartAndEnd($start, $end)
+    public function setRowsToRepeatAtTopByStartAndEnd($start, $end): static
     {
         $this->rowsToRepeatAtTop = [$start, $end];
 
@@ -595,7 +591,7 @@ public function getHorizontalCentered()
      *
      * @return $this
      */
-    public function setHorizontalCentered($value)
+    public function setHorizontalCentered($value): static
     {
         $this->horizontalCentered = $value;
 
@@ -619,7 +615,7 @@ public function getVerticalCentered()
      *
      * @return $this
      */
-    public function setVerticalCentered($value)
+    public function setVerticalCentered($value): static
     {
         $this->verticalCentered = $value;
 
@@ -656,10 +652,8 @@ public function getPrintArea($index = 0)
      *                            Default behaviour, or an index value of 0, will identify whether any print range is set
      *                            Otherwise, existence of the range identified by the value of $index will be returned
      *                            Print areas are numbered from 1
-     *
-     * @return bool
      */
-    public function isPrintAreaSet($index = 0)
+    public function isPrintAreaSet($index = 0): bool
     {
         if ($index == 0) {
             return $this->printArea !== null;
@@ -679,7 +673,7 @@ public function isPrintAreaSet($index = 0)
      *
      * @return $this
      */
-    public function clearPrintArea($index = 0)
+    public function clearPrintArea($index = 0): static
     {
         if ($index == 0) {
             $this->printArea = null;
@@ -714,7 +708,7 @@ public function clearPrintArea($index = 0)
      *
      * @return $this
      */
-    public function setPrintArea($value, $index = 0, $method = self::SETPRINTRANGE_OVERWRITE)
+    public function setPrintArea($value, $index = 0, $method = self::SETPRINTRANGE_OVERWRITE): static
     {
         if (strpos($value, '!') !== false) {
             throw new PhpSpreadsheetException('Cell coordinate must not specify a worksheet.');
@@ -776,7 +770,7 @@ public function setPrintArea($value, $index = 0, $method = self::SETPRINTRANGE_O
      *
      * @return $this
      */
-    public function addPrintArea($value, $index = -1)
+    public function addPrintArea($value, $index = -1): static
     {
         return $this->setPrintArea($value, $index, self::SETPRINTRANGE_INSERT);
     }
@@ -804,7 +798,7 @@ public function addPrintArea($value, $index = -1)
      *
      * @return $this
      */
-    public function setPrintAreaByColumnAndRow($column1, $row1, $column2, $row2, $index = 0, $method = self::SETPRINTRANGE_OVERWRITE)
+    public function setPrintAreaByColumnAndRow($column1, $row1, $column2, $row2, $index = 0, $method = self::SETPRINTRANGE_OVERWRITE): static
     {
         return $this->setPrintArea(
             Coordinate::stringFromColumnIndex($column1) . $row1 . ':' . Coordinate::stringFromColumnIndex($column2) . $row2,
@@ -829,7 +823,7 @@ public function setPrintAreaByColumnAndRow($column1, $row1, $column2, $row2, $in
      *
      * @return $this
      */
-    public function addPrintAreaByColumnAndRow($column1, $row1, $column2, $row2, $index = -1)
+    public function addPrintAreaByColumnAndRow($column1, $row1, $column2, $row2, $index = -1): static
     {
         return $this->setPrintArea(
             Coordinate::stringFromColumnIndex($column1) . $row1 . ':' . Coordinate::stringFromColumnIndex($column2) . $row2,
@@ -855,7 +849,7 @@ public function getFirstPageNumber()
      *
      * @return $this
      */
-    public function setFirstPageNumber($value)
+    public function setFirstPageNumber($value): static
     {
         $this->firstPageNumber = $value;
 
@@ -867,7 +861,7 @@ public function setFirstPageNumber($value)
      *
      * @return $this
      */
-    public function resetFirstPageNumber()
+    public function resetFirstPageNumber(): static
     {
         return $this->setFirstPageNumber(null);
     }
diff --git a/src/PhpSpreadsheet/Worksheet/Protection.php b/src/PhpSpreadsheet/Worksheet/Protection.php
index 063a5cc2be..958a18dc6c 100644
--- a/src/PhpSpreadsheet/Worksheet/Protection.php
+++ b/src/PhpSpreadsheet/Worksheet/Protection.php
@@ -19,115 +19,83 @@ class Protection
 
     /**
      * Autofilters are locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $autoFilter;
+    private ?bool $autoFilter = null;
 
     /**
      * Deleting columns is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $deleteColumns;
+    private ?bool $deleteColumns = null;
 
     /**
      * Deleting rows is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $deleteRows;
+    private ?bool $deleteRows = null;
 
     /**
      * Formatting cells is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $formatCells;
+    private ?bool $formatCells = null;
 
     /**
      * Formatting columns is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $formatColumns;
+    private ?bool $formatColumns = null;
 
     /**
      * Formatting rows is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $formatRows;
+    private ?bool $formatRows = null;
 
     /**
      * Inserting columns is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $insertColumns;
+    private ?bool $insertColumns = null;
 
     /**
      * Inserting hyperlinks is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $insertHyperlinks;
+    private ?bool $insertHyperlinks = null;
 
     /**
      * Inserting rows is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $insertRows;
+    private ?bool $insertRows = null;
 
     /**
      * Objects are locked when sheet is protected, default false.
-     *
-     * @var ?bool
      */
-    private $objects;
+    private ?bool $objects = null;
 
     /**
      * Pivot tables are locked when the sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $pivotTables;
+    private ?bool $pivotTables = null;
 
     /**
      * Scenarios are locked when sheet is protected, default false.
-     *
-     * @var ?bool
      */
-    private $scenarios;
+    private ?bool $scenarios = null;
 
     /**
      * Selection of locked cells is locked when sheet is protected, default false.
-     *
-     * @var ?bool
      */
-    private $selectLockedCells;
+    private ?bool $selectLockedCells = null;
 
     /**
      * Selection of unlocked cells is locked when sheet is protected, default false.
-     *
-     * @var ?bool
      */
-    private $selectUnlockedCells;
+    private ?bool $selectUnlockedCells = null;
 
     /**
      * Sheet is locked when sheet is protected, default false.
-     *
-     * @var ?bool
      */
-    private $sheet;
+    private ?bool $sheet = null;
 
     /**
      * Sorting is locked when sheet is protected, default true.
-     *
-     * @var ?bool
      */
-    private $sort;
+    private ?bool $sort = null;
 
     /**
      * Hashed password.
@@ -138,17 +106,13 @@ class Protection
 
     /**
      * Algorithm name.
-     *
-     * @var string
      */
-    private $algorithm = '';
+    private string $algorithm = '';
 
     /**
      * Salt value.
-     *
-     * @var string
      */
-    private $salt = '';
+    private string $salt = '';
 
     /**
      * Spin count.
@@ -399,7 +363,7 @@ public function getPassword()
      *
      * @return $this
      */
-    public function setPassword($password, $alreadyHashed = false)
+    public function setPassword($password, $alreadyHashed = false): static
     {
         if (!$alreadyHashed) {
             $salt = $this->generateSalt();
diff --git a/src/PhpSpreadsheet/Worksheet/Row.php b/src/PhpSpreadsheet/Worksheet/Row.php
index b5f08816b8..4d8ad57e38 100644
--- a/src/PhpSpreadsheet/Worksheet/Row.php
+++ b/src/PhpSpreadsheet/Worksheet/Row.php
@@ -4,12 +4,7 @@
 
 class Row
 {
-    /**
-     * \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet.
-     *
-     * @var Worksheet
-     */
-    private $worksheet;
+    private ?Worksheet $worksheet;
 
     /**
      * Row index.
@@ -35,7 +30,7 @@ public function __construct(Worksheet $worksheet, $rowIndex = 1)
      */
     public function __destruct()
     {
-        $this->worksheet = null; // @phpstan-ignore-line
+        $this->worksheet = null;
     }
 
     /**
@@ -54,7 +49,7 @@ public function getRowIndex(): int
      */
     public function getCellIterator($startColumn = 'A', $endColumn = null): RowCellIterator
     {
-        return new RowCellIterator($this->worksheet, $this->rowIndex, $startColumn, $endColumn);
+        return new RowCellIterator($this->getWorksheet(), $this->rowIndex, $startColumn, $endColumn);
     }
 
     /**
@@ -115,6 +110,7 @@ public function isEmpty(int $definitionOfEmptyFlags = 0, $startColumn = 'A', $en
      */
     public function getWorksheet(): Worksheet
     {
+        // @phpstan-ignore-next-line
         return $this->worksheet;
     }
 }
diff --git a/src/PhpSpreadsheet/Worksheet/RowCellIterator.php b/src/PhpSpreadsheet/Worksheet/RowCellIterator.php
index 0df776f2af..4174fd2230 100644
--- a/src/PhpSpreadsheet/Worksheet/RowCellIterator.php
+++ b/src/PhpSpreadsheet/Worksheet/RowCellIterator.php
@@ -13,10 +13,8 @@ class RowCellIterator extends CellIterator
 {
     /**
      * Current iterator position.
-     *
-     * @var int
      */
-    private $currentColumnIndex;
+    private int $currentColumnIndex;
 
     /**
      * Row index.
@@ -47,7 +45,7 @@ class RowCellIterator extends CellIterator
      * @param string $startColumn The column address at which to start iterating
      * @param string $endColumn Optionally, the column address at which to stop iterating
      */
-    public function __construct(Worksheet $worksheet, $rowIndex = 1, $startColumn = 'A', $endColumn = null)
+    public function __construct(Worksheet $worksheet, $rowIndex = 1, string $startColumn = 'A', $endColumn = null)
     {
         // Set subject and row index
         $this->worksheet = $worksheet;
@@ -64,7 +62,7 @@ public function __construct(Worksheet $worksheet, $rowIndex = 1, $startColumn =
      *
      * @return $this
      */
-    public function resetStart(string $startColumn = 'A')
+    public function resetStart(string $startColumn = 'A'): static
     {
         $this->startColumnIndex = Coordinate::columnIndexFromString($startColumn);
         $this->adjustForExistingOnlyRange();
@@ -80,7 +78,7 @@ public function resetStart(string $startColumn = 'A')
      *
      * @return $this
      */
-    public function resetEnd($endColumn = null)
+    public function resetEnd($endColumn = null): static
     {
         $endColumn = $endColumn ?: $this->worksheet->getHighestColumn();
         $this->endColumnIndex = Coordinate::columnIndexFromString($endColumn);
@@ -96,7 +94,7 @@ public function resetEnd($endColumn = null)
      *
      * @return $this
      */
-    public function seek(string $column = 'A')
+    public function seek(string $column = 'A'): static
     {
         $columnId = Coordinate::columnIndexFromString($column);
         if ($this->onlyExistingCells && !($this->cellCollection->has($column . $this->rowIndex))) {
diff --git a/src/PhpSpreadsheet/Worksheet/RowDimension.php b/src/PhpSpreadsheet/Worksheet/RowDimension.php
index a5e0f98b79..b3c213a96b 100644
--- a/src/PhpSpreadsheet/Worksheet/RowDimension.php
+++ b/src/PhpSpreadsheet/Worksheet/RowDimension.php
@@ -8,10 +8,8 @@ class RowDimension extends Dimension
 {
     /**
      * Row index.
-     *
-     * @var ?int
      */
-    private $rowIndex;
+    private ?int $rowIndex;
 
     /**
      * Row height (in pt).
@@ -56,7 +54,7 @@ public function getRowIndex(): ?int
      *
      * @return $this
      */
-    public function setRowIndex(int $index)
+    public function setRowIndex(int $index): static
     {
         $this->rowIndex = $index;
 
@@ -87,7 +85,7 @@ public function getRowHeight(?string $unitOfMeasure = null)
      *
      * @return $this
      */
-    public function setRowHeight($height, ?string $unitOfMeasure = null)
+    public function setRowHeight($height, ?string $unitOfMeasure = null): static
     {
         $this->height = ($unitOfMeasure === null || $height < 0)
             ? $height
@@ -109,7 +107,7 @@ public function getZeroHeight(): bool
      *
      * @return $this
      */
-    public function setZeroHeight(bool $zeroHeight)
+    public function setZeroHeight(bool $zeroHeight): static
     {
         $this->zeroHeight = $zeroHeight;
 
diff --git a/src/PhpSpreadsheet/Worksheet/RowIterator.php b/src/PhpSpreadsheet/Worksheet/RowIterator.php
index af2bda25a6..27723d9dd6 100644
--- a/src/PhpSpreadsheet/Worksheet/RowIterator.php
+++ b/src/PhpSpreadsheet/Worksheet/RowIterator.php
@@ -45,7 +45,7 @@ class RowIterator implements NativeIterator
      * @param int $startRow The row number at which to start iterating
      * @param int $endRow Optionally, the row number at which to stop iterating
      */
-    public function __construct(Worksheet $subject, $startRow = 1, $endRow = null)
+    public function __construct(Worksheet $subject, int $startRow = 1, $endRow = null)
     {
         // Set subject
         $this->subject = $subject;
@@ -65,7 +65,7 @@ public function __destruct()
      *
      * @return $this
      */
-    public function resetStart(int $startRow = 1)
+    public function resetStart(int $startRow = 1): static
     {
         if ($startRow > $this->subject->getHighestRow()) {
             throw new PhpSpreadsheetException(
@@ -89,7 +89,7 @@ public function resetStart(int $startRow = 1)
      *
      * @return $this
      */
-    public function resetEnd($endRow = null)
+    public function resetEnd($endRow = null): static
     {
         $this->endRow = $endRow ?: $this->subject->getHighestRow();
 
@@ -103,7 +103,7 @@ public function resetEnd($endRow = null)
      *
      * @return $this
      */
-    public function seek(int $row = 1)
+    public function seek(int $row = 1): static
     {
         if (($row < $this->startRow) || ($row > $this->endRow)) {
             throw new PhpSpreadsheetException("Row $row is out of range ({$this->startRow} - {$this->endRow})");
diff --git a/src/PhpSpreadsheet/Worksheet/SheetView.php b/src/PhpSpreadsheet/Worksheet/SheetView.php
index 697f11c2ae..f61fe6a690 100644
--- a/src/PhpSpreadsheet/Worksheet/SheetView.php
+++ b/src/PhpSpreadsheet/Worksheet/SheetView.php
@@ -79,7 +79,7 @@ public function getZoomScale()
      *
      * @return $this
      */
-    public function setZoomScale($zoomScale)
+    public function setZoomScale($zoomScale): static
     {
         // Microsoft Office Excel 2007 only allows setting a scale between 10 and 400 via the user interface,
         // but it is apparently still able to handle any scale >= 1
@@ -110,7 +110,7 @@ public function getZoomScaleNormal()
      *
      * @return $this
      */
-    public function setZoomScaleNormal($zoomScaleNormal)
+    public function setZoomScaleNormal($zoomScaleNormal): static
     {
         if ($zoomScaleNormal === null || $zoomScaleNormal >= 1) {
             $this->zoomScaleNormal = $zoomScaleNormal;
@@ -161,7 +161,7 @@ public function getView()
      *
      * @return $this
      */
-    public function setView($sheetViewType)
+    public function setView($sheetViewType): static
     {
         // MS Excel 2007 allows setting the view to 'normal', 'pageLayout' or 'pageBreakPreview' via the user interface
         if ($sheetViewType === null) {
diff --git a/src/PhpSpreadsheet/Worksheet/Table.php b/src/PhpSpreadsheet/Worksheet/Table.php
index af70024fba..9a48632d03 100644
--- a/src/PhpSpreadsheet/Worksheet/Table.php
+++ b/src/PhpSpreadsheet/Worksheet/Table.php
@@ -14,10 +14,8 @@ class Table
 {
     /**
      * Table Name.
-     *
-     * @var string
      */
-    private $name;
+    private string $name;
 
     /**
      * Show Header Row.
@@ -35,17 +33,13 @@ class Table
 
     /**
      * Table Range.
-     *
-     * @var string
      */
-    private $range = '';
+    private string $range = '';
 
     /**
      * Table Worksheet.
-     *
-     * @var null|Worksheet
      */
-    private $workSheet;
+    private ?Worksheet $workSheet = null;
 
     /**
      * Table allow filter.
@@ -63,17 +57,13 @@ class Table
 
     /**
      * Table Style.
-     *
-     * @var TableStyle
      */
-    private $style;
+    private TableStyle $style;
 
     /**
      * Table AutoFilter.
-     *
-     * @var AutoFilter
      */
-    private $autoFilter;
+    private AutoFilter $autoFilter;
 
     /**
      * Create a new Table.
@@ -170,7 +160,7 @@ private function checkForDuplicateTableNames(string $name, ?Worksheet $worksheet
 
     private function updateStructuredReferences(string $name): void
     {
-        if ($this->workSheet === null || $this->name === null || $this->name === '') {
+        if (!$this->workSheet || !$this->name) {
             return;
         }
 
@@ -412,7 +402,7 @@ public function isColumnInRange(string $column): int
      *
      * @return int The offset of the specified column within the table range
      */
-    public function getColumnOffset($column): int
+    public function getColumnOffset(string $column): int
     {
         return $this->isColumnInRange($column);
     }
@@ -586,7 +576,7 @@ public function __clone()
      * toString method replicates previous behavior by returning the range if object is
      * referenced as a property of its worksheet.
      */
-    public function __toString()
+    public function __toString(): string
     {
         return (string) $this->range;
     }
diff --git a/src/PhpSpreadsheet/Worksheet/Table/Column.php b/src/PhpSpreadsheet/Worksheet/Table/Column.php
index 32dd4c4f83..f697423894 100644
--- a/src/PhpSpreadsheet/Worksheet/Table/Column.php
+++ b/src/PhpSpreadsheet/Worksheet/Table/Column.php
@@ -12,10 +12,8 @@ class Column
 {
     /**
      * Table Column Index.
-     *
-     * @var string
      */
-    private $columnIndex = '';
+    private string $columnIndex = '';
 
     /**
      * Show Filter Button.
@@ -26,38 +24,28 @@ class Column
 
     /**
      * Total Row Label.
-     *
-     * @var string
      */
-    private $totalsRowLabel;
+    private ?string $totalsRowLabel = null;
 
     /**
      * Total Row Function.
-     *
-     * @var string
      */
-    private $totalsRowFunction;
+    private ?string $totalsRowFunction = null;
 
     /**
      * Total Row Formula.
-     *
-     * @var string
      */
-    private $totalsRowFormula;
+    private ?string $totalsRowFormula = null;
 
     /**
      * Column Formula.
-     *
-     * @var string
      */
-    private $columnFormula;
+    private ?string $columnFormula = null;
 
     /**
      * Table.
-     *
-     * @var null|Table
      */
-    private $table;
+    private ?Table $table;
 
     /**
      * Create a new Column.
diff --git a/src/PhpSpreadsheet/Worksheet/Table/TableStyle.php b/src/PhpSpreadsheet/Worksheet/Table/TableStyle.php
index 78643c729e..c0744c995b 100644
--- a/src/PhpSpreadsheet/Worksheet/Table/TableStyle.php
+++ b/src/PhpSpreadsheet/Worksheet/Table/TableStyle.php
@@ -70,10 +70,8 @@ class TableStyle
 
     /**
      * Theme.
-     *
-     * @var string
      */
-    private $theme;
+    private string $theme;
 
     /**
      * Show First Column.
@@ -105,10 +103,8 @@ class TableStyle
 
     /**
      * Table.
-     *
-     * @var null|Table
      */
-    private $table;
+    private ?Table $table = null;
 
     /**
      * Create a new Table Style.
diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index a904c8f62b..1a20a9ec44 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -67,17 +67,13 @@ class Worksheet implements IComparable
 
     /**
      * Parent spreadsheet.
-     *
-     * @var ?Spreadsheet
      */
-    private $parent;
+    private ?Spreadsheet $parent;
 
     /**
      * Collection of cells.
-     *
-     * @var Cells
      */
-    private $cellCollection;
+    private ?Cells $cellCollection;
 
     /**
      * Collection of row dimensions.
@@ -88,10 +84,8 @@ class Worksheet implements IComparable
 
     /**
      * Default row dimension.
-     *
-     * @var RowDimension
      */
-    private $defaultRowDimension;
+    private RowDimension $defaultRowDimension;
 
     /**
      * Collection of column dimensions.
@@ -102,31 +96,29 @@ class Worksheet implements IComparable
 
     /**
      * Default column dimension.
-     *
-     * @var ColumnDimension
      */
-    private $defaultColumnDimension;
+    private ColumnDimension $defaultColumnDimension;
 
     /**
      * Collection of drawings.
      *
      * @var ArrayObject<int, BaseDrawing>
      */
-    private $drawingCollection;
+    private ArrayObject $drawingCollection;
 
     /**
      * Collection of Chart objects.
      *
      * @var ArrayObject<int, Chart>
      */
-    private $chartCollection;
+    private ArrayObject $chartCollection;
 
     /**
      * Collection of Table objects.
      *
      * @var ArrayObject<int, Table>
      */
-    private $tableCollection;
+    private ArrayObject $tableCollection;
 
     /**
      * Worksheet title.
@@ -144,38 +136,28 @@ class Worksheet implements IComparable
 
     /**
      * Page setup.
-     *
-     * @var PageSetup
      */
-    private $pageSetup;
+    private PageSetup $pageSetup;
 
     /**
      * Page margins.
-     *
-     * @var PageMargins
      */
-    private $pageMargins;
+    private PageMargins $pageMargins;
 
     /**
      * Page header/footer.
-     *
-     * @var HeaderFooter
      */
-    private $headerFooter;
+    private HeaderFooter $headerFooter;
 
     /**
      * Sheet view.
-     *
-     * @var SheetView
      */
-    private $sheetView;
+    private SheetView $sheetView;
 
     /**
      * Protection.
-     *
-     * @var Protection
      */
-    private $protection;
+    private Protection $protection;
 
     /**
      * Collection of styles.
@@ -221,10 +203,8 @@ class Worksheet implements IComparable
 
     /**
      * Autofilter Range and selection.
-     *
-     * @var AutoFilter
      */
-    private $autoFilter;
+    private AutoFilter $autoFilter;
 
     /**
      * Freeze pane.
@@ -428,7 +408,6 @@ public function disconnectCells(): void
     {
         if ($this->cellCollection !== null) {
             $this->cellCollection->unsetWorksheetCells();
-            // @phpstan-ignore-next-line
             $this->cellCollection = null;
         }
         //    detach ourself from the workbook, so that it can then delete this worksheet successfully
@@ -454,6 +433,7 @@ public function __destruct()
      */
     public function getCellCollection()
     {
+        // @phpstan-ignore-next-line
         return $this->cellCollection;
     }
 
@@ -474,7 +454,7 @@ public static function getInvalidCharacters()
      *
      * @return string The valid string
      */
-    private static function checkSheetCodeName($sheetCodeName)
+    private static function checkSheetCodeName($sheetCodeName): string
     {
         $charCount = Shared\StringHelper::countCharacters($sheetCodeName);
         if ($charCount == 0) {
@@ -504,7 +484,7 @@ private static function checkSheetCodeName($sheetCodeName)
      *
      * @return string The valid string
      */
-    private static function checkSheetTitle($sheetTitle)
+    private static function checkSheetTitle($sheetTitle): string
     {
         // Some of the printable ASCII characters are invalid:  * : / \ ? [ ]
         if (str_replace(self::$invalidCharacters, '', $sheetTitle) !== $sheetTitle) {
@@ -526,7 +506,7 @@ private static function checkSheetTitle($sheetTitle)
      *
      * @return string[]
      */
-    public function getCoordinates($sorted = true)
+    public function getCoordinates($sorted = true): array
     {
         if ($this->cellCollection == null) {
             return [];
@@ -612,10 +592,8 @@ public function getChartCollection()
      * Add chart.
      *
      * @param null|int $chartIndex Index where chart should go (0,1,..., or null for last)
-     *
-     * @return Chart
      */
-    public function addChart(Chart $chart, $chartIndex = null)
+    public function addChart(Chart $chart, $chartIndex = null): Chart
     {
         $chart->setWorksheet($this);
         if ($chartIndex === null) {
@@ -634,7 +612,7 @@ public function addChart(Chart $chart, $chartIndex = null)
      *
      * @return int The number of charts
      */
-    public function getChartCount()
+    public function getChartCount(): int
     {
         return count($this->chartCollection);
     }
@@ -667,7 +645,7 @@ public function getChartByIndex($index)
      *
      * @return string[] The names of charts
      */
-    public function getChartNames()
+    public function getChartNames(): array
     {
         $chartNames = [];
         foreach ($this->chartCollection as $chart) {
@@ -700,7 +678,7 @@ public function getChartByName($chartName)
      *
      * @return $this
      */
-    public function refreshColumnDimensions()
+    public function refreshColumnDimensions(): static
     {
         $newColumnDimensions = [];
         foreach ($this->getColumnDimensions() as $objColumnDimension) {
@@ -717,7 +695,7 @@ public function refreshColumnDimensions()
      *
      * @return $this
      */
-    public function refreshRowDimensions()
+    public function refreshRowDimensions(): static
     {
         $newRowDimensions = [];
         foreach ($this->getRowDimensions() as $objRowDimension) {
@@ -734,7 +712,7 @@ public function refreshRowDimensions()
      *
      * @return string String containing the dimension of this worksheet
      */
-    public function calculateWorksheetDimension()
+    public function calculateWorksheetDimension(): string
     {
         // Return
         return 'A1:' . $this->getHighestColumn() . $this->getHighestRow();
@@ -745,7 +723,7 @@ public function calculateWorksheetDimension()
      *
      * @return string String containing the dimension of this worksheet that actually contain data
      */
-    public function calculateWorksheetDataDimension()
+    public function calculateWorksheetDataDimension(): string
     {
         // Return
         return 'A1:' . $this->getHighestDataColumn() . $this->getHighestDataRow();
@@ -756,7 +734,7 @@ public function calculateWorksheetDataDimension()
      *
      * @return $this
      */
-    public function calculateColumnWidths()
+    public function calculateColumnWidths(): static
     {
         // initialize $autoSizes array
         $autoSizes = [];
@@ -782,9 +760,9 @@ public function calculateColumnWidths()
             foreach ($this->getCoordinates(false) as $coordinate) {
                 $cell = $this->getCellOrNull($coordinate);
 
-                if ($cell !== null && isset($autoSizes[$this->cellCollection->getCurrentColumn()])) {
+                if ($cell !== null && isset($autoSizes[$this->getCellCollection()->getCurrentColumn()])) {
                     //Determine if cell is in merge range
-                    $isMerged = isset($isMergeCell[$this->cellCollection->getCurrentCoordinate()]);
+                    $isMerged = isset($isMergeCell[$this->getCellCollection()->getCurrentCoordinate()]);
 
                     //By default merged cells should be ignored
                     $isMergedButProceed = false;
@@ -825,8 +803,8 @@ public function calculateColumnWidths()
                         );
 
                         if ($cellValue !== null && $cellValue !== '') {
-                            $autoSizes[$this->cellCollection->getCurrentColumn()] = max(
-                                $autoSizes[$this->cellCollection->getCurrentColumn()],
+                            $autoSizes[$this->getCellCollection()->getCurrentColumn()] = max(
+                                $autoSizes[$this->getCellCollection()->getCurrentColumn()],
                                 round(
                                     Shared\Font::calculateColumnWidth(
                                         $this->getParentOrThrow()->getCellXfByIndex($cell->getXfIndex())->getFont(),
@@ -882,7 +860,7 @@ public function getParentOrThrow(): Spreadsheet
      *
      * @return $this
      */
-    public function rebindParent(Spreadsheet $parent)
+    public function rebindParent(Spreadsheet $parent): static
     {
         if ($this->parent !== null) {
             $definedNames = $this->parent->getDefinedNames();
@@ -923,7 +901,7 @@ public function getTitle()
      *
      * @return $this
      */
-    public function setTitle($title, $updateFormulaCellReferences = true, $validate = true)
+    public function setTitle($title, $updateFormulaCellReferences = true, $validate = true): static
     {
         // Is this a 'rename' or not?
         if ($this->getTitle() == $title) {
@@ -998,7 +976,7 @@ public function getSheetState()
      *
      * @return $this
      */
-    public function setSheetState($value)
+    public function setSheetState($value): static
     {
         $this->sheetState = $value;
 
@@ -1020,7 +998,7 @@ public function getPageSetup()
      *
      * @return $this
      */
-    public function setPageSetup(PageSetup $pageSetup)
+    public function setPageSetup(PageSetup $pageSetup): static
     {
         $this->pageSetup = $pageSetup;
 
@@ -1042,7 +1020,7 @@ public function getPageMargins()
      *
      * @return $this
      */
-    public function setPageMargins(PageMargins $pageMargins)
+    public function setPageMargins(PageMargins $pageMargins): static
     {
         $this->pageMargins = $pageMargins;
 
@@ -1064,7 +1042,7 @@ public function getHeaderFooter()
      *
      * @return $this
      */
-    public function setHeaderFooter(HeaderFooter $headerFooter)
+    public function setHeaderFooter(HeaderFooter $headerFooter): static
     {
         $this->headerFooter = $headerFooter;
 
@@ -1086,7 +1064,7 @@ public function getSheetView()
      *
      * @return $this
      */
-    public function setSheetView(SheetView $sheetView)
+    public function setSheetView(SheetView $sheetView): static
     {
         $this->sheetView = $sheetView;
 
@@ -1108,7 +1086,7 @@ public function getProtection()
      *
      * @return $this
      */
-    public function setProtection(Protection $protection)
+    public function setProtection(Protection $protection): static
     {
         $this->protection = $protection;
         $this->dirty = true;
@@ -1143,7 +1121,7 @@ public function getHighestColumn($row = null)
      */
     public function getHighestDataColumn($row = null)
     {
-        return $this->cellCollection->getHighestColumn($row);
+        return $this->getCellCollection()->getHighestColumn($row);
     }
 
     /**
@@ -1173,7 +1151,7 @@ public function getHighestRow($column = null)
      */
     public function getHighestDataRow($column = null)
     {
-        return $this->cellCollection->getHighestRow($column);
+        return $this->getCellCollection()->getHighestRow($column);
     }
 
     /**
@@ -1181,9 +1159,9 @@ public function getHighestDataRow($column = null)
      *
      * @return array Highest column name and highest row number
      */
-    public function getHighestRowAndColumn()
+    public function getHighestRowAndColumn(): array
     {
-        return $this->cellCollection->getHighestRowAndColumn();
+        return $this->getCellCollection()->getHighestRowAndColumn();
     }
 
     /**
@@ -1196,7 +1174,7 @@ public function getHighestRowAndColumn()
      *
      * @return $this
      */
-    public function setCellValue($coordinate, $value, ?IValueBinder $binder = null)
+    public function setCellValue($coordinate, $value, ?IValueBinder $binder = null): static
     {
         $cellAddress = Functions::trimSheetFromCellReference(Validations::validateCellAddress($coordinate));
         $this->getCell($cellAddress)->setValue($value, $binder);
@@ -1219,7 +1197,7 @@ public function setCellValue($coordinate, $value, ?IValueBinder $binder = null)
      *
      * @return $this
      */
-    public function setCellValueByColumnAndRow($columnIndex, $row, $value, ?IValueBinder $binder = null)
+    public function setCellValueByColumnAndRow($columnIndex, $row, $value, ?IValueBinder $binder = null): static
     {
         $this->getCell(Coordinate::stringFromColumnIndex($columnIndex) . $row)->setValue($value, $binder);
 
@@ -1243,7 +1221,7 @@ public function setCellValueByColumnAndRow($columnIndex, $row, $value, ?IValueBi
      *
      * @return $this
      */
-    public function setCellValueExplicit($coordinate, $value, $dataType)
+    public function setCellValueExplicit($coordinate, $value, string $dataType): static
     {
         $cellAddress = Functions::trimSheetFromCellReference(Validations::validateCellAddress($coordinate));
         $this->getCell($cellAddress)->setValueExplicit($value, $dataType);
@@ -1273,7 +1251,7 @@ public function setCellValueExplicit($coordinate, $value, $dataType)
      *
      * @return $this
      */
-    public function setCellValueExplicitByColumnAndRow($columnIndex, $row, $value, $dataType)
+    public function setCellValueExplicitByColumnAndRow($columnIndex, $row, $value, string $dataType): static
     {
         $this->getCell(Coordinate::stringFromColumnIndex($columnIndex) . $row)->setValueExplicit($value, $dataType);
 
@@ -1298,16 +1276,16 @@ public function getCell($coordinate): Cell
         $cellAddress = Functions::trimSheetFromCellReference(Validations::validateCellAddress($coordinate));
 
         // Shortcut for increased performance for the vast majority of simple cases
-        if ($this->cellCollection->has($cellAddress)) {
+        if ($this->getCellCollection()->has($cellAddress)) {
             /** @var Cell $cell */
-            $cell = $this->cellCollection->get($cellAddress);
+            $cell = $this->getCellCollection()->get($cellAddress);
 
             return $cell;
         }
 
         /** @var Worksheet $sheet */
         [$sheet, $finalCoordinate] = $this->getWorksheetAndCoordinate($cellAddress);
-        $cell = $sheet->cellCollection->get($finalCoordinate);
+        $cell = $sheet->getCellCollection()->get($finalCoordinate);
 
         return $cell ?? $sheet->createNewCell($finalCoordinate);
     }
@@ -1375,8 +1353,8 @@ private function getWorksheetAndCoordinate(string $coordinate): array
     private function getCellOrNull($coordinate): ?Cell
     {
         // Check cell collection
-        if ($this->cellCollection->has($coordinate)) {
-            return $this->cellCollection->get($coordinate);
+        if ($this->getCellCollection()->has($coordinate)) {
+            return $this->getCellCollection()->get($coordinate);
         }
 
         return null;
@@ -1417,11 +1395,11 @@ public function getCellByColumnAndRow($columnIndex, $row): Cell
      *              the "active" cell, and any previous assignment becomes a disconnected reference because
      *              the active cell has changed.
      */
-    public function createNewCell($coordinate): Cell
+    public function createNewCell(string $coordinate): Cell
     {
         [$column, $row, $columnString] = Coordinate::indexesFromString($coordinate);
         $cell = new Cell(null, DataType::TYPE_NULL, $this);
-        $this->cellCollection->add($coordinate, $cell);
+        $this->getCellCollection()->add($coordinate, $cell);
 
         // Coordinates
         if ($column > $this->cachedHighestColumn) {
@@ -1465,10 +1443,9 @@ public function createNewCell($coordinate): Cell
     public function cellExists($coordinate): bool
     {
         $cellAddress = Validations::validateCellAddress($coordinate);
-        /** @var Worksheet $sheet */
         [$sheet, $finalCoordinate] = $this->getWorksheetAndCoordinate($cellAddress);
 
-        return $sheet->cellCollection->has($finalCoordinate);
+        return $sheet->getCellCollection()->has($finalCoordinate);
     }
 
     /**
@@ -1586,10 +1563,8 @@ public function getStyle($cellCoordinate): Style
      * @param int $row1 Numeric row coordinate of the cell
      * @param null|int $columnIndex2 Numeric column coordinate of the range cell
      * @param null|int $row2 Numeric row coordinate of the range cell
-     *
-     * @return Style
      */
-    public function getStyleByColumnAndRow($columnIndex1, $row1, $columnIndex2 = null, $row2 = null)
+    public function getStyleByColumnAndRow($columnIndex1, $row1, $columnIndex2 = null, $row2 = null): Style
     {
         if ($columnIndex2 !== null && $row2 !== null) {
             $cellRange = new CellRange(
@@ -1677,7 +1652,7 @@ public function conditionalStylesExists($coordinate): bool
      *
      * @return $this
      */
-    public function removeConditionalStyles($coordinate)
+    public function removeConditionalStyles($coordinate): static
     {
         unset($this->conditionalStylesCollection[strtoupper($coordinate)]);
 
@@ -1702,7 +1677,7 @@ public function getConditionalStylesCollection()
      *
      * @return $this
      */
-    public function setConditionalStyles($coordinate, $styles)
+    public function setConditionalStyles($coordinate, $styles): static
     {
         $this->conditionalStylesCollection[strtoupper($coordinate)] = $styles;
 
@@ -1719,7 +1694,7 @@ public function setConditionalStyles($coordinate, $styles)
      *
      * @return $this
      */
-    public function duplicateStyle(Style $style, $range)
+    public function duplicateStyle(Style $style, string $range): static
     {
         // Add the style to the workbook if necessary
         $workbook = $this->getParentOrThrow();
@@ -1762,7 +1737,7 @@ public function duplicateStyle(Style $style, $range)
      *
      * @return $this
      */
-    public function duplicateConditionalStyle(array $styles, $range = '')
+    public function duplicateConditionalStyle(array $styles, string $range = ''): static
     {
         foreach ($styles as $cellStyle) {
             if (!($cellStyle instanceof Conditional)) {
@@ -1799,7 +1774,7 @@ public function duplicateConditionalStyle(array $styles, $range = '')
      *
      * @return $this
      */
-    public function setBreak($coordinate, $break, int $max = -1)
+    public function setBreak($coordinate, $break, int $max = -1): static
     {
         $cellAddress = Functions::trimSheetFromCellReference(Validations::validateCellAddress($coordinate));
 
@@ -1828,7 +1803,7 @@ public function setBreak($coordinate, $break, int $max = -1)
      *
      * @return $this
      */
-    public function setBreakByColumnAndRow($columnIndex, $row, $break)
+    public function setBreakByColumnAndRow($columnIndex, $row, $break): static
     {
         return $this->setBreak(Coordinate::stringFromColumnIndex($columnIndex) . $row, $break);
     }
@@ -1838,7 +1813,7 @@ public function setBreakByColumnAndRow($columnIndex, $row, $break)
      *
      * @return int[]
      */
-    public function getBreaks()
+    public function getBreaks(): array
     {
         $breaks = [];
         /** @var callable */
@@ -1915,7 +1890,7 @@ public function getColumnBreaks()
      *
      * @return $this
      */
-    public function mergeCells($range, $behaviour = self::MERGE_CELL_CONTENT_EMPTY)
+    public function mergeCells($range, $behaviour = self::MERGE_CELL_CONTENT_EMPTY): static
     {
         $range = Functions::trimSheetFromCellReference(Validations::validateCellRange($range));
 
@@ -2047,7 +2022,7 @@ public function mergeCellBehaviour(Cell $cell, string $upperLeft, string $behavi
      *
      * @return $this
      */
-    public function mergeCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2, $behaviour = self::MERGE_CELL_CONTENT_EMPTY)
+    public function mergeCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2, $behaviour = self::MERGE_CELL_CONTENT_EMPTY): static
     {
         $cellRange = new CellRange(
             CellAddress::fromColumnAndRow($columnIndex1, $row1),
@@ -2066,7 +2041,7 @@ public function mergeCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $r
      *
      * @return $this
      */
-    public function unmergeCells($range)
+    public function unmergeCells($range): static
     {
         $range = Functions::trimSheetFromCellReference(Validations::validateCellRange($range));
 
@@ -2099,7 +2074,7 @@ public function unmergeCells($range)
      *
      * @return $this
      */
-    public function unmergeCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2)
+    public function unmergeCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2): static
     {
         $cellRange = new CellRange(
             CellAddress::fromColumnAndRow($columnIndex1, $row1),
@@ -2127,7 +2102,7 @@ public function getMergeCells()
      *
      * @return $this
      */
-    public function setMergeCells(array $mergeCells)
+    public function setMergeCells(array $mergeCells): static
     {
         $this->mergeCells = $mergeCells;
 
@@ -2145,7 +2120,7 @@ public function setMergeCells(array $mergeCells)
      *
      * @return $this
      */
-    public function protectCells($range, $password, $alreadyHashed = false)
+    public function protectCells($range, $password, $alreadyHashed = false): static
     {
         $range = Functions::trimSheetFromCellReference(Validations::validateCellOrCellRange($range));
 
@@ -2175,7 +2150,7 @@ public function protectCells($range, $password, $alreadyHashed = false)
      *
      * @return $this
      */
-    public function protectCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2, $password, $alreadyHashed = false)
+    public function protectCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2, $password, $alreadyHashed = false): static
     {
         $cellRange = new CellRange(
             CellAddress::fromColumnAndRow($columnIndex1, $row1),
@@ -2194,7 +2169,7 @@ public function protectCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2,
      *
      * @return $this
      */
-    public function unprotectCells($range)
+    public function unprotectCells($range): static
     {
         $range = Functions::trimSheetFromCellReference(Validations::validateCellOrCellRange($range));
 
@@ -2223,7 +2198,7 @@ public function unprotectCells($range)
      *
      * @return $this
      */
-    public function unprotectCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2)
+    public function unprotectCellsByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2): static
     {
         $cellRange = new CellRange(
             CellAddress::fromColumnAndRow($columnIndex1, $row1),
@@ -2263,7 +2238,7 @@ public function getAutoFilter()
      *
      * @return $this
      */
-    public function setAutoFilter($autoFilterOrRange)
+    public function setAutoFilter($autoFilterOrRange): static
     {
         if (is_object($autoFilterOrRange) && ($autoFilterOrRange instanceof AutoFilter)) {
             $this->autoFilter = $autoFilterOrRange;
@@ -2292,7 +2267,7 @@ public function setAutoFilter($autoFilterOrRange)
      *
      * @return $this
      */
-    public function setAutoFilterByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2)
+    public function setAutoFilterByColumnAndRow($columnIndex1, $row1, $columnIndex2, $row2): static
     {
         $cellRange = new CellRange(
             CellAddress::fromColumnAndRow($columnIndex1, $row1),
@@ -2442,7 +2417,7 @@ public function getFreezePane()
      *
      * @return $this
      */
-    public function freezePane($coordinate, $topLeftCell = null, bool $frozenSplit = false)
+    public function freezePane($coordinate, $topLeftCell = null, bool $frozenSplit = false): static
     {
         $this->panes = [
             'bottomRight' => null,
@@ -2511,7 +2486,7 @@ public function setTopLeftCell(string $topLeftCell): self
      *
      * @return $this
      */
-    public function freezePaneByColumnAndRow($columnIndex, $row)
+    public function freezePaneByColumnAndRow($columnIndex, $row): static
     {
         return $this->freezePane(Coordinate::stringFromColumnIndex($columnIndex) . $row);
     }
@@ -2521,7 +2496,7 @@ public function freezePaneByColumnAndRow($columnIndex, $row)
      *
      * @return $this
      */
-    public function unfreezePane()
+    public function unfreezePane(): static
     {
         return $this->freezePane(null);
     }
@@ -2646,7 +2621,7 @@ public function setPaneState(string $paneState): self
      *
      * @return $this
      */
-    public function insertNewRowBefore(int $before, int $numberOfRows = 1)
+    public function insertNewRowBefore(int $before, int $numberOfRows = 1): static
     {
         if ($before >= 1) {
             $objReferenceHelper = ReferenceHelper::getInstance();
@@ -2666,7 +2641,7 @@ public function insertNewRowBefore(int $before, int $numberOfRows = 1)
      *
      * @return $this
      */
-    public function insertNewColumnBefore(string $before, int $numberOfColumns = 1)
+    public function insertNewColumnBefore(string $before, int $numberOfColumns = 1): static
     {
         if (!is_numeric($before)) {
             $objReferenceHelper = ReferenceHelper::getInstance();
@@ -2686,7 +2661,7 @@ public function insertNewColumnBefore(string $before, int $numberOfColumns = 1)
      *
      * @return $this
      */
-    public function insertNewColumnBeforeByIndex(int $beforeColumnIndex, int $numberOfColumns = 1)
+    public function insertNewColumnBeforeByIndex(int $beforeColumnIndex, int $numberOfColumns = 1): static
     {
         if ($beforeColumnIndex >= 1) {
             return $this->insertNewColumnBefore(Coordinate::stringFromColumnIndex($beforeColumnIndex), $numberOfColumns);
@@ -2703,7 +2678,7 @@ public function insertNewColumnBeforeByIndex(int $beforeColumnIndex, int $number
      *
      * @return $this
      */
-    public function removeRow(int $row, int $numberOfRows = 1)
+    public function removeRow(int $row, int $numberOfRows = 1): static
     {
         if ($row < 1) {
             throw new Exception('Rows to be deleted should at least start from row 1.');
@@ -2759,7 +2734,7 @@ private function removeRowDimensions(int $row, int $numberOfRows): array
      *
      * @return $this
      */
-    public function removeColumn(string $column, int $numberOfColumns = 1)
+    public function removeColumn(string $column, int $numberOfColumns = 1): static
     {
         if (is_numeric($column)) {
             throw new Exception('Column references should not be numeric.');
@@ -2821,7 +2796,7 @@ private function removeColumnDimensions(int $pColumnIndex, int $numberOfColumns)
      *
      * @return $this
      */
-    public function removeColumnByIndex(int $columnIndex, int $numColumns = 1)
+    public function removeColumnByIndex(int $columnIndex, int $numColumns = 1): static
     {
         if ($columnIndex >= 1) {
             return $this->removeColumn(Coordinate::stringFromColumnIndex($columnIndex), $numColumns);
@@ -3064,7 +3039,7 @@ public function getSelectedCells()
      *
      * @return $this
      */
-    public function setSelectedCell($coordinate)
+    public function setSelectedCell($coordinate): static
     {
         return $this->setSelectedCells($coordinate);
     }
@@ -3078,7 +3053,7 @@ public function setSelectedCell($coordinate)
      *
      * @return $this
      */
-    public function setSelectedCells($coordinate)
+    public function setSelectedCells($coordinate): static
     {
         if (is_string($coordinate)) {
             $coordinate = Validations::definedNameToCoordinate($coordinate, $this);
@@ -3129,7 +3104,7 @@ private function setSelectedCellsActivePane(): void
      *
      * @return $this
      */
-    public function setSelectedCellByColumnAndRow($columnIndex, $row)
+    public function setSelectedCellByColumnAndRow($columnIndex, $row): static
     {
         return $this->setSelectedCells(Coordinate::stringFromColumnIndex($columnIndex) . $row);
     }
@@ -3151,7 +3126,7 @@ public function getRightToLeft()
      *
      * @return $this
      */
-    public function setRightToLeft($value)
+    public function setRightToLeft($value): static
     {
         $this->rightToLeft = $value;
 
@@ -3168,7 +3143,7 @@ public function setRightToLeft($value)
      *
      * @return $this
      */
-    public function fromArray(array $source, $nullValue = null, $startCell = 'A1', $strictNullComparison = false)
+    public function fromArray(array $source, $nullValue = null, $startCell = 'A1', $strictNullComparison = false): static
     {
         //    Convert a 1-D array to 2-D (for ease of looping)
         if (!is_array(end($source))) {
@@ -3278,7 +3253,7 @@ public function rangeToArray(
                 $columnRef = $returnCellRef ? $col : ++$c;
                 //    Using getCell() will create a new cell if it doesn't already exist. We don't want that to happen
                 //        so we test and retrieve directly against cellCollection
-                $cell = $this->cellCollection->get("{$col}{$row}");
+                $cell = $this->getCellCollection()->get("{$col}{$row}");
                 $returnValue[$rowRef][$columnRef] = $nullValue;
                 if ($cell !== null) {
                     $returnValue[$rowRef][$columnRef] = $this->cellToArray($cell, $calculateFormulas, $formatData, $nullValue);
@@ -3393,10 +3368,8 @@ public function toArray(
      *
      * @param int $startRow The row number at which to start iterating
      * @param int $endRow The row number at which to stop iterating
-     *
-     * @return RowIterator
      */
-    public function getRowIterator($startRow = 1, $endRow = null)
+    public function getRowIterator($startRow = 1, $endRow = null): RowIterator
     {
         return new RowIterator($this, $startRow, $endRow);
     }
@@ -3406,10 +3379,8 @@ public function getRowIterator($startRow = 1, $endRow = null)
      *
      * @param string $startColumn The column address at which to start iterating
      * @param string $endColumn The column address at which to stop iterating
-     *
-     * @return ColumnIterator
      */
-    public function getColumnIterator($startColumn = 'A', $endColumn = null)
+    public function getColumnIterator($startColumn = 'A', $endColumn = null): ColumnIterator
     {
         return new ColumnIterator($this, $startColumn, $endColumn);
     }
@@ -3419,13 +3390,13 @@ public function getColumnIterator($startColumn = 'A', $endColumn = null)
      *
      * @return $this
      */
-    public function garbageCollect()
+    public function garbageCollect(): static
     {
         // Flush cache
-        $this->cellCollection->get('A1');
+        $this->getCellCollection()->get('A1');
 
         // Lookup highest column and highest row if cells are cleaned
-        $colRow = $this->cellCollection->getHighestRowAndColumn();
+        $colRow = $this->getCellCollection()->getHighestRowAndColumn();
         $highestRow = $colRow['row'];
         $highestColumn = Coordinate::columnIndexFromString($colRow['column']);
 
@@ -3479,9 +3450,9 @@ public function getHashCode()
      * @param string $range Range to extract title from
      * @param bool $returnRange Return range? (see example)
      *
-     * @return mixed
+     * @return ($range is non-empty-string ? ($returnRange is true ? array{0: string, 1: string} : string) : ($returnRange is true ? array{0: null, 1: null} : null))
      */
-    public static function extractSheetTitle($range, $returnRange = false)
+    public static function extractSheetTitle($range, $returnRange = false): array|null|string
     {
         if (empty($range)) {
             return $returnRange ? [null, null] : null;
@@ -3526,7 +3497,7 @@ public function getHyperlink($cellCoordinate)
      *
      * @return $this
      */
-    public function setHyperlink($cellCoordinate, ?Hyperlink $hyperlink = null)
+    public function setHyperlink($cellCoordinate, ?Hyperlink $hyperlink = null): static
     {
         if ($hyperlink === null) {
             unset($this->hyperlinkCollection[$cellCoordinate]);
@@ -3541,10 +3512,8 @@ public function setHyperlink($cellCoordinate, ?Hyperlink $hyperlink = null)
      * Hyperlink at a specific coordinate exists?
      *
      * @param string $coordinate eg: 'A1'
-     *
-     * @return bool
      */
-    public function hyperlinkExists($coordinate)
+    public function hyperlinkExists($coordinate): bool
     {
         return isset($this->hyperlinkCollection[$coordinate]);
     }
@@ -3586,7 +3555,7 @@ public function getDataValidation($cellCoordinate)
      *
      * @return $this
      */
-    public function setDataValidation($cellCoordinate, ?DataValidation $dataValidation = null)
+    public function setDataValidation($cellCoordinate, ?DataValidation $dataValidation = null): static
     {
         if ($dataValidation === null) {
             unset($this->dataValidationCollection[$cellCoordinate]);
@@ -3601,10 +3570,8 @@ public function setDataValidation($cellCoordinate, ?DataValidation $dataValidati
      * Data validation at a specific coordinate exists?
      *
      * @param string $coordinate eg: 'A1'
-     *
-     * @return bool
      */
-    public function dataValidationExists($coordinate)
+    public function dataValidationExists($coordinate): bool
     {
         return isset($this->dataValidationCollection[$coordinate]);
     }
@@ -3626,7 +3593,7 @@ public function getDataValidationCollection()
      *
      * @return string Adjusted range value
      */
-    public function shrinkRangeToFit($range)
+    public function shrinkRangeToFit($range): string
     {
         $maxCol = $this->getHighestColumn();
         $maxRow = $this->getHighestRow();
@@ -3674,7 +3641,7 @@ public function getTabColor()
      *
      * @return $this
      */
-    public function resetTabColor()
+    public function resetTabColor(): static
     {
         $this->tabColor = null;
 
@@ -3683,20 +3650,16 @@ public function resetTabColor()
 
     /**
      * Tab color set?
-     *
-     * @return bool
      */
-    public function isTabColorSet()
+    public function isTabColorSet(): bool
     {
         return $this->tabColor !== null;
     }
 
     /**
      * Copy worksheet (!= clone!).
-     *
-     * @return static
      */
-    public function copy()
+    public function copy(): static
     {
         return clone $this;
     }
@@ -3774,7 +3737,7 @@ public function __clone()
 
             if (is_object($val) || (is_array($val))) {
                 if ($key == 'cellCollection') {
-                    $newCollection = $this->cellCollection->cloneCellCollection($this);
+                    $newCollection = $this->getCellCollection()->cloneCellCollection($this);
                     $this->cellCollection = $newCollection;
                 } elseif ($key == 'drawingCollection') {
                     $currentCollection = $this->drawingCollection;
@@ -3806,7 +3769,7 @@ public function __clone()
      *
      * @return $this
      */
-    public function setCodeName($codeName, $validate = true)
+    public function setCodeName($codeName, $validate = true): static
     {
         // Is this a 'rename' or not?
         if ($this->getCodeName() == $codeName) {
@@ -3866,10 +3829,8 @@ public function getCodeName()
 
     /**
      * Sheet has a code name ?
-     *
-     * @return bool
      */
-    public function hasCodeName()
+    public function hasCodeName(): bool
     {
         return $this->codeName !== null;
     }
diff --git a/src/PhpSpreadsheet/Writer/Csv.php b/src/PhpSpreadsheet/Writer/Csv.php
index 8f0ceda358..1099ffbc56 100644
--- a/src/PhpSpreadsheet/Writer/Csv.php
+++ b/src/PhpSpreadsheet/Writer/Csv.php
@@ -9,24 +9,18 @@ class Csv extends BaseWriter
 {
     /**
      * PhpSpreadsheet object.
-     *
-     * @var Spreadsheet
      */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     /**
      * Delimiter.
-     *
-     * @var string
      */
-    private $delimiter = ',';
+    private string $delimiter = ',';
 
     /**
      * Enclosure.
-     *
-     * @var string
      */
-    private $enclosure = '"';
+    private string $enclosure = '"';
 
     /**
      * Line ending.
@@ -66,10 +60,8 @@ class Csv extends BaseWriter
 
     /**
      * Output encoding.
-     *
-     * @var string
      */
-    private $outputEncoding = '';
+    private string $outputEncoding = '';
 
     /**
      * Create a new CSV.
diff --git a/src/PhpSpreadsheet/Writer/Html.php b/src/PhpSpreadsheet/Writer/Html.php
index 9e1df0dc16..22af8bcdf8 100644
--- a/src/PhpSpreadsheet/Writer/Html.php
+++ b/src/PhpSpreadsheet/Writer/Html.php
@@ -33,10 +33,8 @@ class Html extends BaseWriter
 {
     /**
      * Spreadsheet object.
-     *
-     * @var Spreadsheet
      */
-    protected $spreadsheet;
+    protected Spreadsheet $spreadsheet;
 
     /**
      * Sheet index to write.
@@ -89,10 +87,8 @@ class Html extends BaseWriter
 
     /**
      * Default font.
-     *
-     * @var Font
      */
-    private $defaultFont;
+    private Font $defaultFont;
 
     /**
      * Flag whether spans have been calculated.
@@ -237,10 +233,8 @@ public function setEditHtmlCallback(?callable $callback): void
      * Map VAlign.
      *
      * @param string $vAlign Vertical alignment
-     *
-     * @return string
      */
-    private function mapVAlign($vAlign)
+    private function mapVAlign($vAlign): string
     {
         return Alignment::VERTICAL_ALIGNMENT_FOR_HTML[$vAlign] ?? '';
     }
@@ -249,10 +243,8 @@ private function mapVAlign($vAlign)
      * Map HAlign.
      *
      * @param string $hAlign Horizontal alignment
-     *
-     * @return string
      */
-    private function mapHAlign($hAlign)
+    private function mapHAlign($hAlign): string
     {
         return Alignment::HORIZONTAL_ALIGNMENT_FOR_HTML[$hAlign] ?? '';
     }
@@ -276,10 +268,8 @@ private function mapHAlign($hAlign)
      * Map border style.
      *
      * @param int|string $borderStyle Sheet index
-     *
-     * @return string
      */
-    private function mapBorderStyle($borderStyle)
+    private function mapBorderStyle($borderStyle): string
     {
         return array_key_exists($borderStyle, self::BORDER_ARR) ? self::BORDER_ARR[$borderStyle] : '1px solid';
     }
@@ -299,7 +289,7 @@ public function getSheetIndex(): ?int
      *
      * @return $this
      */
-    public function setSheetIndex($sheetIndex)
+    public function setSheetIndex($sheetIndex): static
     {
         $this->sheetIndex = $sheetIndex;
 
@@ -323,7 +313,7 @@ public function getGenerateSheetNavigationBlock()
      *
      * @return $this
      */
-    public function setGenerateSheetNavigationBlock($generateSheetNavigationBlock)
+    public function setGenerateSheetNavigationBlock($generateSheetNavigationBlock): static
     {
         $this->generateSheetNavigationBlock = (bool) $generateSheetNavigationBlock;
 
@@ -335,7 +325,7 @@ public function setGenerateSheetNavigationBlock($generateSheetNavigationBlock)
      *
      * @return $this
      */
-    public function writeAllSheets()
+    public function writeAllSheets(): static
     {
         $this->sheetIndex = null;
 
@@ -363,10 +353,8 @@ private static function generateMeta(?string $val, string $desc): string
      * Generate HTML header.
      *
      * @param bool $includeStyles Include styles?
-     *
-     * @return string
      */
-    public function generateHTMLHeader($includeStyles = false)
+    public function generateHTMLHeader($includeStyles = false): string
     {
         // Construct HTML
         $properties = $this->spreadsheet->getProperties();
@@ -474,10 +462,8 @@ private function generateSheetTags(int $row, int $theadStart, int $theadEnd, int
 
     /**
      * Generate sheet data.
-     *
-     * @return string
      */
-    public function generateSheetData()
+    public function generateSheetData(): string
     {
         $sheets = $this->generateSheetPrep();
 
@@ -541,10 +527,8 @@ public function generateSheetData()
 
     /**
      * Generate sheet tabs.
-     *
-     * @return string
      */
-    public function generateNavigation()
+    public function generateNavigation(): string
     {
         // Fetch sheets
         $sheets = [];
@@ -581,10 +565,8 @@ public function generateNavigation()
      * Chart/32_Chart_read_write_PDF.php.
      *
      * @param int $row Row to check for charts
-     *
-     * @return array
      */
-    private function extendRowsForCharts(Worksheet $worksheet, int $row)
+    private function extendRowsForCharts(Worksheet $worksheet, int $row): array
     {
         $rowMax = $row;
         $colMax = 'A';
@@ -674,10 +656,8 @@ public static function winFileToUrl($filename, bool $mpdf = false)
      *
      * @param Worksheet $worksheet \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet
      * @param string $coordinates Cell coordinates
-     *
-     * @return string
      */
-    private function writeImageInCell(Worksheet $worksheet, $coordinates)
+    private function writeImageInCell(Worksheet $worksheet, string $coordinates): string
     {
         // Construct HTML
         $html = '';
@@ -794,10 +774,8 @@ private function writeChartInCell(Worksheet $worksheet, string $coordinates): st
      * Generate CSS styles.
      *
      * @param bool $generateSurroundingHTML Generate surrounding HTML tags? (&lt;style&gt; and &lt;/style&gt;)
-     *
-     * @return string
      */
-    public function generateStyles($generateSurroundingHTML = true)
+    public function generateStyles($generateSurroundingHTML = true): string
     {
         // Build CSS
         $css = $this->buildCSS($generateSurroundingHTML);
@@ -1002,10 +980,8 @@ public function buildCSS($generateSurroundingHTML = true)
 
     /**
      * Create CSS style.
-     *
-     * @return array
      */
-    private function createCSSStyle(Style $style)
+    private function createCSSStyle(Style $style): array
     {
         // Create CSS
         return array_merge(
@@ -1018,10 +994,8 @@ private function createCSSStyle(Style $style)
 
     /**
      * Create CSS style.
-     *
-     * @return array
      */
-    private function createCSSStyleAlignment(Alignment $alignment)
+    private function createCSSStyleAlignment(Alignment $alignment): array
     {
         // Construct CSS
         $css = [];
@@ -1052,10 +1026,8 @@ private function createCSSStyleAlignment(Alignment $alignment)
 
     /**
      * Create CSS style.
-     *
-     * @return array
      */
-    private function createCSSStyleFont(Font $font)
+    private function createCSSStyleFont(Font $font): array
     {
         // Construct CSS
         $css = [];
@@ -1086,10 +1058,8 @@ private function createCSSStyleFont(Font $font)
      * Create CSS style.
      *
      * @param Borders $borders Borders
-     *
-     * @return array
      */
-    private function createCSSStyleBorders(Borders $borders)
+    private function createCSSStyleBorders(Borders $borders): array
     {
         // Construct CSS
         $css = [];
@@ -1190,7 +1160,7 @@ private function generateTableTag(Worksheet $worksheet, string $id, string &$htm
      *
      * @return string
      */
-    private function generateTableHeader(Worksheet $worksheet, $showid = true)
+    private function generateTableHeader(Worksheet $worksheet, bool $showid = true)
     {
         $sheetIndex = $worksheet->getParentOrThrow()->getIndex($worksheet);
 
@@ -1234,10 +1204,8 @@ private function generateTableFooter(): string
      *
      * @param int $sheetIndex Sheet index (0-based)
      * @param int $row row number
-     *
-     * @return string
      */
-    private function generateRowStart(Worksheet $worksheet, $sheetIndex, $row)
+    private function generateRowStart(Worksheet $worksheet, $sheetIndex, int $row): string
     {
         $html = '';
         if (count($worksheet->getBreaks()) > 0) {
@@ -1492,10 +1460,8 @@ private function generateRowWriteCell(string &$html, Worksheet $worksheet, strin
      * @param array $values Array containing cells in a row
      * @param int $row Row number (0-based)
      * @param string $cellType eg: 'td'
-     *
-     * @return string
      */
-    private function generateRow(Worksheet $worksheet, array $values, $row, $cellType)
+    private function generateRow(Worksheet $worksheet, array $values, int $row, string $cellType): string
     {
         // Sheet index
         $sheetIndex = $worksheet->getParentOrThrow()->getIndex($worksheet);
@@ -1552,10 +1518,8 @@ private function generateRow(Worksheet $worksheet, array $values, $row, $cellTyp
 
     /**
      * Takes array where of CSS properties / values and converts to CSS string.
-     *
-     * @return string
      */
-    private function assembleCSS(array $values = [])
+    private function assembleCSS(array $values = []): string
     {
         $pairs = [];
         foreach ($values as $property => $value) {
@@ -1583,7 +1547,7 @@ public function getImagesRoot()
      *
      * @return $this
      */
-    public function setImagesRoot($imagesRoot)
+    public function setImagesRoot($imagesRoot): static
     {
         $this->imagesRoot = $imagesRoot;
 
@@ -1607,7 +1571,7 @@ public function getEmbedImages()
      *
      * @return $this
      */
-    public function setEmbedImages($embedImages)
+    public function setEmbedImages($embedImages): static
     {
         $this->embedImages = $embedImages;
 
@@ -1631,7 +1595,7 @@ public function getUseInlineCss()
      *
      * @return $this
      */
-    public function setUseInlineCss($useInlineCss)
+    public function setUseInlineCss($useInlineCss): static
     {
         $this->useInlineCss = $useInlineCss;
 
@@ -1663,7 +1627,7 @@ public function getUseEmbeddedCSS()
      *
      * @deprecated no longer used
      */
-    public function setUseEmbeddedCSS($useEmbeddedCSS)
+    public function setUseEmbeddedCSS($useEmbeddedCSS): static
     {
         $this->useEmbeddedCSS = $useEmbeddedCSS;
 
@@ -1675,10 +1639,8 @@ public function setUseEmbeddedCSS($useEmbeddedCSS)
      *
      * @param string $value Plain formatted value without color
      * @param string $format Format code
-     *
-     * @return string
      */
-    public function formatColor($value, $format)
+    public function formatColor($value, $format): string
     {
         // Color information, e.g. [Red] is always at the beginning
         $color = null; // initialize
@@ -1803,12 +1765,8 @@ private function calculateSpansOmitRows(Worksheet $sheet, int $sheetIndex, array
      * Write a comment in the same format as LibreOffice.
      *
      * @see https://github.com/LibreOffice/core/blob/9fc9bf3240f8c62ad7859947ab8a033ac1fe93fa/sc/source/filter/html/htmlexp.cxx#L1073-L1092
-     *
-     * @param string $coordinate
-     *
-     * @return string
      */
-    private function writeComment(Worksheet $worksheet, $coordinate)
+    private function writeComment(Worksheet $worksheet, string $coordinate): string
     {
         $result = '';
         if (!$this->isPdf && isset($worksheet->getComments()[$coordinate])) {
@@ -1836,12 +1794,8 @@ public function getOrientation(): ?string
 
     /**
      * Generate @page declarations.
-     *
-     * @param bool $generateSurroundingHTML
-     *
-     * @return    string
      */
-    private function generatePageDeclarations($generateSurroundingHTML)
+    private function generatePageDeclarations(bool $generateSurroundingHTML): string
     {
         // Ensure that Spans have been calculated?
         $this->calculateSpans();
diff --git a/src/PhpSpreadsheet/Writer/Ods.php b/src/PhpSpreadsheet/Writer/Ods.php
index c9e0ba839f..37e02563e8 100644
--- a/src/PhpSpreadsheet/Writer/Ods.php
+++ b/src/PhpSpreadsheet/Writer/Ods.php
@@ -23,40 +23,19 @@ class Ods extends BaseWriter
      */
     private $spreadSheet;
 
-    /**
-     * @var Content
-     */
-    private $writerPartContent;
+    private Content $writerPartContent;
 
-    /**
-     * @var Meta
-     */
-    private $writerPartMeta;
+    private Meta $writerPartMeta;
 
-    /**
-     * @var MetaInf
-     */
-    private $writerPartMetaInf;
+    private MetaInf $writerPartMetaInf;
 
-    /**
-     * @var Mimetype
-     */
-    private $writerPartMimetype;
+    private Mimetype $writerPartMimetype;
 
-    /**
-     * @var Settings
-     */
-    private $writerPartSettings;
+    private Settings $writerPartSettings;
 
-    /**
-     * @var Styles
-     */
-    private $writerPartStyles;
+    private Styles $writerPartStyles;
 
-    /**
-     * @var Thumbnails
-     */
-    private $writerPartThumbnails;
+    private Thumbnails $writerPartThumbnails;
 
     /**
      * Create a new Ods.
@@ -146,10 +125,8 @@ public function save($filename, int $flags = 0): void
 
     /**
      * Create zip object.
-     *
-     * @return ZipStream
      */
-    private function createZip()
+    private function createZip(): ZipStream
     {
         // Try opening the ZIP file
         if (!is_resource($this->fileHandle)) {
@@ -177,7 +154,7 @@ public function getSpreadsheet()
      *
      * @return $this
      */
-    public function setSpreadsheet(Spreadsheet $spreadsheet)
+    public function setSpreadsheet(Spreadsheet $spreadsheet): static
     {
         $this->spreadSheet = $spreadsheet;
 
diff --git a/src/PhpSpreadsheet/Writer/Ods/AutoFilters.php b/src/PhpSpreadsheet/Writer/Ods/AutoFilters.php
index 996ec1a545..2debda89d2 100644
--- a/src/PhpSpreadsheet/Writer/Ods/AutoFilters.php
+++ b/src/PhpSpreadsheet/Writer/Ods/AutoFilters.php
@@ -9,15 +9,9 @@
 
 class AutoFilters
 {
-    /**
-     * @var XMLWriter
-     */
-    private $objWriter;
+    private XMLWriter $objWriter;
 
-    /**
-     * @var Spreadsheet
-     */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     public function __construct(XMLWriter $objWriter, Spreadsheet $spreadsheet)
     {
diff --git a/src/PhpSpreadsheet/Writer/Ods/Cell/Style.php b/src/PhpSpreadsheet/Writer/Ods/Cell/Style.php
index 4d46a5e140..0fee9a9648 100644
--- a/src/PhpSpreadsheet/Writer/Ods/Cell/Style.php
+++ b/src/PhpSpreadsheet/Writer/Ods/Cell/Style.php
@@ -19,8 +19,7 @@ class Style
     public const ROW_STYLE_PREFIX = 'ro';
     public const TABLE_STYLE_PREFIX = 'ta';
 
-    /** @var XMLWriter */
-    private $writer;
+    private XMLWriter $writer;
 
     public function __construct(XMLWriter $writer)
     {
diff --git a/src/PhpSpreadsheet/Writer/Ods/Content.php b/src/PhpSpreadsheet/Writer/Ods/Content.php
index 3a5cdbd7a7..de452107d5 100644
--- a/src/PhpSpreadsheet/Writer/Ods/Content.php
+++ b/src/PhpSpreadsheet/Writer/Ods/Content.php
@@ -22,8 +22,7 @@ class Content extends WriterPart
     const NUMBER_COLS_REPEATED_MAX = 1024;
     const NUMBER_ROWS_REPEATED_MAX = 1048576;
 
-    /** @var Formula */
-    private $formulaConvertor;
+    private Formula $formulaConvertor;
 
     /**
      * Set parent Ods writer.
@@ -194,7 +193,7 @@ private function writeCells(XMLWriter $objWriter, RowCellIterator $cells): void
         $numberColsRepeated = self::NUMBER_COLS_REPEATED_MAX;
         $prevColumn = -1;
         foreach ($cells as $cell) {
-            /** @var \PhpOffice\PhpSpreadsheet\Cell\Cell $cell */
+            /** @var Cell $cell */
             $column = Coordinate::columnIndexFromString($cell->getColumn()) - 1;
 
             $this->writeCellSpan($objWriter, $column, $prevColumn);
@@ -289,11 +288,8 @@ private function writeCells(XMLWriter $objWriter, RowCellIterator $cells): void
 
     /**
      * Write span.
-     *
-     * @param int $curColumn
-     * @param int $prevColumn
      */
-    private function writeCellSpan(XMLWriter $objWriter, $curColumn, $prevColumn): void
+    private function writeCellSpan(XMLWriter $objWriter, int $curColumn, int $prevColumn): void
     {
         $diff = $curColumn - $prevColumn - 1;
         if (1 === $diff) {
diff --git a/src/PhpSpreadsheet/Writer/Ods/NamedExpressions.php b/src/PhpSpreadsheet/Writer/Ods/NamedExpressions.php
index e309dab117..6cc5e7555d 100644
--- a/src/PhpSpreadsheet/Writer/Ods/NamedExpressions.php
+++ b/src/PhpSpreadsheet/Writer/Ods/NamedExpressions.php
@@ -10,14 +10,11 @@
 
 class NamedExpressions
 {
-    /** @var XMLWriter */
-    private $objWriter;
+    private XMLWriter $objWriter;
 
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
-    /** @var Formula */
-    private $formulaConvertor;
+    private Formula $formulaConvertor;
 
     public function __construct(XMLWriter $objWriter, Spreadsheet $spreadsheet, Formula $formulaConvertor)
     {
diff --git a/src/PhpSpreadsheet/Writer/Ods/WriterPart.php b/src/PhpSpreadsheet/Writer/Ods/WriterPart.php
index 17d5d16931..67b0f6b717 100644
--- a/src/PhpSpreadsheet/Writer/Ods/WriterPart.php
+++ b/src/PhpSpreadsheet/Writer/Ods/WriterPart.php
@@ -8,10 +8,8 @@ abstract class WriterPart
 {
     /**
      * Parent Ods object.
-     *
-     * @var Ods
      */
-    private $parentWriter;
+    private Ods $parentWriter;
 
     /**
      * Get Ods writer.
diff --git a/src/PhpSpreadsheet/Writer/Pdf.php b/src/PhpSpreadsheet/Writer/Pdf.php
index 493bbba3e5..e74bb8f38a 100644
--- a/src/PhpSpreadsheet/Writer/Pdf.php
+++ b/src/PhpSpreadsheet/Writer/Pdf.php
@@ -11,10 +11,8 @@ abstract class Pdf extends Html
 {
     /**
      * Temporary storage directory.
-     *
-     * @var string
      */
-    protected $tempDir = '';
+    protected string $tempDir;
 
     /**
      * Font.
@@ -25,10 +23,8 @@ abstract class Pdf extends Html
 
     /**
      * Orientation (Over-ride).
-     *
-     * @var ?string
      */
-    protected $orientation;
+    protected ?string $orientation = null;
 
     /**
      * Paper size (Over-ride).
diff --git a/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php b/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php
index d781483eb0..3e9e94ebeb 100644
--- a/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php
+++ b/src/PhpSpreadsheet/Writer/Pdf/Mpdf.php
@@ -91,10 +91,8 @@ public function save($filename, int $flags = 0): void
      * Convert inches to mm.
      *
      * @param float $inches
-     *
-     * @return float
      */
-    private function inchesToMm($inches)
+    private function inchesToMm($inches): float
     {
         return $inches * 25.4;
     }
diff --git a/src/PhpSpreadsheet/Writer/Xls.php b/src/PhpSpreadsheet/Writer/Xls.php
index 25533a3105..d18a44059b 100644
--- a/src/PhpSpreadsheet/Writer/Xls.php
+++ b/src/PhpSpreadsheet/Writer/Xls.php
@@ -31,10 +31,8 @@ class Xls extends BaseWriter
 {
     /**
      * PhpSpreadsheet object.
-     *
-     * @var Spreadsheet
      */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     /**
      * Total number of shared strings in workbook.
@@ -66,10 +64,8 @@ class Xls extends BaseWriter
 
     /**
      * Formula parser.
-     *
-     * @var Parser
      */
-    private $parser;
+    private Parser $parser;
 
     /**
      * Identifier clusters for drawings. Used in MSODRAWINGGROUP record.
@@ -571,10 +567,8 @@ private function buildWorkbookEscher(): void
 
     /**
      * Build the OLE Part for DocumentSummary Information.
-     *
-     * @return string
      */
-    private function writeDocumentSummaryInformation()
+    private function writeDocumentSummaryInformation(): string
     {
         // offset: 0; size: 2; must be 0xFE 0xFF (UTF-16 LE byte order mark)
         $data = pack('v', 0xFFFE);
@@ -812,10 +806,8 @@ private function writeSummaryProp(string $dataProp, int &$dataSection_NumProps,
 
     /**
      * Build the OLE Part for Summary Information.
-     *
-     * @return string
      */
-    private function writeSummaryInformation()
+    private function writeSummaryInformation(): string
     {
         // offset: 0; size: 2; must be 0xFE 0xFF (UTF-16 LE byte order mark)
         $data = pack('v', 0xFFFE);
diff --git a/src/PhpSpreadsheet/Writer/Xls/ConditionalHelper.php b/src/PhpSpreadsheet/Writer/Xls/ConditionalHelper.php
index 0f78b8c5df..0ef7e9a367 100644
--- a/src/PhpSpreadsheet/Writer/Xls/ConditionalHelper.php
+++ b/src/PhpSpreadsheet/Writer/Xls/ConditionalHelper.php
@@ -9,10 +9,8 @@ class ConditionalHelper
 {
     /**
      * Formula parser.
-     *
-     * @var Parser
      */
-    protected $parser;
+    protected Parser $parser;
 
     /**
      * @var mixed
@@ -24,15 +22,9 @@ class ConditionalHelper
      */
     protected $cellRange;
 
-    /**
-     * @var null|string
-     */
-    protected $tokens;
+    protected ?string $tokens = null;
 
-    /**
-     * @var int
-     */
-    protected $size;
+    protected int $size;
 
     public function __construct(Parser $parser)
     {
diff --git a/src/PhpSpreadsheet/Writer/Xls/Font.php b/src/PhpSpreadsheet/Writer/Xls/Font.php
index 1923200dbd..e3b7923a48 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Font.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Font.php
@@ -8,17 +8,13 @@ class Font
 {
     /**
      * Color index.
-     *
-     * @var int
      */
-    private $colorIndex;
+    private int $colorIndex;
 
     /**
      * Font.
-     *
-     * @var \PhpOffice\PhpSpreadsheet\Style\Font
      */
-    private $font;
+    private \PhpOffice\PhpSpreadsheet\Style\Font $font;
 
     /**
      * Constructor.
@@ -44,10 +40,8 @@ public function setColorIndex($colorIndex): void
 
     /**
      * Get font record data.
-     *
-     * @return string
      */
-    public function writeFont()
+    public function writeFont(): string
     {
         $font_outline = self::$notImplemented;
         $font_shadow = self::$notImplemented;
diff --git a/src/PhpSpreadsheet/Writer/Xls/Parser.php b/src/PhpSpreadsheet/Writer/Xls/Parser.php
index f195ac782b..dd7d585e00 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Parser.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Parser.php
@@ -63,10 +63,8 @@ class Parser
 
     /**
      * The formula to parse.
-     *
-     * @var string
      */
-    private $formula;
+    private string $formula;
 
     /**
      * The character ahead of the current char.
@@ -84,10 +82,8 @@ class Parser
 
     /**
      * Array of external sheets.
-     *
-     * @var array
      */
-    private $externalSheets;
+    private array $externalSheets;
 
     /**
      * Array of sheet references in the form of REF structures.
@@ -469,8 +465,7 @@ class Parser
         'BAHTTEXT' => [368, 1, 0, 0],
     ];
 
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     /**
      * The class constructor.
@@ -491,11 +486,11 @@ public function __construct(Spreadsheet $spreadsheet)
     /**
      * Convert a token to the proper ptg value.
      *
-     * @param mixed $token the token to convert
+     * @param string $token the token to convert
      *
-     * @return mixed the converted token on success
+     * @return string the converted token on success
      */
-    private function convert($token)
+    private function convert(string $token): string
     {
         if (preg_match('/"([^"]|""){0,255}"/', $token)) {
             return $this->convertString($token);
@@ -562,10 +557,8 @@ private function convert($token)
      * Convert a number token to ptgInt or ptgNum.
      *
      * @param mixed $num an integer or double for conversion to its ptg value
-     *
-     * @return string
      */
-    private function convertNumber($num)
+    private function convertNumber($num): string
     {
         // Integer in the range 0..2**16-1
         if ((preg_match('/^\\d+$/', $num)) && ($num <= 65535)) {
@@ -590,9 +583,9 @@ private function convertBool(int $num): string
      *
      * @param string $string a string for conversion to its ptg value
      *
-     * @return mixed the converted token on success
+     * @return string the converted token
      */
-    private function convertString($string)
+    private function convertString($string): string
     {
         // chop away beggining and ending quotes
         $string = substr($string, 1, -1);
@@ -612,7 +605,7 @@ private function convertString($string)
      *
      * @return string The packed ptg for the function
      */
-    private function convertFunction($token, $num_args)
+    private function convertFunction($token, $num_args): string
     {
         $args = $this->functions[$token][1];
 
@@ -630,10 +623,8 @@ private function convertFunction($token, $num_args)
      *
      * @param string $range An Excel range in the A1:A2
      * @param int $class
-     *
-     * @return string
      */
-    private function convertRange2d($range, $class = 0)
+    private function convertRange2d($range, $class = 0): string
     {
         // TODO: possible class value 0,1,2 check Formula.pm
         // Split the range into 2 cell refs
@@ -668,18 +659,18 @@ private function convertRange2d($range, $class = 0)
      *
      * @param string $token an Excel range in the Sheet1!A1:A2 format
      *
-     * @return mixed the packed ptgArea3d token on success
+     * @return string the packed ptgArea3d token on success
      */
-    private function convertRange3d($token)
+    private function convertRange3d($token): string
     {
         // Split the ref at the ! symbol
         [$ext_ref, $range] = PhpspreadsheetWorksheet::extractSheetTitle($token, true);
 
         // Convert the external reference part (different for BIFF8)
-        $ext_ref = $this->getRefIndex($ext_ref);
+        $ext_ref = $this->getRefIndex($ext_ref ?? '');
 
         // Split the range into 2 cell refs
-        [$cell1, $cell2] = explode(':', $range);
+        [$cell1, $cell2] = explode(':', $range ?? '');
 
         // Convert the cell references
         if (preg_match('/^(\$)?[A-Ia-i]?[A-Za-z](\$)?(\\d+)$/', $cell1)) {
@@ -702,7 +693,7 @@ private function convertRange3d($token)
      *
      * @return string The cell in packed() format with the corresponding ptg
      */
-    private function convertRef2d($cell)
+    private function convertRef2d($cell): string
     {
         // Convert the cell reference
         $cell_array = $this->cellToPackedRowcol($cell);
@@ -720,18 +711,18 @@ private function convertRef2d($cell)
      *
      * @param string $cell An Excel cell reference
      *
-     * @return mixed the packed ptgRef3d token on success
+     * @return string the packed ptgRef3d token on success
      */
-    private function convertRef3d($cell)
+    private function convertRef3d($cell): string
     {
         // Split the ref at the ! symbol
         [$ext_ref, $cell] = PhpspreadsheetWorksheet::extractSheetTitle($cell, true);
 
         // Convert the external reference part (different for BIFF8)
-        $ext_ref = $this->getRefIndex($ext_ref);
+        $ext_ref = $this->getRefIndex($ext_ref ?? '');
 
         // Convert the cell reference part
-        [$row, $col] = $this->cellToPackedRowcol($cell);
+        [$row, $col] = $this->cellToPackedRowcol($cell ?? '');
 
         // The ptg value depends on the class of the ptg.
         $ptgRef = pack('C', $this->ptg['ptgRef3dA']);
@@ -746,7 +737,7 @@ private function convertRef3d($cell)
      *
      * @return string The error code ptgErr
      */
-    private function convertError($errorCode)
+    private function convertError($errorCode): string
     {
         switch ($errorCode) {
             case '#NULL!':
@@ -803,9 +794,9 @@ private function convertDefinedName(string $name): string
      *
      * @param string $ext_ref The name of the external reference
      *
-     * @return mixed The reference index in packed() format on success
+     * @return string The reference index in packed() format on success
      */
-    private function getRefIndex($ext_ref)
+    private function getRefIndex($ext_ref): string
     {
         $ext_ref = (string) preg_replace(["/^'/", "/'$/"], ['', ''], $ext_ref); // Remove leading and trailing ' if any.
         $ext_ref = str_replace('\'\'', '\'', $ext_ref); // Replace escaped '' with '
@@ -865,7 +856,7 @@ private function getRefIndex($ext_ref)
      *
      * @return int The sheet index, -1 if the sheet was not found
      */
-    private function getSheetIndex($sheet_name)
+    private function getSheetIndex(string $sheet_name)
     {
         if (!isset($this->externalSheets[$sheet_name])) {
             return -1;
@@ -882,7 +873,7 @@ private function getSheetIndex($sheet_name)
      * @param string $name The name of the worksheet being added
      * @param int $index The index of the worksheet being added
      *
-     * @see \PhpOffice\PhpSpreadsheet\Writer\Xls\Workbook::addWorksheet()
+     * @see Workbook::addWorksheet
      */
     public function setExtSheet($name, $index): void
     {
@@ -896,7 +887,7 @@ public function setExtSheet($name, $index): void
      *
      * @return array Array containing the row and column in packed() format
      */
-    private function cellToPackedRowcol($cell)
+    private function cellToPackedRowcol($cell): array
     {
         $cell = strtoupper($cell);
         [$row, $col, $row_rel, $col_rel] = $this->cellToRowcol($cell);
@@ -925,7 +916,7 @@ private function cellToPackedRowcol($cell)
      *
      * @return array Array containing (row1,col1,row2,col2) in packed() format
      */
-    private function rangeToPackedRange($range)
+    private function rangeToPackedRange(string $range): array
     {
         preg_match('/(\$)?(\d+)\:(\$)?(\d+)/', $range, $match);
         // return absolute rows if there is a $ in the ref
@@ -963,10 +954,8 @@ private function rangeToPackedRange($range)
      * whether the row or column are relative references.
      *
      * @param string $cell the Excel cell reference in A1 format
-     *
-     * @return array
      */
-    private function cellToRowcol($cell)
+    private function cellToRowcol(string $cell): array
     {
         preg_match('/(\$)?([A-I]?[A-Z])(\$)?(\d+)/', $cell, $match);
         // return absolute column if there is a $ in the ref
@@ -1034,17 +1023,16 @@ private function advance(): void
             }
             ++$i;
         }
-        //die("Lexical error ".$this->currentCharacter);
     }
 
     /**
      * Checks if it's a valid token.
      *
-     * @param mixed $token the token to check
+     * @param string $token the token to check
      *
-     * @return mixed The checked token or false on failure
+     * @return string The checked token or empty string on failure
      */
-    private function match($token)
+    private function match(string $token): string
     {
         switch ($token) {
             case '+':
@@ -1144,9 +1132,9 @@ private function match($token)
      * @param string $formula the formula to parse, without the initial equal
      *                        sign (=)
      *
-     * @return mixed true on success
+     * @return bool true on success
      */
-    public function parse($formula)
+    public function parse($formula): bool
     {
         $this->currentCharacter = 0;
         $this->formula = (string) $formula;
@@ -1273,7 +1261,7 @@ private function expression()
      *
      * @see fact()
      */
-    private function parenthesizedExpression()
+    private function parenthesizedExpression(): array
     {
         return $this->createTree('ptgParen', $this->expression(), '');
     }
@@ -1461,7 +1449,7 @@ private function func()
      *
      * @return array A tree
      */
-    private function createTree($value, $left, $right)
+    private function createTree($value, $left, $right): array
     {
         return ['value' => $value, 'left' => $left, 'right' => $right];
     }
@@ -1493,7 +1481,7 @@ private function createTree($value, $left, $right)
      *
      * @return string The tree in reverse polish notation
      */
-    public function toReversePolish($tree = [])
+    public function toReversePolish($tree = []): string
     {
         $polish = ''; // the string we are going to return
         if (empty($tree)) { // If it's the first call use parseTree
diff --git a/src/PhpSpreadsheet/Writer/Xls/Workbook.php b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
index 3c68847aa9..329279f16e 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
@@ -49,24 +49,20 @@ class Workbook extends BIFFwriter
 {
     /**
      * Formula parser.
-     *
-     * @var \PhpOffice\PhpSpreadsheet\Writer\Xls\Parser
      */
-    private $parser;
+    private Parser $parser;
 
     /**
      * The BIFF file size for the workbook. Not currently used.
      *
-     * @var int
-     *
      * @see calcSheetOffsets()
      */
-    private $biffSize; // @phpstan-ignore-line
+    private int $biffSize; // @phpstan-ignore-line
 
     /**
      * XF Writers.
      *
-     * @var \PhpOffice\PhpSpreadsheet\Writer\Xls\Xf[]
+     * @var Xf[]
      */
     private $xfWriters = [];
 
@@ -79,24 +75,18 @@ class Workbook extends BIFFwriter
 
     /**
      * The codepage indicates the text encoding used for strings.
-     *
-     * @var int
      */
-    private $codepage;
+    private int $codepage;
 
     /**
      * The country code used for localization.
-     *
-     * @var int
      */
-    private $countryCode;
+    private int $countryCode;
 
     /**
      * Workbook.
-     *
-     * @var Spreadsheet
      */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     /**
      * Fonts writers.
@@ -170,10 +160,8 @@ class Workbook extends BIFFwriter
 
     /**
      * Escher object corresponding to MSODRAWINGGROUP.
-     *
-     * @var null|\PhpOffice\PhpSpreadsheet\Shared\Escher
      */
-    private $escher;
+    private ?\PhpOffice\PhpSpreadsheet\Shared\Escher $escher = null;
 
     /** @var mixed */
     private static $scrutinizerFalse = false;
@@ -233,7 +221,7 @@ public function __construct(Spreadsheet $spreadsheet, &$str_total, &$str_unique,
      *
      * @return int Index to XF record
      */
-    public function addXfWriter(Style $style, $isStyleXf = false)
+    public function addXfWriter(Style $style, $isStyleXf = false): int
     {
         $xfWriter = new Xf($style);
         $xfWriter->setIsStyleXf($isStyleXf);
@@ -417,7 +405,7 @@ private function setPaletteXl97(): void
      *
      * @return string Binary data for workbook stream
      */
-    public function writeWorkbook(array $worksheetSizes)
+    public function writeWorkbook(array $worksheetSizes): string
     {
         $this->worksheetSizes = $worksheetSizes;
 
@@ -731,7 +719,7 @@ private function writeAllDefinedNamesBiff8(): string
      *
      * @return string Complete binary record data
      */
-    private function writeDefinedNameBiff8($name, $formulaData, $sheetIndex = 0, $isBuiltIn = false)
+    private function writeDefinedNameBiff8($name, string $formulaData, int $sheetIndex = 0, bool $isBuiltIn = false): string
     {
         $record = 0x0018;
 
@@ -760,14 +748,12 @@ private function writeDefinedNameBiff8($name, $formulaData, $sheetIndex = 0, $is
     /**
      * Write a short NAME record.
      *
-     * @param string $name
      * @param int $sheetIndex 1-based sheet index the defined name applies to. 0 = global
      * @param int[][] $rangeBounds range boundaries
-     * @param bool $isHidden
      *
      * @return string Complete binary record data
      * */
-    private function writeShortNameBiff8($name, $sheetIndex, $rangeBounds, $isHidden = false)
+    private function writeShortNameBiff8(string $name, int $sheetIndex, array $rangeBounds, bool $isHidden = false): string
     {
         $record = 0x0018;
 
@@ -941,7 +927,7 @@ private function writeStyle(): void
      * @param string $format Custom format string
      * @param int $ifmt Format index code
      */
-    private function writeNumberFormat($format, $ifmt): void
+    private function writeNumberFormat(string $format, $ifmt): void
     {
         $record = 0x041E; // Record identifier
 
@@ -1042,7 +1028,7 @@ private function writePalette(): void
      *
      * @return string Binary data
      */
-    private function writeSharedStringsTable()
+    private function writeSharedStringsTable(): string
     {
         // maximum size of record data (excluding record header)
         $continue_limit = 8224;
diff --git a/src/PhpSpreadsheet/Writer/Xls/Worksheet.php b/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
index aeedd08e77..c2aedbbab1 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Worksheet.php
@@ -12,7 +12,6 @@
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
 use PhpOffice\PhpSpreadsheet\Shared\Xls;
 use PhpOffice\PhpSpreadsheet\Style\Border;
-use PhpOffice\PhpSpreadsheet\Style\Color;
 use PhpOffice\PhpSpreadsheet\Style\Conditional;
 use PhpOffice\PhpSpreadsheet\Style\Protection;
 use PhpOffice\PhpSpreadsheet\Worksheet\PageSetup;
@@ -63,10 +62,8 @@ class Worksheet extends BIFFwriter
 
     /**
      * Formula parser.
-     *
-     * @var \PhpOffice\PhpSpreadsheet\Writer\Xls\Parser
      */
-    private $parser;
+    private Parser $parser;
 
     /**
      * Array containing format information for columns.
@@ -77,40 +74,30 @@ class Worksheet extends BIFFwriter
 
     /**
      * The active pane for the worksheet.
-     *
-     * @var int
      */
-    private $activePane;
+    private int $activePane;
 
     /**
      * Whether to use outline.
-     *
-     * @var bool
      */
-    private $outlineOn;
+    private bool $outlineOn;
 
     /**
      * Auto outline styles.
-     *
-     * @var bool
      */
-    private $outlineStyle;
+    private bool $outlineStyle;
 
     /**
      * Whether to have outline summary below.
      * Not currently used.
-     *
-     * @var bool
      */
-    private $outlineBelow; //* @phpstan-ignore-line
+    private bool $outlineBelow; //* @phpstan-ignore-line
 
     /**
      * Whether to have outline summary at the right.
      * Not currently used.
-     *
-     * @var bool
      */
-    private $outlineRight; //* @phpstan-ignore-line
+    private bool $outlineRight; //* @phpstan-ignore-line
 
     /**
      * Reference to the total number of strings in the workbook.
@@ -142,31 +129,23 @@ class Worksheet extends BIFFwriter
 
     /**
      * Index of first used row (at least 0).
-     *
-     * @var int
      */
-    private $firstRowIndex;
+    private int $firstRowIndex;
 
     /**
      * Index of last used row. (no used rows means -1).
-     *
-     * @var int
      */
-    private $lastRowIndex;
+    private int $lastRowIndex;
 
     /**
      * Index of first used column (at least 0).
-     *
-     * @var int
      */
-    private $firstColumnIndex;
+    private int $firstColumnIndex;
 
     /**
      * Index of last used column (no used columns means -1).
-     *
-     * @var int
      */
-    private $lastColumnIndex;
+    private int $lastColumnIndex;
 
     /**
      * Sheet object.
@@ -177,10 +156,8 @@ class Worksheet extends BIFFwriter
 
     /**
      * Escher object corresponding to MSODRAWING.
-     *
-     * @var null|\PhpOffice\PhpSpreadsheet\Shared\Escher
      */
-    private $escher;
+    private ?\PhpOffice\PhpSpreadsheet\Shared\Escher $escher = null;
 
     /**
      * Array of font hashes associated to FONT records index.
@@ -194,10 +171,7 @@ class Worksheet extends BIFFwriter
      */
     private $preCalculateFormulas;
 
-    /**
-     * @var int
-     */
-    private $printHeaders;
+    private int $printHeaders;
 
     /**
      * Constructor.
@@ -259,7 +233,7 @@ public function __construct(&$str_total, &$str_unique, &$str_table, &$colors, Pa
      * Add data to the beginning of the workbook (note the reverse order)
      * and to the end of the workbook.
      *
-     * @see \PhpOffice\PhpSpreadsheet\Writer\Xls\Workbook::storeWorkbook()
+     * @see Workbook::storeWorkbook
      */
     public function close(): void
     {
@@ -584,7 +558,7 @@ private function writeConditionalFormatting(): void
      *
      * @return string Binary data
      */
-    private function writeBIFF8CellRangeAddressFixed($range)
+    private function writeBIFF8CellRangeAddressFixed($range): string
     {
         $explodes = explode(':', $range);
 
@@ -662,11 +636,9 @@ public function setOutline($visible = true, $symbols_below = true, $symbols_righ
      * @param int $row Zero indexed row
      * @param int $col Zero indexed column
      * @param float $num The number to write
-     * @param mixed $xfIndex The optional XF format
-     *
-     * @return int
+     * @param int $xfIndex The optional XF format
      */
-    private function writeNumber($row, $col, $num, $xfIndex)
+    private function writeNumber(int $row, int $col, $num, int $xfIndex): int
     {
         $record = 0x0203; // Record identifier
         $length = 0x000E; // Number of bytes to follow
@@ -691,7 +663,7 @@ private function writeNumber($row, $col, $num, $xfIndex)
      * @param string $str The string
      * @param int $xfIndex Index to XF record
      */
-    private function writeString($row, $col, $str, $xfIndex): void
+    private function writeString(int $row, int $col, $str, int $xfIndex): void
     {
         $this->writeLabelSst($row, $col, $str, $xfIndex);
     }
@@ -706,7 +678,7 @@ private function writeString($row, $col, $str, $xfIndex): void
      * @param int $xfIndex The XF format index for the cell
      * @param array $arrcRun Index to Font record and characters beginning
      */
-    private function writeRichTextString($row, $col, $str, $xfIndex, $arrcRun): void
+    private function writeRichTextString(int $row, int $col, string $str, int $xfIndex, array $arrcRun): void
     {
         $record = 0x00FD; // Record identifier
         $length = 0x000A; // Bytes to follow
@@ -731,9 +703,9 @@ private function writeRichTextString($row, $col, $str, $xfIndex, $arrcRun): void
      * @param int $row Zero indexed row
      * @param int $col Zero indexed column
      * @param string $str The string to write
-     * @param mixed $xfIndex The XF format index for the cell
+     * @param int $xfIndex The XF format index for the cell
      */
-    private function writeLabelSst($row, $col, $str, $xfIndex): void
+    private function writeLabelSst(int $row, int $col, $str, int $xfIndex): void
     {
         $record = 0x00FD; // Record identifier
         $length = 0x000A; // Bytes to follow
@@ -765,11 +737,9 @@ private function writeLabelSst($row, $col, $str, $xfIndex): void
      *
      * @param int $row Zero indexed row
      * @param int $col Zero indexed column
-     * @param mixed $xfIndex The XF format index
-     *
-     * @return int
+     * @param int $xfIndex The XF format index
      */
-    public function writeBlank($row, $col, $xfIndex)
+    public function writeBlank($row, $col, $xfIndex): int
     {
         $record = 0x0201; // Record identifier
         $length = 0x0006; // Number of bytes to follow
@@ -788,11 +758,8 @@ public function writeBlank($row, $col, $xfIndex)
      * @param int $col Column index (0-based)
      * @param int $value
      * @param int $isError Error or Boolean?
-     * @param int $xfIndex
-     *
-     * @return int
      */
-    private function writeBoolErr($row, $col, $value, $isError, $xfIndex)
+    private function writeBoolErr(int $row, int $col, $value, int $isError, int $xfIndex): int
     {
         $record = 0x0205;
         $length = 8;
@@ -835,12 +802,12 @@ public static function getAllowThrow(): bool
      * @param int $row Zero indexed row
      * @param int $col Zero indexed column
      * @param string $formula The formula text string
-     * @param mixed $xfIndex The XF format index
+     * @param int $xfIndex The XF format index
      * @param mixed $calculatedValue Calculated value
      *
      * @return int
      */
-    private function writeFormula($row, $col, $formula, $xfIndex, $calculatedValue)
+    private function writeFormula(int $row, int $col, string $formula, int $xfIndex, $calculatedValue)
     {
         $record = 0x0006; // Record identifier
         // Initialize possible additional value for STRING record that should be written after the FORMULA record?
@@ -922,10 +889,8 @@ private function writeFormula($row, $col, $formula, $xfIndex, $calculatedValue)
 
     /**
      * Write a STRING record. This.
-     *
-     * @param string $stringValue
      */
-    private function writeStringRecord($stringValue): void
+    private function writeStringRecord(string $stringValue): void
     {
         $record = 0x0207; // Record identifier
         $data = StringHelper::UTF8toBIFF8UnicodeLong($stringValue);
@@ -951,7 +916,7 @@ private function writeStringRecord($stringValue): void
      * @param int $col Column
      * @param string $url URL string
      */
-    private function writeUrl($row, $col, $url): void
+    private function writeUrl(int $row, int $col, $url): void
     {
         // Add start row and col to arg list
         $this->writeUrlRange($row, $col, $row, $col, $url);
@@ -971,7 +936,7 @@ private function writeUrl($row, $col, $url): void
      *
      * @see writeUrl()
      */
-    private function writeUrlRange($row1, $col1, $row2, $col2, $url): void
+    private function writeUrlRange(int $row1, int $col1, int $row2, int $col2, $url): void
     {
         // Check for internal/external sheet links or default to web link
         if (preg_match('[^internal:]', $url)) {
@@ -1039,7 +1004,7 @@ public function writeUrlWeb($row1, $col1, $row2, $col2, $url): void
      *
      * @see writeUrl()
      */
-    private function writeUrlInternal($row1, $col1, $row2, $col2, $url): void
+    private function writeUrlInternal(int $row1, int $col1, int $row2, int $col2, $url): void
     {
         $record = 0x01B8; // Record identifier
 
@@ -1087,7 +1052,7 @@ private function writeUrlInternal($row1, $col1, $row2, $col2, $url): void
      *
      * @see writeUrl()
      */
-    private function writeUrlExternal($row1, $col1, $row2, $col2, $url): void
+    private function writeUrlExternal(int $row1, int $col1, int $row2, int $col2, $url): void
     {
         // Network drives are different. We will handle them separately
         // MS/Novell network drives and shares start with \\
@@ -1178,7 +1143,7 @@ private function writeUrlExternal($row1, $col1, $row2, $col2, $url): void
      * @param bool $hidden The optional hidden attribute
      * @param int $level The optional outline level for row, in range [0,7]
      */
-    private function writeRow($row, $height, $xfIndex, $hidden = false, $level = 0): void
+    private function writeRow(int $row, int $height, int $xfIndex, bool $hidden = false, $level = 0): void
     {
         $record = 0x0208; // Record identifier
         $length = 0x0010; // Number of bytes to follow
@@ -2184,17 +2149,17 @@ private function writePassword(): void
      *
      * @param int $row The row we are going to insert the bitmap into
      * @param int $col The column we are going to insert the bitmap into
-     * @param mixed $bitmap The bitmap filename or GD-image resource
+     * @param GdImage|string $bitmap The bitmap filename or GD-image resource
      * @param int $x the horizontal position (offset) of the image inside the cell
      * @param int $y the vertical position (offset) of the image inside the cell
      * @param float $scale_x The horizontal scale
      * @param float $scale_y The vertical scale
      */
-    public function insertBitmap($row, $col, $bitmap, $x = 0, $y = 0, $scale_x = 1, $scale_y = 1): void
+    public function insertBitmap($row, $col, GdImage|string $bitmap, $x = 0, $y = 0, $scale_x = 1, $scale_y = 1): void
     {
-        $bitmap_array = (is_resource($bitmap) || $bitmap instanceof GdImage
+        $bitmap_array = $bitmap instanceof GdImage
             ? $this->processBitmapGd($bitmap)
-            : $this->processBitmap($bitmap));
+            : $this->processBitmap($bitmap);
         [$width, $height, $size, $data] = $bitmap_array;
 
         // Scale the frame of the image.
@@ -2332,7 +2297,7 @@ public function positionImage($col_start, $row_start, $x1, $y1, $width, $height)
      * @param int $rwB Row containing bottom right corner of object
      * @param int $dyB Distance from bottom of cell
      */
-    private function writeObjPicture($colL, $dxL, $rwT, $dyT, $colR, $dxR, $rwB, $dyB): void
+    private function writeObjPicture(int $colL, int $dxL, int $rwT, int|float $dyT, int $colR, int $dxR, int $rwB, int $dyB): void
     {
         $record = 0x005d; // Record identifier
         $length = 0x003c; // Bytes to follow
@@ -2400,11 +2365,11 @@ private function writeObjPicture($colL, $dxL, $rwT, $dyT, $colR, $dxR, $rwB, $dy
     /**
      * Convert a GD-image into the internal format.
      *
-     * @param GdImage|resource $image The image to process
+     * @param GdImage $image The image to process
      *
      * @return array Array with data and properties of the bitmap
      */
-    public function processBitmapGd($image)
+    public function processBitmapGd(GdImage $image): array
     {
         $width = imagesx($image);
         $height = imagesy($image);
@@ -2438,7 +2403,7 @@ public function processBitmapGd($image)
      *
      * @return array Array with data and properties of the bitmap
      */
-    public function processBitmap($bitmap)
+    public function processBitmap($bitmap): array
     {
         // Open file.
         $bmp_fd = @fopen($bitmap, 'rb');
diff --git a/src/PhpSpreadsheet/Writer/Xls/Xf.php b/src/PhpSpreadsheet/Writer/Xls/Xf.php
index 7ac26665cb..3560031883 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Xf.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Xf.php
@@ -48,85 +48,58 @@ class Xf
 {
     /**
      * Style XF or a cell XF ?
-     *
-     * @var bool
      */
-    private $isStyleXf;
+    private bool $isStyleXf;
 
     /**
      * Index to the FONT record. Index 4 does not exist.
-     *
-     * @var int
      */
-    private $fontIndex;
+    private int $fontIndex;
 
     /**
      * An index (2 bytes) to a FORMAT record (number format).
-     *
-     * @var int
      */
-    private $numberFormatIndex;
+    private int $numberFormatIndex;
 
     /**
      * 1 bit, apparently not used.
-     *
-     * @var int
      */
-    private $textJustLast;
+    private int $textJustLast;
 
     /**
      * The cell's foreground color.
-     *
-     * @var int
      */
-    private $foregroundColor;
+    private int $foregroundColor;
 
     /**
      * The cell's background color.
-     *
-     * @var int
      */
-    private $backgroundColor;
+    private int $backgroundColor;
 
     /**
      * Color of the bottom border of the cell.
-     *
-     * @var int
      */
-    private $bottomBorderColor;
+    private int $bottomBorderColor;
 
     /**
      * Color of the top border of the cell.
-     *
-     * @var int
      */
-    private $topBorderColor;
+    private int $topBorderColor;
 
     /**
      * Color of the left border of the cell.
-     *
-     * @var int
      */
-    private $leftBorderColor;
+    private int $leftBorderColor;
 
     /**
      * Color of the right border of the cell.
-     *
-     * @var int
      */
-    private $rightBorderColor;
+    private int $rightBorderColor;
 
     //private $diag; // theoretically int, not yet implemented
+    private int $diagColor;
 
-    /**
-     * @var int
-     */
-    private $diagColor;
-
-    /**
-     * @var Style
-     */
-    private $style;
+    private Style $style;
 
     /**
      * Constructor.
@@ -160,7 +133,7 @@ public function __construct(Style $style)
      *
      * @return string The XF record
      */
-    public function writeXf()
+    public function writeXf(): string
     {
         // Set the type of the XF record and some of the attributes.
         if ($this->isStyleXf) {
@@ -386,13 +359,11 @@ private static function mapTextRotation($textRotation)
     /**
      * Map locked values.
      *
-     * @param string $locked
-     *
-     * @return int
+     * @param ?string $locked
      */
-    private static function mapLocked($locked)
+    private static function mapLocked($locked): int
     {
-        return array_key_exists($locked, self::LOCK_ARRAY) ? self::LOCK_ARRAY[$locked] : 1;
+        return $locked !== null && array_key_exists($locked, self::LOCK_ARRAY) ? self::LOCK_ARRAY[$locked] : 1;
     }
 
     private const HIDDEN_ARRAY = [
@@ -404,12 +375,10 @@ private static function mapLocked($locked)
     /**
      * Map hidden.
      *
-     * @param string $hidden
-     *
-     * @return int
+     * @param ?string $hidden
      */
-    private static function mapHidden($hidden)
+    private static function mapHidden($hidden): int
     {
-        return array_key_exists($hidden, self::HIDDEN_ARRAY) ? self::HIDDEN_ARRAY[$hidden] : 0;
+        return $hidden !== null && array_key_exists($hidden, self::HIDDEN_ARRAY) ? self::HIDDEN_ARRAY[$hidden] : 0;
     }
 }
diff --git a/src/PhpSpreadsheet/Writer/Xlsx.php b/src/PhpSpreadsheet/Writer/Xlsx.php
index 6ed12d4aa1..e49cb8d76e 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx.php
@@ -61,49 +61,49 @@ class Xlsx extends BaseWriter
      *
      * @var HashTable<Conditional>
      */
-    private $stylesConditionalHashTable;
+    private HashTable $stylesConditionalHashTable;
 
     /**
      * Private unique Style HashTable.
      *
      * @var HashTable<\PhpOffice\PhpSpreadsheet\Style\Style>
      */
-    private $styleHashTable;
+    private HashTable $styleHashTable;
 
     /**
      * Private unique Fill HashTable.
      *
      * @var HashTable<Fill>
      */
-    private $fillHashTable;
+    private HashTable $fillHashTable;
 
     /**
      * Private unique \PhpOffice\PhpSpreadsheet\Style\Font HashTable.
      *
      * @var HashTable<Font>
      */
-    private $fontHashTable;
+    private HashTable $fontHashTable;
 
     /**
      * Private unique Borders HashTable.
      *
      * @var HashTable<Borders>
      */
-    private $bordersHashTable;
+    private HashTable $bordersHashTable;
 
     /**
      * Private unique NumberFormat HashTable.
      *
      * @var HashTable<NumberFormat>
      */
-    private $numFmtHashTable;
+    private HashTable $numFmtHashTable;
 
     /**
      * Private unique \PhpOffice\PhpSpreadsheet\Worksheet\Worksheet\BaseDrawing HashTable.
      *
      * @var HashTable<BaseDrawing>
      */
-    private $drawingHashTable;
+    private HashTable $drawingHashTable;
 
     /**
      * Private handle for zip stream.
@@ -112,75 +112,33 @@ class Xlsx extends BaseWriter
      */
     private $zip;
 
-    /**
-     * @var Chart
-     */
-    private $writerPartChart;
+    private Chart $writerPartChart;
 
-    /**
-     * @var Comments
-     */
-    private $writerPartComments;
+    private Comments $writerPartComments;
 
-    /**
-     * @var ContentTypes
-     */
-    private $writerPartContentTypes;
+    private ContentTypes $writerPartContentTypes;
 
-    /**
-     * @var DocProps
-     */
-    private $writerPartDocProps;
+    private DocProps $writerPartDocProps;
 
-    /**
-     * @var Drawing
-     */
-    private $writerPartDrawing;
+    private Drawing $writerPartDrawing;
 
-    /**
-     * @var Rels
-     */
-    private $writerPartRels;
+    private Rels $writerPartRels;
 
-    /**
-     * @var RelsRibbon
-     */
-    private $writerPartRelsRibbon;
+    private RelsRibbon $writerPartRelsRibbon;
 
-    /**
-     * @var RelsVBA
-     */
-    private $writerPartRelsVBA;
+    private RelsVBA $writerPartRelsVBA;
 
-    /**
-     * @var StringTable
-     */
-    private $writerPartStringTable;
+    private StringTable $writerPartStringTable;
 
-    /**
-     * @var Style
-     */
-    private $writerPartStyle;
+    private Style $writerPartStyle;
 
-    /**
-     * @var Theme
-     */
-    private $writerPartTheme;
+    private Theme $writerPartTheme;
 
-    /**
-     * @var Table
-     */
-    private $writerPartTable;
+    private Table $writerPartTable;
 
-    /**
-     * @var Workbook
-     */
-    private $writerPartWorkbook;
+    private Workbook $writerPartWorkbook;
 
-    /**
-     * @var Worksheet
-     */
-    private $writerPartWorksheet;
+    private Worksheet $writerPartWorksheet;
 
     /**
      * Create a new Xlsx Writer.
@@ -576,7 +534,7 @@ public function getSpreadsheet()
      *
      * @return $this
      */
-    public function setSpreadsheet(Spreadsheet $spreadsheet)
+    public function setSpreadsheet(Spreadsheet $spreadsheet): static
     {
         $this->spreadSheet = $spreadsheet;
 
@@ -680,7 +638,7 @@ public function getOffice2003Compatibility()
      *
      * @return $this
      */
-    public function setOffice2003Compatibility($office2003compatibility)
+    public function setOffice2003Compatibility($office2003compatibility): static
     {
         $this->office2003compatibility = $office2003compatibility;
 
@@ -705,10 +663,7 @@ private function addZipFiles(array $zipContent): void
         }
     }
 
-    /**
-     * @return mixed
-     */
-    private function processDrawing(WorksheetDrawing $drawing)
+    private function processDrawing(WorksheetDrawing $drawing): string|null|false
     {
         $data = null;
         $filename = $drawing->getPath();
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
index 6d302aac4a..b4733dc43b 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Chart.php
@@ -506,11 +506,9 @@ private function writeDataLabels(XMLWriter $objWriter, ?Layout $chartLayout = nu
     /**
      * Write Category Axis.
      *
-     * @param string $id1
-     * @param string $id2
      * @param bool $isMultiLevelSeries
      */
-    private function writeCategoryAxis(XMLWriter $objWriter, ?Title $xAxisLabel, $id1, $id2, $isMultiLevelSeries, Axis $yAxis): void
+    private function writeCategoryAxis(XMLWriter $objWriter, ?Title $xAxisLabel, string $id1, string $id2, $isMultiLevelSeries, Axis $yAxis): void
     {
         // N.B. writeCategoryAxis may be invoked with the last parameter($yAxis) using $xAxis for ScatterChart, etc
         // In that case, xAxis may contain values like the yAxis, or it may be a date axis (LINECHART).
@@ -726,11 +724,9 @@ private function writeCategoryAxis(XMLWriter $objWriter, ?Title $xAxisLabel, $id
      * Write Value Axis.
      *
      * @param null|string $groupType Chart type
-     * @param string $id1
-     * @param string $id2
      * @param bool $isMultiLevelSeries
      */
-    private function writeValueAxis(XMLWriter $objWriter, ?Title $yAxisLabel, $groupType, $id1, $id2, $isMultiLevelSeries, Axis $xAxis): void
+    private function writeValueAxis(XMLWriter $objWriter, ?Title $yAxisLabel, $groupType, string $id1, string $id2, $isMultiLevelSeries, Axis $xAxis): void
     {
         $objWriter->startElement('c:' . Axis::AXIS_TYPE_VALUE);
         $majorGridlines = $xAxis->getMajorGridlines();
@@ -1368,7 +1364,7 @@ private function writePlotSeriesLabel(?DataSeriesValues $plotSeriesLabel, XMLWri
      * @param string $groupType Type of plot for dataseries
      * @param string $dataType Datatype of series values
      */
-    private function writePlotSeriesValues(?DataSeriesValues $plotSeriesValues, XMLWriter $objWriter, $groupType, $dataType = 'str'): void
+    private function writePlotSeriesValues(?DataSeriesValues $plotSeriesValues, XMLWriter $objWriter, string $groupType, string $dataType = 'str'): void
     {
         if ($plotSeriesValues === null) {
             return;
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Comments.php b/src/PhpSpreadsheet/Writer/Xlsx/Comments.php
index 91973884cb..f2b118b7c5 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Comments.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Comments.php
@@ -161,7 +161,7 @@ public function writeVMLComments(\PhpOffice\PhpSpreadsheet\Worksheet\Worksheet $
      * @param string $cellReference Cell reference, eg: 'A1'
      * @param Comment $comment Comment
      */
-    private function writeVMLComment(XMLWriter $objWriter, $cellReference, Comment $comment): void
+    private function writeVMLComment(XMLWriter $objWriter, string $cellReference, Comment $comment): void
     {
         // Metadata
         [$column, $row] = Coordinate::indexesFromString($cellReference);
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/ContentTypes.php b/src/PhpSpreadsheet/Writer/Xlsx/ContentTypes.php
index d399fa5b94..8faa3ffc2d 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/ContentTypes.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/ContentTypes.php
@@ -217,7 +217,7 @@ public function writeContentTypes(Spreadsheet $spreadsheet, $includeCharts = fal
      *
      * @return string Mime Type
      */
-    private function getImageMimeType($filename)
+    private function getImageMimeType($filename): string
     {
         if (File::fileExists($filename)) {
             $image = getimagesize($filename);
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/DefinedNames.php b/src/PhpSpreadsheet/Writer/Xlsx/DefinedNames.php
index f83280c5a3..54f5af4ad2 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/DefinedNames.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/DefinedNames.php
@@ -12,11 +12,9 @@
 
 class DefinedNames
 {
-    /** @var XMLWriter */
-    private $objWriter;
+    private XMLWriter $objWriter;
 
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
     public function __construct(XMLWriter $objWriter, Spreadsheet $spreadsheet)
     {
@@ -114,7 +112,7 @@ private function writeNamedRangeForAutofilter(ActualWorksheet $worksheet, int $w
             //    Strip any worksheet ref so we can make the cell ref absolute
             [, $range[0]] = ActualWorksheet::extractSheetTitle($range[0], true);
 
-            $range[0] = Coordinate::absoluteCoordinate($range[0]);
+            $range[0] = Coordinate::absoluteCoordinate($range[0] ?? '');
             if (count($range) > 1) {
                 $range[1] = Coordinate::absoluteCoordinate($range[1]);
             }
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php b/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php
index 5a5775882c..6763b508f2 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Drawing.php
@@ -501,7 +501,7 @@ public function writeVMLHeaderFooterImages(\PhpOffice\PhpSpreadsheet\Worksheet\W
      *
      * @param string $reference Reference
      */
-    private function writeVMLHeaderFooterImage(XMLWriter $objWriter, $reference, HeaderFooterDrawing $image): void
+    private function writeVMLHeaderFooterImage(XMLWriter $objWriter, string $reference, HeaderFooterDrawing $image): void
     {
         // Calculate object id
         preg_match('{(\d+)}', md5($reference), $m);
@@ -540,7 +540,7 @@ private function writeVMLHeaderFooterImage(XMLWriter $objWriter, $reference, Hea
      *
      * @return BaseDrawing[] All drawings in PhpSpreadsheet
      */
-    public function allDrawings(Spreadsheet $spreadsheet)
+    public function allDrawings(Spreadsheet $spreadsheet): array
     {
         // Get an array of all drawings
         $aDrawings = [];
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Rels.php b/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
index 70146a5002..1e288d3788 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Rels.php
@@ -459,7 +459,7 @@ public function writeVMLDrawingRelationships(\PhpOffice\PhpSpreadsheet\Worksheet
      * @param string $target Relationship target
      * @param string $targetMode Relationship target mode
      */
-    private function writeRelationship(XMLWriter $objWriter, $id, $type, $target, $targetMode = ''): void
+    private function writeRelationship(XMLWriter $objWriter, $id, string $type, $target, string $targetMode = ''): void
     {
         if ($type != '' && $target != '') {
             // Write relationship
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php b/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
index 29e95eb2fe..016c4a74df 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
@@ -21,7 +21,7 @@ class StringTable extends WriterPart
      *
      * @return string[] String table for worksheet
      */
-    public function createStringTable(ActualWorksheet $worksheet, $existingTable = null)
+    public function createStringTable(ActualWorksheet $worksheet, $existingTable = null): array
     {
         // Create string lookup table
         $aStringTable = [];
@@ -205,7 +205,7 @@ public function writeRichText(XMLWriter $objWriter, RichText $richText, $prefix
      * @param RichText|string $richText text string or Rich text
      * @param string $prefix Optional Namespace prefix
      */
-    public function writeRichTextForCharts(XMLWriter $objWriter, $richText = null, $prefix = ''): void
+    public function writeRichTextForCharts(XMLWriter $objWriter, $richText = null, string $prefix = ''): void
     {
         if (!($richText instanceof RichText)) {
             $textRun = $richText;
@@ -324,10 +324,8 @@ private function writeChartTextColor(XMLWriter $objWriter, ?ChartColor $underlin
      * Flip string table (for index searching).
      *
      * @param array $stringTable Stringtable
-     *
-     * @return array
      */
-    public function flipStringTable(array $stringTable)
+    public function flipStringTable(array $stringTable): array
     {
         // Return value
         $returnValue = [];
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Style.php b/src/PhpSpreadsheet/Writer/Xlsx/Style.php
index baafdc334d..fbded4d52f 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Style.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Style.php
@@ -567,7 +567,7 @@ private function writeCellStyleDxf(XMLWriter $objWriter, \PhpOffice\PhpSpreadshe
      *
      * @param string $name Element name
      */
-    private function writeBorderPr(XMLWriter $objWriter, $name, Border $border): void
+    private function writeBorderPr(XMLWriter $objWriter, string $name, Border $border): void
     {
         // Write BorderPr
         if ($border->getBorderStyle() === Border::BORDER_OMIT) {
@@ -592,7 +592,7 @@ private function writeBorderPr(XMLWriter $objWriter, $name, Border $border): voi
      *
      * @param int $id Number Format identifier
      */
-    private function writeNumFmt(XMLWriter $objWriter, ?NumberFormat $numberFormat, $id = 0): void
+    private function writeNumFmt(XMLWriter $objWriter, ?NumberFormat $numberFormat, int $id = 0): void
     {
         // Translate formatcode
         $formatCode = ($numberFormat === null) ? null : $numberFormat->getFormatCode();
@@ -621,7 +621,7 @@ public function allStyles(Spreadsheet $spreadsheet)
      *
      * @return Conditional[] All conditional styles in PhpSpreadsheet
      */
-    public function allConditionalStyles(Spreadsheet $spreadsheet)
+    public function allConditionalStyles(Spreadsheet $spreadsheet): array
     {
         // Get an array of all styles
         $aStyles = [];
@@ -673,7 +673,7 @@ public function allFills(Spreadsheet $spreadsheet)
      *
      * @return Font[] All fonts in PhpSpreadsheet
      */
-    public function allFonts(Spreadsheet $spreadsheet)
+    public function allFonts(Spreadsheet $spreadsheet): array
     {
         // Get an array of unique fonts
         $aFonts = [];
@@ -694,7 +694,7 @@ public function allFonts(Spreadsheet $spreadsheet)
      *
      * @return Borders[] All borders in PhpSpreadsheet
      */
-    public function allBorders(Spreadsheet $spreadsheet)
+    public function allBorders(Spreadsheet $spreadsheet): array
     {
         // Get an array of unique borders
         $aBorders = [];
@@ -715,7 +715,7 @@ public function allBorders(Spreadsheet $spreadsheet)
      *
      * @return NumberFormat[] All number formats in PhpSpreadsheet
      */
-    public function allNumberFormats(Spreadsheet $spreadsheet)
+    public function allNumberFormats(Spreadsheet $spreadsheet): array
     {
         // Get an array of unique number formats
         $aNumFmts = [];
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php b/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
index f2a8678219..971771f6e1 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
@@ -195,7 +195,7 @@ private function writeSheets(XMLWriter $objWriter, Spreadsheet $spreadsheet): vo
      * @param int $relId Relationship ID
      * @param string $sheetState Sheet state (visible, hidden, veryHidden)
      */
-    private function writeSheet(XMLWriter $objWriter, $worksheetName, $worksheetId = 1, $relId = 1, $sheetState = 'visible'): void
+    private function writeSheet(XMLWriter $objWriter, string $worksheetName, int $worksheetId = 1, $relId = 1, $sheetState = 'visible'): void
     {
         if ($worksheetName != '') {
             // Write sheet
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index 0e72c5d123..e36b853147 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -39,7 +39,7 @@ class Worksheet extends WriterPart
      *
      * @return string XML Output
      */
-    public function writeWorksheet(PhpspreadsheetWorksheet $worksheet, $stringTable = [], $includeCharts = false)
+    public function writeWorksheet(PhpspreadsheetWorksheet $worksheet, array $stringTable = [], $includeCharts = false)
     {
         $this->numberStoredAsText = '';
         $this->formula = '';
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php b/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php
index 0bfb356d83..9dbd904556 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/WriterPart.php
@@ -8,10 +8,8 @@ abstract class WriterPart
 {
     /**
      * Parent Xlsx object.
-     *
-     * @var Xlsx
      */
-    private $parentWriter;
+    private Xlsx $parentWriter;
 
     /**
      * Get parent Xlsx object.
diff --git a/tests/PhpSpreadsheetTests/A1LocaleGeneratorTest.php b/tests/PhpSpreadsheetTests/A1LocaleGeneratorTest.php
index 64da066391..243705c36b 100644
--- a/tests/PhpSpreadsheetTests/A1LocaleGeneratorTest.php
+++ b/tests/PhpSpreadsheetTests/A1LocaleGeneratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Calculation/ArrayFormulaTest.php b/tests/PhpSpreadsheetTests/Calculation/ArrayFormulaTest.php
index a089ec24e8..f1847fb645 100644
--- a/tests/PhpSpreadsheetTests/Calculation/ArrayFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/ArrayFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,10 +12,8 @@ class ArrayFormulaTest extends TestCase
 {
     /**
      * @dataProvider providerArrayFormulae
-     *
-     * @param mixed $expectedResult
      */
-    public function testArrayFormula(string $formula, $expectedResult): void
+    public function testArrayFormula(string $formula, mixed $expectedResult): void
     {
         $result = Calculation::getInstance()->_calculateFormulaValue($formula);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/ArrayTest.php b/tests/PhpSpreadsheetTests/Calculation/ArrayTest.php
index 60c336cf18..77b5251a7a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/ArrayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/ArrayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
diff --git a/tests/PhpSpreadsheetTests/Calculation/BinaryComparisonTest.php b/tests/PhpSpreadsheetTests/Calculation/BinaryComparisonTest.php
index 29f9090a57..86b8697563 100644
--- a/tests/PhpSpreadsheetTests/Calculation/BinaryComparisonTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/BinaryComparisonTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\BinaryComparison;
@@ -9,10 +11,7 @@
 
 class BinaryComparisonTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -27,13 +26,10 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerBinaryComparison
-     *
-     * @param mixed $operand1
-     * @param mixed $operand2
      */
     public function testBinaryComparisonOperation(
-        $operand1,
-        $operand2,
+        mixed $operand1,
+        mixed $operand2,
         string $operator,
         bool $expectedResultExcel,
         bool $expectedResultOpenOffice
diff --git a/tests/PhpSpreadsheetTests/Calculation/CalculationErrorTest.php b/tests/PhpSpreadsheetTests/Calculation/CalculationErrorTest.php
index 3ebc9888cc..9bbaca1a50 100644
--- a/tests/PhpSpreadsheetTests/Calculation/CalculationErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/CalculationErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Calculation/CalculationFunctionListTest.php b/tests/PhpSpreadsheetTests/Calculation/CalculationFunctionListTest.php
index 3d7e93a638..22c2c78b01 100644
--- a/tests/PhpSpreadsheetTests/Calculation/CalculationFunctionListTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/CalculationFunctionListTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -9,15 +11,9 @@
 
 class CalculationFunctionListTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
-    /**
-     * @var string
-     */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
@@ -36,12 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerGetFunctions
-     *
-     * @param string $category
-     * @param array|string $functionCall
-     * @param string $argumentCount
      */
-    public function testGetFunctions(/** @scrutinizer ignore-unused */ $category, $functionCall, /** @scrutinizer ignore-unused */ $argumentCount): void
+    public function testGetFunctions(/** @scrutinizer ignore-unused */ string $category, array|string $functionCall): void
     {
         self::assertIsCallable($functionCall);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/CalculationLoggingTest.php b/tests/PhpSpreadsheetTests/Calculation/CalculationLoggingTest.php
index cb11057471..b9243deb3d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/CalculationLoggingTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/CalculationLoggingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -72,7 +74,7 @@ public function testFormulaWithMultipleCellLogging(): void
         $finalEntry = array_pop($log);
         self::assertStringContainsString('Evaluation Result', $finalEntry);
 
-        $e1Log = array_filter($log, function ($entry) {
+        $e1Log = array_filter($log, function ($entry): bool {
             return strpos($entry, 'E1') !== false;
         });
         $e1Entries = count($e1Log);
@@ -81,7 +83,7 @@ public function testFormulaWithMultipleCellLogging(): void
         $e1FinalEntry = array_pop($e1Log);
         self::assertStringContainsString('Evaluation Result', $e1FinalEntry);
 
-        $e3Log = array_filter($log, function ($entry) {
+        $e3Log = array_filter($log, function ($entry): bool {
             return strpos($entry, 'E1') !== false;
         });
         $e3Entries = count($e3Log);
diff --git a/tests/PhpSpreadsheetTests/Calculation/CalculationSettingsTest.php b/tests/PhpSpreadsheetTests/Calculation/CalculationSettingsTest.php
index d72b6c06cd..afaf58d0ee 100644
--- a/tests/PhpSpreadsheetTests/Calculation/CalculationSettingsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/CalculationSettingsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,15 +10,9 @@
 
 class CalculationSettingsTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
-    /**
-     * @var string
-     */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
@@ -35,10 +31,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerCanLoadAllSupportedLocales
-     *
-     * @param string $locale
      */
-    public function testCanLoadAllSupportedLocales($locale): void
+    public function testCanLoadAllSupportedLocales(string $locale): void
     {
         $calculation = Calculation::getInstance();
         self::assertTrue($calculation->setLocale($locale));
diff --git a/tests/PhpSpreadsheetTests/Calculation/CalculationTest.php b/tests/PhpSpreadsheetTests/Calculation/CalculationTest.php
index 548e133e47..403ae86065 100644
--- a/tests/PhpSpreadsheetTests/Calculation/CalculationTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/CalculationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,15 +13,9 @@
 
 class CalculationTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
-    /**
-     * @var string
-     */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
@@ -38,12 +34,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerBinaryComparisonOperation
-     *
-     * @param mixed $formula
-     * @param mixed $expectedResultExcel
-     * @param mixed $expectedResultOpenOffice
      */
-    public function testBinaryComparisonOperation($formula, $expectedResultExcel, $expectedResultOpenOffice): void
+    public function testBinaryComparisonOperation(mixed $formula, mixed $expectedResultExcel, mixed $expectedResultOpenOffice): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_EXCEL);
         $resultExcel = Calculation::getInstance()->_calculateFormulaValue($formula);
@@ -358,9 +350,6 @@ public function testBranchPruningFormulaParsingInequalitiesConditionsCase(): voi
     }
 
     /**
-     * @param mixed $expectedResult
-     * @param mixed $dataArray
-     * @param string $formula
      * @param string $cellCoordinates where to put the formula
      * @param string[] $shouldBeSetInCacheCells coordinates of cells that must
      *  be set in cache
@@ -370,12 +359,12 @@ public function testBranchPruningFormulaParsingInequalitiesConditionsCase(): voi
      * @dataProvider dataProviderBranchPruningFullExecution
      */
     public function testFullExecutionDataPruning(
-        $expectedResult,
-        $dataArray,
-        $formula,
-        $cellCoordinates,
-        $shouldBeSetInCacheCells = [],
-        $shouldNotBeSetInCacheCells = []
+        mixed $expectedResult,
+        mixed $dataArray,
+        string $formula,
+        string $cellCoordinates,
+        array $shouldBeSetInCacheCells = [],
+        array $shouldNotBeSetInCacheCells = []
     ): void {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/CyclicTest.php b/tests/PhpSpreadsheetTests/Calculation/CyclicTest.php
index c754520bd0..2357c0bc92 100644
--- a/tests/PhpSpreadsheetTests/Calculation/CyclicTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/CyclicTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Calculation/DefinedNameConfusedForCellTest.php b/tests/PhpSpreadsheetTests/Calculation/DefinedNameConfusedForCellTest.php
index 6f97f9c87a..703996d9ac 100644
--- a/tests/PhpSpreadsheetTests/Calculation/DefinedNameConfusedForCellTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/DefinedNameConfusedForCellTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Calculation/DefinedNameWithQuotePrefixedCellTest.php b/tests/PhpSpreadsheetTests/Calculation/DefinedNameWithQuotePrefixedCellTest.php
index 0c2511640e..695850734b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/DefinedNameWithQuotePrefixedCellTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/DefinedNameWithQuotePrefixedCellTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
diff --git a/tests/PhpSpreadsheetTests/Calculation/DefinedNamesCalculationTest.php b/tests/PhpSpreadsheetTests/Calculation/DefinedNamesCalculationTest.php
index 4f450f57c5..d011f3c7f6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/DefinedNamesCalculationTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/DefinedNamesCalculationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberSlashTest.php b/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberSlashTest.php
index baaf32f276..9196bcc32a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberSlashTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberSlashTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Engine;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Engine\FormattedNumber;
@@ -30,10 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerNumbers
-     *
-     * @param mixed $expected
      */
-    public function testNumber($expected, string $value, string $thousandsSeparator = ',', string $decimalSeparator = '.'): void
+    public function testNumber(float $expected, string $value, string $thousandsSeparator = ',', string $decimalSeparator = '.'): void
     {
         StringHelper::setThousandsSeparator($thousandsSeparator);
         StringHelper::setDecimalSeparator($decimalSeparator);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberTest.php b/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberTest.php
index 72bbba9198..fef4d66b5b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Engine/FormattedNumberTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Engine;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Engine\FormattedNumber;
@@ -10,10 +12,8 @@ class FormattedNumberTest extends TestCase
 {
     /**
      * @dataProvider providerNumbers
-     *
-     * @param mixed $expected
      */
-    public function testNumber($expected, string $value): void
+    public function testNumber(float $expected, string $value): void
     {
         FormattedNumber::convertToNumberIfFormatted($value);
         self::assertSame($expected, $value);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Engine/RangeTest.php b/tests/PhpSpreadsheetTests/Calculation/Engine/RangeTest.php
index 229eec905a..c36c48d40e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Engine/RangeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Engine/RangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Engine;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
@@ -12,10 +14,7 @@ class RangeTest extends TestCase
     /** @var string */
     private $incompleteMessage = 'Must be revisited';
 
-    /**
-     * @var Spreadsheet
-     */
-    private $spreadSheet;
+    private \PhpOffice\PhpSpreadsheet\Spreadsheet $spreadSheet;
 
     protected function setUp(): void
     {
@@ -26,10 +25,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerRangeEvaluation
-     *
-     * @param mixed $expectedResult
      */
-    public function testRangeEvaluation(string $formula, $expectedResult): void
+    public function testRangeEvaluation(string $formula, int|string $expectedResult): void
     {
         $workSheet = $this->spreadSheet->getActiveSheet();
         $workSheet->setCellValue('H1', $formula);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceSlashTest.php b/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceSlashTest.php
index 8b652999b6..bd94002f9c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceSlashTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceSlashTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Engine;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Engine\Operands\StructuredReference;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceTest.php b/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceTest.php
index d78e7af63b..4597957013 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Engine/StructuredReferenceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Engine;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Engine\Operands\StructuredReference;
diff --git a/tests/PhpSpreadsheetTests/Calculation/FormulaAsStringTest.php b/tests/PhpSpreadsheetTests/Calculation/FormulaAsStringTest.php
index 40c453e758..aeb13e0b5b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/FormulaAsStringTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/FormulaAsStringTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -9,11 +11,8 @@ class FormulaAsStringTest extends TestCase
 {
     /**
      * @dataProvider providerFunctionsAsString
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testFunctionsAsString($expectedResult, $formula): void
+    public function testFunctionsAsString(mixed $expectedResult, string $formula): void
     {
         $spreadsheet = new Spreadsheet();
         $workSheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/FormulaParserTest.php b/tests/PhpSpreadsheetTests/Calculation/FormulaParserTest.php
index a913333d9c..10ce2cd488 100644
--- a/tests/PhpSpreadsheetTests/Calculation/FormulaParserTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/FormulaParserTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DAverageTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DAverageTest.php
index 777469525c..18978afa04 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DAverageTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DAverageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DAverage;
@@ -9,13 +11,8 @@ class DAverageTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDAverage
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDAverage($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDAverage(int|float|string $expectedResult, array $database, string|int|null $field, array $criteria): void
     {
         $result = DAverage::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,11 +20,8 @@ public function testDirectCallToDAverage($expectedResult, $database, $field, $cr
 
     /**
      * @dataProvider providerDAverage
-     *
-     * @param mixed $expectedResult
-     * @param int|string $field
      */
-    public function testDAverageAsWorksheetFormula($expectedResult, array $database, $field, array $criteria): void
+    public function testDAverageAsWorksheetFormula(int|float|string $expectedResult, array $database, string|int|null $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DAVERAGE', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountATest.php
index 0bbd0372af..6ddcfd6cbb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountATest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DCountA;
@@ -9,13 +11,8 @@ class DCountATest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDCountA
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDCountA($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDCountA(int|string $expectedResult, array $database, string $field, array $criteria): void
     {
         $result = DCountA::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDCountA($expectedResult, $database, $field, $cri
 
     /**
      * @dataProvider providerDCountA
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDCountAAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDCountAAsWorksheetFormula(int|string $expectedResult, array $database, string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DCOUNTA', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountTest.php
index a986e70048..ded350b937 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DCountTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DCount;
@@ -9,13 +11,8 @@ class DCountTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDCount
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDCount($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDCount(int|string $expectedResult, array $database, string|int|null $field, array $criteria): void
     {
         $result = DCount::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDCount($expectedResult, $database, $field, $crit
 
     /**
      * @dataProvider providerDCount
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDCountAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDCountAsWorksheetFormula(int|string $expectedResult, array $database, string|int|null $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DCOUNT', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DGetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DGetTest.php
index 24394c7d9a..0522616045 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DGetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DGetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DGet;
@@ -9,13 +11,8 @@ class DGetTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDGet
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDGet($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDGet(string|int $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DGet::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDGet($expectedResult, $database, $field, $criter
 
     /**
      * @dataProvider providerDGet
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDGetAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDGetAsWorksheetFormula(string|int $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DGET', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMaxTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMaxTest.php
index a4dc9f9e74..2689fa3cf3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMaxTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMaxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DMax;
@@ -9,13 +11,8 @@ class DMaxTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDMax
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDMax($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDMax(int|string $expectedResult, array $database, string|null|int $field, array $criteria): void
     {
         $result = DMax::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDMax($expectedResult, $database, $field, $criter
 
     /**
      * @dataProvider providerDMax
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDMaxAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDMaxAsWorksheetFormula(int|string $expectedResult, array $database, string|null|int $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DMAX', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMinTest.php
index c3257d2722..c1e553dc18 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DMinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DMin;
@@ -9,13 +11,8 @@ class DMinTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDMin
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDMin($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDMin(int|float|string $expectedResult, array $database, string|null|int $field, array $criteria): void
     {
         $result = DMin::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDMin($expectedResult, $database, $field, $criter
 
     /**
      * @dataProvider providerDMin
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDMinAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDMinAsWorksheetFormula(int|float|string $expectedResult, array $database, string|null|int $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DMIN', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DProductTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DProductTest.php
index 6aca35b62c..57590ee253 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DProductTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DProductTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DProduct;
@@ -10,13 +12,8 @@ class DProductTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDProduct
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDProduct($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDProduct(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DProduct::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -24,13 +21,8 @@ public function testDirectCallToDProduct($expectedResult, $database, $field, $cr
 
     /**
      * @dataProvider providerDProduct
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDProductAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDProductAsWorksheetFormula(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DPRODUCT', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevPTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevPTest.php
index 1c73535732..bb80b211bb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevPTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevPTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DStDevP;
@@ -9,13 +11,8 @@ class DStDevPTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDStDevP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDStDevP($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDStDevP(float|int|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DStDevP::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDStDevP($expectedResult, $database, $field, $cri
 
     /**
      * @dataProvider providerDStDevP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDStDevPAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDStDevPAsWorksheetFormula(float|int|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DSTDEVP', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevTest.php
index 7698e73ec4..73eb7a4108 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DStDevTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DStDev;
@@ -9,13 +11,8 @@ class DStDevTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDStDev
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDStDev($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDStDev(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DStDev::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDStDev($expectedResult, $database, $field, $crit
 
     /**
      * @dataProvider providerDStDev
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDStDevAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDStDevAsWorksheetFormula(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DSTDEV', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DSumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DSumTest.php
index 6f16c3e658..3589e89595 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DSumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DSumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DSum;
@@ -9,13 +11,8 @@ class DSumTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDSum
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDSum($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDSum(int|float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DSum::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDSum($expectedResult, $database, $field, $criter
 
     /**
      * @dataProvider providerDSum
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDSumAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDSumAsWorksheetFormula(int|float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DSUM', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarPTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarPTest.php
index 3e12fd0a6a..c880bb62e7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarPTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarPTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DVarP;
@@ -9,13 +11,8 @@ class DVarPTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDVarP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDVarP($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDVarP(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DVarP::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDVarP($expectedResult, $database, $field, $crite
 
     /**
      * @dataProvider providerDVarP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDVarPAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDVarPAsWorksheetFormula(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DVARP', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarTest.php
index da8c31c3d8..7a0e923f99 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/DVarTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Database\DVar;
@@ -9,13 +11,8 @@ class DVarTest extends SetupTeardownDatabases
 {
     /**
      * @dataProvider providerDVar
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDirectCallToDVar($expectedResult, $database, $field, $criteria): void
+    public function testDirectCallToDVar(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $result = DVar::evaluate($database, $field, $criteria);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -23,13 +20,8 @@ public function testDirectCallToDVar($expectedResult, $database, $field, $criter
 
     /**
      * @dataProvider providerDVar
-     *
-     * @param mixed $expectedResult
-     * @param mixed $database
-     * @param mixed $field
-     * @param mixed $criteria
      */
-    public function testDVarAsWorksheetFormula($expectedResult, $database, $field, $criteria): void
+    public function testDVarAsWorksheetFormula(float|string $expectedResult, array $database, ?string $field, array $criteria): void
     {
         $this->prepareWorksheetWithFormula('DVAR', $database, $field, $criteria);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/SetupTeardownDatabases.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/SetupTeardownDatabases.php
index 9c79d9ae13..c280b6725b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Database/SetupTeardownDatabases.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Database/SetupTeardownDatabases.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Database;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -132,10 +134,7 @@ protected function getSheet(): Worksheet
         return $this->sheet;
     }
 
-    /**
-     * @param int|string $field
-     */
-    public function prepareWorksheetWithFormula(string $functionName, array $database, $field, array $criteria): void
+    public function prepareWorksheetWithFormula(string $functionName, array $database, null|int|string $field, array $criteria): void
     {
         $sheet = $this->getSheet();
         $maxCol = '';
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateDifTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateDifTest.php
index d4218c4e91..260a563cf1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateDifTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateDifTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTime;
@@ -18,10 +20,8 @@ class DateDifTest extends TestCase
 {
     /**
      * @dataProvider providerDATEDIF
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDATEDIF($expectedResult, string ...$args): void
+    public function testDirectCallToDATEDIF(array|int|string $expectedResult, string ...$args): void
     {
         $result = Difference::interval(...$args);
         self::assertSame($expectedResult, $result);
@@ -29,10 +29,8 @@ public function testDirectCallToDATEDIF($expectedResult, string ...$args): void
 
     /**
      * @dataProvider providerDATEDIF
-     *
-     * @param mixed $expectedResult
      */
-    public function testDATEDIFAsFormula($expectedResult, ...$args): void
+    public function testDATEDIFAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -45,10 +43,8 @@ public function testDATEDIFAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDATEDIF
-     *
-     * @param mixed $expectedResult
      */
-    public function testDATEDIFInWorksheet($expectedResult, ...$args): void
+    public function testDATEDIFInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -73,7 +69,7 @@ public static function providerDATEDIF(): array
     /**
      * @dataProvider providerUnhappyDATEDIF
      */
-    public function testDATEDIFUnhappyPath(string $expectedException, ...$args): void
+    public function testDATEDIFUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -109,6 +105,7 @@ public function testNonDateObject(): void
     {
         $obj1 = new Exception();
         $obj2 = new DateTimeImmutable('2000-2-29');
+        // @phpstan-ignore-next-line
         self::assertSame(ExcelError::VALUE(), Days::between($obj1, $obj2));
     }
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php
index 0386056e80..494b41b905 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -14,15 +16,9 @@
 
 class DateTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
-    /**
-     * @var string
-     */
-    private $returnDateType;
+    private string $returnDateType;
 
     protected function setUp(): void
     {
@@ -42,10 +38,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerDATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDATE($expectedResult, ...$args): void
+    public function testDirectCallToDATE(mixed $expectedResult, mixed ...$args): void
     {
         $result = Date::fromYMD(...$args);
         self::assertSame($expectedResult, $result);
@@ -53,10 +47,8 @@ public function testDirectCallToDATE($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDATEAsFormula($expectedResult, ...$args): void
+    public function testDATEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -69,10 +61,8 @@ public function testDATEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDATEInWorksheet($expectedResult, ...$args): void
+    public function testDATEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -97,7 +87,7 @@ public static function providerDATE(): array
     /**
      * @dataProvider providerUnhappyDATE
      */
-    public function testDATEUnhappyPath(string $expectedException, ...$args): void
+    public function testDATEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php
index 9c5abb4105..be35cb29eb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DateValueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTimeImmutable;
@@ -15,15 +17,9 @@
 
 class DateValueTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
-    /**
-     * @var string
-     */
-    private $returnDateType;
+    private string $returnDateType;
 
     protected function setUp(): void
     {
@@ -41,7 +37,7 @@ protected function tearDown(): void
         Functions::setReturnDateType($this->returnDateType);
     }
 
-    private function expectationIsTemplate(string $expectedResult): bool
+    private function expectationIsTemplate(mixed $expectedResult): bool
     {
         return is_string($expectedResult) && substr($expectedResult, 0, 2) === 'Y-';
     }
@@ -57,10 +53,8 @@ private function parseTemplatedExpectation(string $expectedResult): string
 
     /**
      * @dataProvider providerDATEVALUE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDATEVALUE($expectedResult, ...$args): void
+    public function testDirectCallToDATEVALUE(mixed $expectedResult, mixed ...$args): void
     {
         if ($this->expectationIsTemplate($expectedResult)) {
             $expectedResult = $this->parseTemplatedExpectation($expectedResult);
@@ -73,10 +67,8 @@ public function testDirectCallToDATEVALUE($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDATEVALUE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDATEVALUEAsFormula($expectedResult, ...$args): void
+    public function testDATEVALUEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         if ($this->expectationIsTemplate($expectedResult)) {
             $expectedResult = $this->parseTemplatedExpectation($expectedResult);
@@ -93,10 +85,8 @@ public function testDATEVALUEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDATEVALUE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDATEVALUEInWorksheet($expectedResult, ...$args): void
+    public function testDATEVALUEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         if ($this->expectationIsTemplate($expectedResult)) {
             $expectedResult = $this->parseTemplatedExpectation($expectedResult);
@@ -134,7 +124,7 @@ public function testRefArgNull(): void
     /**
      * @dataProvider providerUnhappyDATEVALUE
      */
-    public function testDATEVALUEUnhappyPath(string $expectedException, ...$args): void
+    public function testDATEVALUEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DayTest.php
index feeab4672f..6270ac0888 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class DayTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -33,10 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerDAY
-     *
-     * @param mixed $expectedResultExcel
      */
-    public function testDirectCallToDAY($expectedResultExcel, ...$args): void
+    public function testDirectCallToDAY(mixed $expectedResultExcel, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = DateParts::day(...$args);
@@ -45,10 +42,8 @@ public function testDirectCallToDAY($expectedResultExcel, ...$args): void
 
     /**
      * @dataProvider providerDAY
-     *
-     * @param mixed $expectedResultExcel
      */
-    public function testDAYAsFormula($expectedResultExcel, ...$args): void
+    public function testDAYAsFormula(mixed $expectedResultExcel, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -61,10 +56,8 @@ public function testDAYAsFormula($expectedResultExcel, ...$args): void
 
     /**
      * @dataProvider providerDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testDAYInWorksheet($expectedResult, ...$args): void
+    public function testDAYInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -88,10 +81,8 @@ public static function providerDAY(): array
 
     /**
      * @dataProvider providerDAYOpenOffice
-     *
-     * @param mixed $expectedResultOpenOffice
      */
-    public function testDirectCallToDAYOpenOffice($expectedResultOpenOffice, ...$args): void
+    public function testDirectCallToDAYOpenOffice(mixed $expectedResultOpenOffice, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
@@ -102,10 +93,8 @@ public function testDirectCallToDAYOpenOffice($expectedResultOpenOffice, ...$arg
 
     /**
      * @dataProvider providerDAYOpenOffice
-     *
-     * @param mixed $expectedResultOpenOffice
      */
-    public function testDAYAsFormulaOpenOffice($expectedResultOpenOffice, ...$args): void
+    public function testDAYAsFormulaOpenOffice(mixed $expectedResultOpenOffice, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
@@ -126,7 +115,7 @@ public static function providerDAYOpenOffice(): array
     /**
      * @dataProvider providerUnhappyDAY
      */
-    public function testDAYUnhappyPath(string $expectedException, ...$args): void
+    public function testDAYUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/Days360Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/Days360Test.php
index 084209eb1c..3e78810579 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/Days360Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/Days360Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTime;
@@ -18,10 +20,8 @@ class Days360Test extends TestCase
 {
     /**
      * @dataProvider providerDAYS360
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDAYS360($expectedResult, ...$args): void
+    public function testDirectCallToDAYS360(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Days360::between(...$args);
@@ -30,10 +30,8 @@ public function testDirectCallToDAYS360($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDAYS360
-     *
-     * @param mixed $expectedResult
      */
-    public function testDAYS360AsFormula($expectedResult, ...$args): void
+    public function testDAYS360AsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -46,10 +44,8 @@ public function testDAYS360AsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDAYS360
-     *
-     * @param mixed $expectedResult
      */
-    public function testDAYS360InWorksheet($expectedResult, ...$args): void
+    public function testDAYS360InWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -74,7 +70,7 @@ public static function providerDAYS360(): array
     /**
      * @dataProvider providerUnhappyDAYS360
      */
-    public function testDAYS360UnhappyPath(string $expectedException, ...$args): void
+    public function testDAYS360UnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -110,6 +106,7 @@ public function testNonDateObject(): void
     {
         $obj1 = new Exception();
         $obj2 = new DateTimeImmutable('2000-2-29');
+        // @phpstan-ignore-next-line
         self::assertSame(ExcelError::VALUE(), Days::between($obj1, $obj2));
     }
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DaysTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DaysTest.php
index 783bec8e77..15e023d325 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DaysTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/DaysTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTime;
@@ -17,10 +19,8 @@ class DaysTest extends TestCase
 {
     /**
      * @dataProvider providerDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDAYS($expectedResult, ...$args): void
+    public function testDirectCallToDAYS(mixed $expectedResult, mixed ...$args): void
     {
         $result = Days::between(...$args);
         self::assertSame($expectedResult, $result);
@@ -28,10 +28,8 @@ public function testDirectCallToDAYS($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testDAYSAsFormula($expectedResult, ...$args): void
+    public function testDAYSAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -44,10 +42,8 @@ public function testDAYSAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testDAYSInWorksheet($expectedResult, ...$args): void
+    public function testDAYSInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -72,7 +68,7 @@ public static function providerDAYS(): array
     /**
      * @dataProvider providerUnhappyDAYS
      */
-    public function testDAYSUnhappyPath(string $expectedException, ...$args): void
+    public function testDAYSUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -108,6 +104,7 @@ public function testNonDateObject(): void
     {
         $obj1 = new Exception();
         $obj2 = new DateTimeImmutable('2000-2-29');
+        // @phpstan-ignore-next-line
         self::assertSame(ExcelError::VALUE(), Days::between($obj1, $obj2));
     }
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EDateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EDateTest.php
index 7f1a0fdac7..a1618cf0d0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EDateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EDateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class EDateTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $returnDateType;
+    private string $returnDateType;
 
     protected function setUp(): void
     {
@@ -33,10 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerEDATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToEDATE($expectedResult, ...$args): void
+    public function testDirectCallToEDATE(mixed $expectedResult, mixed ...$args): void
     {
         $result = Month::adjust(...$args);
         self::assertSame($expectedResult, $result);
@@ -44,10 +41,8 @@ public function testDirectCallToEDATE($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerEDATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testEDATEAsFormula($expectedResult, ...$args): void
+    public function testEDATEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -60,10 +55,8 @@ public function testEDATEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerEDATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testEDATEInWorksheet($expectedResult, ...$args): void
+    public function testEDATEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -88,7 +81,7 @@ public static function providerEDATE(): array
     /**
      * @dataProvider providerUnhappyEDATE
      */
-    public function testEDATEUnhappyPath(string $expectedException, ...$args): void
+    public function testEDATEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EoMonthTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EoMonthTest.php
index 0f09e684e2..a6d5738960 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EoMonthTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/EoMonthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class EoMonthTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $returnDateType;
+    private string $returnDateType;
 
     protected function setUp(): void
     {
@@ -33,10 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerEOMONTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToEOMONTH($expectedResult, ...$args): void
+    public function testDirectCallToEOMONTH(mixed $expectedResult, mixed ...$args): void
     {
         $result = Month::lastDay(...$args);
         self::assertSame($expectedResult, $result);
@@ -44,10 +41,8 @@ public function testDirectCallToEOMONTH($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerEOMONTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testEOMONTHAsFormula($expectedResult, ...$args): void
+    public function testEOMONTHAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -60,10 +55,8 @@ public function testEOMONTHAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerEOMONTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testEOMONTHInWorksheet($expectedResult, ...$args): void
+    public function testEOMONTHInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -88,7 +81,7 @@ public static function providerEOMONTH(): array
     /**
      * @dataProvider providerUnhappyEOMONTH
      */
-    public function testEOMONTHUnhappyPath(string $expectedException, ...$args): void
+    public function testEOMONTHUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/HourTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/HourTest.php
index 5e0b1478b6..68781ffd03 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/HourTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/HourTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class HourTest extends TestCase
 {
     /**
      * @dataProvider providerHOUR
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToHOUR($expectedResult, ...$args): void
+    public function testDirectCallToHOUR(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = TimeParts::hour(...$args);
@@ -25,10 +25,8 @@ public function testDirectCallToHOUR($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerHOUR
-     *
-     * @param mixed $expectedResult
      */
-    public function testHOURAsFormula($expectedResult, ...$args): void
+    public function testHOURAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -41,10 +39,8 @@ public function testHOURAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerHOUR
-     *
-     * @param mixed $expectedResult
      */
-    public function testHOURInWorksheet($expectedResult, ...$args): void
+    public function testHOURInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -69,7 +65,7 @@ public static function providerHOUR(): array
     /**
      * @dataProvider providerUnhappyHOUR
      */
-    public function testHOURUnhappyPath(string $expectedException, ...$args): void
+    public function testHOURUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php
index 867096efd2..7aee56b9ac 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class IsoWeekNumTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
     protected function setUp(): void
     {
@@ -33,11 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerISOWEEKNUM
-     *
-     * @param mixed $expectedResult
-     * @param mixed ...$args
      */
-    public function testDirectCallToISOWEEKNUM($expectedResult, ...$args): void
+    public function testDirectCallToISOWEEKNUM(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Week::isoWeekNumber(...$args);
@@ -46,11 +42,8 @@ public function testDirectCallToISOWEEKNUM($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerISOWEEKNUM
-     *
-     * @param mixed $expectedResult
-     * @param mixed ...$args
      */
-    public function testISOWEEKNUMAsFormula($expectedResult, ...$args): void
+    public function testISOWEEKNUMAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +56,8 @@ public function testISOWEEKNUMAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerISOWEEKNUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testISOWEEKNUMInWorksheet($expectedResult, ...$args): void
+    public function testISOWEEKNUMInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +82,7 @@ public static function providerISOWEEKNUM(): array
     /**
      * @dataProvider providerUnhappyISOWEEKNUM
      */
-    public function testISOWEEKNUMUnhappyPath(string $expectedException, ...$args): void
+    public function testISOWEEKNUMUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +109,8 @@ public static function providerUnhappyISOWEEKNUM(): array
 
     /**
      * @dataProvider providerISOWEEKNUM1904
-     *
-     * @param mixed $expectedResult
      */
-    public function testISOWEEKNUMWith1904Calendar($expectedResult, ...$args): void
+    public function testISOWEEKNUMWith1904Calendar(mixed $expectedResult, mixed ...$args): void
     {
         SharedDate::setExcelCalendar(SharedDate::CALENDAR_MAC_1904);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MinuteTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MinuteTest.php
index f3db660430..3c987452bf 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MinuteTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MinuteTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class MinuteTest extends TestCase
 {
     /**
      * @dataProvider providerMINUTE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToMINUTE($expectedResult, ...$args): void
+    public function testDirectCallToMINUTE(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = TimeParts::MINUTE(...$args);
@@ -25,10 +25,8 @@ public function testDirectCallToMINUTE($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerMINUTE
-     *
-     * @param mixed $expectedResult
      */
-    public function testMINUTEAsFormula($expectedResult, ...$args): void
+    public function testMINUTEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -41,10 +39,8 @@ public function testMINUTEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerMINUTE
-     *
-     * @param mixed $expectedResult
      */
-    public function testMINUTEInWorksheet($expectedResult, ...$args): void
+    public function testMINUTEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -69,7 +65,7 @@ public static function providerMINUTE(): array
     /**
      * @dataProvider providerUnhappyMINUTE
      */
-    public function testMINUTEUnhappyPath(string $expectedException, ...$args): void
+    public function testMINUTEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MonthTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MonthTest.php
index 0b3cabee70..fdb91fff2d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MonthTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MonthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class MonthTest extends TestCase
 {
     /**
      * @dataProvider providerMONTH
-     *
-     * @param mixed $expectedResultExcel
      */
-    public function testDirectCallToMONTH($expectedResultExcel, ...$args): void
+    public function testDirectCallToMONTH(mixed $expectedResultExcel, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = DateParts::month(...$args);
@@ -25,10 +25,8 @@ public function testDirectCallToMONTH($expectedResultExcel, ...$args): void
 
     /**
      * @dataProvider providerMONTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testMONTHAsFormula($expectedResult, ...$args): void
+    public function testMONTHAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -41,10 +39,8 @@ public function testMONTHAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerMONTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testMONTHInWorksheet($expectedResult, ...$args): void
+    public function testMONTHInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -69,7 +65,7 @@ public static function providerMONTH(): array
     /**
      * @dataProvider providerUnhappyMONTH
      */
-    public function testMONTHUnhappyPath(string $expectedException, ...$args): void
+    public function testMONTHUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MovedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MovedFunctionsTest.php
index 0d640a4830..9aba4adef6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MovedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/MovedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NetworkDaysTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NetworkDaysTest.php
index b088014d98..0e853040af 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NetworkDaysTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NetworkDaysTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,8 @@ class NetworkDaysTest extends TestCase
 {
     /**
      * @dataProvider providerNETWORKDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToNETWORKDAYS($expectedResult, ...$args): void
+    public function testDirectCallToNETWORKDAYS(mixed $expectedResult, mixed ...$args): void
     {
         $result = NetworkDays::count(...$args);
         self::assertSame($expectedResult, $result);
@@ -23,10 +23,8 @@ public function testDirectCallToNETWORKDAYS($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerNETWORKDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testNETWORKDAYSAsFormula($expectedResult, ...$args): void
+    public function testNETWORKDAYSAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -39,10 +37,8 @@ public function testNETWORKDAYSAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerNETWORKDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testNETWORKDAYSInWorksheet($expectedResult, ...$args): void
+    public function testNETWORKDAYSInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,7 +63,7 @@ public static function providerNETWORKDAYS(): array
     /**
      * @dataProvider providerUnhappyNETWORKDAYS
      */
-    public function testNETWORKDAYSUnhappyPath(string $expectedException, ...$args): void
+    public function testNETWORKDAYSUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php
index e9fdd72931..c69239157c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/NowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTimeImmutable;
@@ -11,10 +13,7 @@
 
 class NowTest extends TestCase
 {
-    /**
-     * @param mixed $result
-     */
-    private function assertions(DateTimeImmutable $dtStart, $result): void
+    private function assertions(DateTimeImmutable $dtStart, mixed $result): void
     {
         self::assertEquals($dtStart->format('Y'), DateParts::year($result));
         self::assertEquals($dtStart->format('m'), DateParts::month($result));
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/SecondTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/SecondTest.php
index b74af2c481..f440ecaef7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/SecondTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/SecondTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,8 @@ class SecondTest extends TestCase
 {
     /**
      * @dataProvider providerSECOND
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToSECOND($expectedResult, ...$args): void
+    public function testDirectCallToSECOND(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = TimeParts::second(...$args);
@@ -24,10 +24,8 @@ public function testDirectCallToSECOND($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerSECOND
-     *
-     * @param mixed $expectedResult
      */
-    public function testSECONDAsFormula($expectedResult, ...$args): void
+    public function testSECONDAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testSECONDAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerSECOND
-     *
-     * @param mixed $expectedResult
      */
-    public function testSECONDInWorksheet($expectedResult, ...$args): void
+    public function testSECONDInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerSECOND(): array
     /**
      * @dataProvider providerUnhappySECOND
      */
-    public function testSECONDUnhappyPath(string $expectedException, ...$args): void
+    public function testSECONDUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php
index ea3c6b8025..f1097ba1b4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -14,15 +16,9 @@
 
 class TimeTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
-    /**
-     * @var string
-     */
-    private $returnDateType;
+    private string $returnDateType;
 
     protected function setUp(): void
     {
@@ -42,10 +38,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerTIME
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToTIME($expectedResult, ...$args): void
+    public function testDirectCallToTIME(mixed $expectedResult, mixed ...$args): void
     {
         $result = Time::fromHMS(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
@@ -53,10 +47,8 @@ public function testDirectCallToTIME($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerTIME
-     *
-     * @param mixed $expectedResult
      */
-    public function testTIMEAsFormula($expectedResult, ...$args): void
+    public function testTIMEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -75,7 +67,7 @@ public static function providerTIME(): array
     /**
      * @dataProvider providerUnhappyTIME
      */
-    public function testTIMEUnhappyPath(string $expectedException, ...$args): void
+    public function testTIMEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeValueTest.php
index b3f5ee5cf5..f188c1408c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeValueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TimeValueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class TimeValueTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $returnDateType;
+    private string $returnDateType;
 
     protected function setUp(): void
     {
@@ -33,10 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerTIMEVALUE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToTIMEVALUE($expectedResult, ...$args): void
+    public function testDirectCallToTIMEVALUE(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = TimeValue::fromString(...$args);
@@ -45,10 +42,8 @@ public function testDirectCallToTIMEVALUE($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerTIMEVALUE
-     *
-     * @param mixed $expectedResult
      */
-    public function testTIMEVALUEAsFormula($expectedResult, ...$args): void
+    public function testTIMEVALUEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -61,10 +56,8 @@ public function testTIMEVALUEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerTIMEVALUE
-     *
-     * @param mixed $expectedResult
      */
-    public function testTIMEVALUEInWorksheet($expectedResult, ...$args): void
+    public function testTIMEVALUEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -120,7 +113,7 @@ public function testTIMEVALUEtoDateTimeObject(): void
     /**
      * @dataProvider providerUnhappyTIMEVALUE
      */
-    public function testTIMEVALUEUnhappyPath(string $expectedException, ...$args): void
+    public function testTIMEVALUEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TodayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TodayTest.php
index fb9f4f5981..006ac6bb94 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TodayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/TodayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use DateTimeImmutable;
@@ -11,10 +13,7 @@
 
 class TodayTest extends TestCase
 {
-    /**
-     * @param mixed $result
-     */
-    private function assertions(DateTimeImmutable $dtStart, $result): void
+    private function assertions(DateTimeImmutable $dtStart, mixed $result): void
     {
         self::assertEquals($dtStart->format('Y'), DateParts::year($result));
         self::assertEquals($dtStart->format('m'), DateParts::month($result));
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
index 90974215a0..cf487bfd0e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekDayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,10 +13,7 @@
 
 class WeekDayTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
     protected function setUp(): void
     {
@@ -32,10 +31,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerWEEKDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToWEEKDAY($expectedResult, ...$args): void
+    public function testDirectCallToWEEKDAY(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Week::day(...$args);
@@ -44,10 +41,8 @@ public function testDirectCallToWEEKDAY($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerWEEKDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testWEEKDAYAsFormula($expectedResult, ...$args): void
+    public function testWEEKDAYAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -60,10 +55,8 @@ public function testWEEKDAYAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerWEEKDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testWEEKDAYInWorksheet($expectedResult, ...$args): void
+    public function testWEEKDAYInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -88,7 +81,7 @@ public static function providerWEEKDAY(): array
     /**
      * @dataProvider providerUnhappyWEEKDAY
      */
-    public function testWEEKDAYUnhappyPath(string $expectedException, ...$args): void
+    public function testWEEKDAYUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
index 35b8116e54..555418aded 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class WeekNumTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
     protected function setUp(): void
     {
@@ -33,10 +32,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerWEEKNUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToWEEKNUM($expectedResult, ...$args): void
+    public function testDirectCallToWEEKNUM(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Week::number(...$args);
@@ -45,10 +42,8 @@ public function testDirectCallToWEEKNUM($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerWEEKNUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testWEEKNUMAsFormula($expectedResult, ...$args): void
+    public function testWEEKNUMAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -61,10 +56,8 @@ public function testWEEKNUMAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerWEEKNUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testWEEKNUMInWorksheet($expectedResult, ...$args): void
+    public function testWEEKNUMInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -89,7 +82,7 @@ public static function providerWEEKNUM(): array
     /**
      * @dataProvider providerUnhappyWEEKNUM
      */
-    public function testWEEKNUMUnhappyPath(string $expectedException, ...$args): void
+    public function testWEEKNUMUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -116,10 +109,8 @@ public static function providerUnhappyWEEKNUM(): array
 
     /**
      * @dataProvider providerWEEKNUM1904
-     *
-     * @param mixed $expectedResult
      */
-    public function testWEEKNUMWith1904Calendar($expectedResult, ...$args): void
+    public function testWEEKNUMWith1904Calendar(mixed $expectedResult, mixed ...$args): void
     {
         SharedDate::setExcelCalendar(SharedDate::CALENDAR_MAC_1904);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WorkDayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WorkDayTest.php
index 031dff235b..db9d95d172 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WorkDayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WorkDayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,8 @@ class WorkDayTest extends TestCase
 {
     /**
      * @dataProvider providerWORKDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToWORKDAY($expectedResult, ...$args): void
+    public function testDirectCallToWORKDAY(mixed $expectedResult, mixed ...$args): void
     {
         $result = WorkDay::date(...$args);
         self::assertSame($expectedResult, $result);
@@ -23,10 +23,8 @@ public function testDirectCallToWORKDAY($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerWORKDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testWORKDAYAsFormula($expectedResult, ...$args): void
+    public function testWORKDAYAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -39,10 +37,8 @@ public function testWORKDAYAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerWORKDAY
-     *
-     * @param mixed $expectedResult
      */
-    public function testWORKDAYInWorksheet($expectedResult, ...$args): void
+    public function testWORKDAYInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,7 +63,7 @@ public static function providerWORKDAY(): array
     /**
      * @dataProvider providerUnhappyWORKDAY
      */
-    public function testWORKDAYUnhappyPath(string $expectedException, ...$args): void
+    public function testWORKDAYUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearFracTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearFracTest.php
index 53b6341afb..74157492a2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearFracTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearFracTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class YearFracTest extends TestCase
 {
     /**
      * @dataProvider providerYEARFRAC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToYEARFRAC($expectedResult, ...$args): void
+    public function testDirectCallToYEARFRAC(mixed $expectedResult, mixed ...$args): void
     {
         $result = YearFrac::fraction(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-6);
@@ -24,10 +24,8 @@ public function testDirectCallToYEARFRAC($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerYEARFRAC
-     *
-     * @param mixed $expectedResult
      */
-    public function testYEARFRACAsFormula($expectedResult, ...$args): void
+    public function testYEARFRACAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testYEARFRACAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerYEARFRAC
-     *
-     * @param mixed $expectedResult
      */
-    public function testYEARFRACInWorksheet($expectedResult, ...$args): void
+    public function testYEARFRACInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerYEARFRAC(): array
     /**
      * @dataProvider providerUnhappyYEARFRAC
      */
-    public function testYEARFRACUnhappyPath(string $expectedException, ...$args): void
+    public function testYEARFRACUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearTest.php
index 192878c677..e913a56191 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/YearTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\DateTime;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,8 @@ class YearTest extends TestCase
 {
     /**
      * @dataProvider providerYEAR
-     *
-     * @param mixed $expectedResultExcel
      */
-    public function testDirectCallToYEAR($expectedResultExcel, ...$args): void
+    public function testDirectCallToYEAR(mixed $expectedResultExcel, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = DateParts::year(...$args);
@@ -24,10 +24,8 @@ public function testDirectCallToYEAR($expectedResultExcel, ...$args): void
 
     /**
      * @dataProvider providerYEAR
-     *
-     * @param mixed $expectedResult
      */
-    public function testYEARAsFormula($expectedResult, ...$args): void
+    public function testYEARAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testYEARAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerYEAR
-     *
-     * @param mixed $expectedResult
      */
-    public function testYEARInWorksheet($expectedResult, ...$args): void
+    public function testYEARInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerYEAR(): array
     /**
      * @dataProvider providerUnhappyYEAR
      */
-    public function testYEARUnhappyPath(string $expectedException, ...$args): void
+    public function testYEARUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DeprecatedExcelErrorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DeprecatedExcelErrorTest.php
index 26e8ad77ad..a2356f7fad 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DeprecatedExcelErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DeprecatedExcelErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -10,10 +12,8 @@ class DeprecatedExcelErrorTest extends TestCase
 {
     /**
      * @dataProvider providerDeprecatedExcelError
-     *
-     * @param mixed $expectedResult
      */
-    public function testDeprecatedExcelError(callable $deprecatedMethod, $expectedResult): void
+    public function testDeprecatedExcelError(callable $deprecatedMethod, mixed $expectedResult): void
     {
         $result = $deprecatedMethod();
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselITest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselITest.php
index a80954a367..8a659358c8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselITest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselITest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class BesselITest extends TestCase
 
     /**
      * @dataProvider providerBESSELI
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBESSELI($expectedResult, ...$args): void
+    public function testDirectCallToBESSELI(mixed $expectedResult, mixed ...$args): void
     {
         $result = BesselI::besselI(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, self::BESSEL_PRECISION);
@@ -26,10 +26,8 @@ public function testDirectCallToBESSELI($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELI
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELIAsFormula($expectedResult, ...$args): void
+    public function testBESSELIAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -42,10 +40,8 @@ public function testBESSELIAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELI
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELIInWorksheet($expectedResult, ...$args): void
+    public function testBESSELIInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -70,7 +66,7 @@ public static function providerBESSELI(): array
     /**
      * @dataProvider providerUnhappyBESSELI
      */
-    public function testBESSELIUnhappyPath(string $expectedException, ...$args): void
+    public function testBESSELIUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselJTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselJTest.php
index 1698c8ad76..ce8930505b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselJTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselJTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class BesselJTest extends TestCase
 
     /**
      * @dataProvider providerBESSELJ
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBESSELJ($expectedResult, ...$args): void
+    public function testDirectCallToBESSELJ(mixed $expectedResult, mixed ...$args): void
     {
         $result = BesselJ::besselJ(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, self::BESSEL_PRECISION);
@@ -26,10 +26,8 @@ public function testDirectCallToBESSELJ($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELJ
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELJAsFormula($expectedResult, ...$args): void
+    public function testBESSELJAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -42,10 +40,8 @@ public function testBESSELJAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELJ
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELJInWorksheet($expectedResult, ...$args): void
+    public function testBESSELJInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -70,7 +66,7 @@ public static function providerBESSELJ(): array
     /**
      * @dataProvider providerUnhappyBESSELJ
      */
-    public function testBESSELJUnhappyPath(string $expectedException, ...$args): void
+    public function testBESSELJUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselKTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselKTest.php
index 7716ab9367..8a17b5c824 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselKTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselKTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class BesselKTest extends TestCase
 
     /**
      * @dataProvider providerBESSELK
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBESSELK($expectedResult, ...$args): void
+    public function testDirectCallToBESSELK(mixed $expectedResult, mixed ...$args): void
     {
         $result = BesselK::besselK(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, self::BESSEL_PRECISION);
@@ -26,10 +26,8 @@ public function testDirectCallToBESSELK($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELK
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELKAsFormula($expectedResult, ...$args): void
+    public function testBESSELKAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -42,10 +40,8 @@ public function testBESSELKAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELK
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELKInWorksheet($expectedResult, ...$args): void
+    public function testBESSELKInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -70,7 +66,7 @@ public static function providerBESSELK(): array
     /**
      * @dataProvider providerUnhappyBESSELK
      */
-    public function testBESSELKUnhappyPath(string $expectedException, ...$args): void
+    public function testBESSELKUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselYTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselYTest.php
index 358ffe0a6f..598cd95a77 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselYTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BesselYTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class BesselYTest extends TestCase
 
     /**
      * @dataProvider providerBESSELY
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBESSELY($expectedResult, ...$args): void
+    public function testDirectCallToBESSELY(mixed $expectedResult, mixed ...$args): void
     {
         $result = BesselY::besselY(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, self::BESSEL_PRECISION);
@@ -26,10 +26,8 @@ public function testDirectCallToBESSELY($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELY
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELYAsFormula($expectedResult, ...$args): void
+    public function testBESSELYAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -42,10 +40,8 @@ public function testBESSELYAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBESSELY
-     *
-     * @param mixed $expectedResult
      */
-    public function testBESSELYInWorksheet($expectedResult, ...$args): void
+    public function testBESSELYInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -70,7 +66,7 @@ public static function providerBESSELY(): array
     /**
      * @dataProvider providerUnhappyBESSELY
      */
-    public function testBESSELYUnhappyPath(string $expectedException, ...$args): void
+    public function testBESSELYUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2DecTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2DecTest.php
index 1c096bd10e..28589bcdde 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2DecTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2DecTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Bin2DecTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerBIN2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBIN2DEC($expectedResult, ...$args): void
+    public function testDirectCallToBIN2DEC(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertBinary::toDecimal(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerBIN2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2DECAsFormula($expectedResult, ...$args): void
+    public function testBIN2DECAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testBIN2DECAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBIN2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2DECInWorksheet($expectedResult, ...$args): void
+    public function testBIN2DECInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerBIN2DEC(): array
     /**
      * @dataProvider providerUnhappyBIN2DEC
      */
-    public function testBIN2DECUnhappyPath(string $expectedException, ...$args): void
+    public function testBIN2DECUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyBIN2DEC(): array
 
     /**
      * @dataProvider providerBIN2DECOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2DECOds($expectedResult, ...$args): void
+    public function testBIN2DECOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2HexTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2HexTest.php
index ecb40132c1..45fb5de859 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2HexTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2HexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Bin2HexTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerBIN2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBIN2HEX($expectedResult, ...$args): void
+    public function testDirectCallToBIN2HEX(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertBinary::toHex(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerBIN2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2HEXAsFormula($expectedResult, ...$args): void
+    public function testBIN2HEXAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testBIN2HEXAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBIN2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2HEXInWorksheet($expectedResult, ...$args): void
+    public function testBIN2HEXInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerBIN2HEX(): array
     /**
      * @dataProvider providerUnhappyBIN2HEX
      */
-    public function testBIN2HEXUnhappyPath(string $expectedException, ...$args): void
+    public function testBIN2HEXUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyBIN2HEX(): array
 
     /**
      * @dataProvider providerBIN2HEXOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2HEXOds($expectedResult, ...$args): void
+    public function testBIN2HEXOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2OctTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2OctTest.php
index 95d9bcaab0..ecc6a033c4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2OctTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Bin2OctTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Bin2OctTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerBIN2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBIN2OCT($expectedResult, ...$args): void
+    public function testDirectCallToBIN2OCT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertBinary::toOctal(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerBIN2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2OCTAsFormula($expectedResult, ...$args): void
+    public function testBIN2OCTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testBIN2OCTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBIN2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2OCTInWorksheet($expectedResult, ...$args): void
+    public function testBIN2OCTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerBIN2OCT(): array
     /**
      * @dataProvider providerUnhappyBIN2OCT
      */
-    public function testBIN2OCTUnhappyPath(string $expectedException, ...$args): void
+    public function testBIN2OCTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyBIN2OCT(): array
 
     /**
      * @dataProvider providerBIN2OCTOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testBIN2OCTOds($expectedResult, ...$args): void
+    public function testBIN2OCTOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitAndTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitAndTest.php
index 7af8566440..047ec142ce 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitAndTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitAndTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class BitAndTest extends TestCase
 {
     /**
      * @dataProvider providerBITAND
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBITAND($expectedResult, ...$args): void
+    public function testDirectCallToBITAND(mixed $expectedResult, mixed ...$args): void
     {
         $result = BitWise::BITAND(...$args);
         self::assertSame($expectedResult, $result);
@@ -24,10 +24,8 @@ public function testDirectCallToBITAND($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITAND
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITANDAsFormula($expectedResult, ...$args): void
+    public function testBITANDAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testBITANDAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITAND
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITANDInWorksheet($expectedResult, ...$args): void
+    public function testBITANDInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerBITAND(): array
     /**
      * @dataProvider providerUnhappyBITAND
      */
-    public function testBITANDUnhappyPath(string $expectedException, ...$args): void
+    public function testBITANDUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitLShiftTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitLShiftTest.php
index c02ddad7e2..3a21e3f1a6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitLShiftTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitLShiftTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class BitLShiftTest extends TestCase
 {
     /**
      * @dataProvider providerBITLSHIFT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBITLSHIFT($expectedResult, ...$args): void
+    public function testDirectCallToBITLSHIFT(mixed $expectedResult, mixed ...$args): void
     {
         $result = BitWise::BITLSHIFT(...$args);
         self::assertSame($expectedResult, $result);
@@ -24,10 +24,8 @@ public function testDirectCallToBITLSHIFT($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITLSHIFT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITLSHIFTAsFormula($expectedResult, ...$args): void
+    public function testBITLSHIFTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testBITLSHIFTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITLSHIFT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITLSHIFTInWorksheet($expectedResult, ...$args): void
+    public function testBITLSHIFTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerBITLSHIFT(): array
     /**
      * @dataProvider providerUnhappyBITLSHIFT
      */
-    public function testBITLSHIFTUnhappyPath(string $expectedException, ...$args): void
+    public function testBITLSHIFTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitOrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitOrTest.php
index 98b06adea2..b697e91169 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitOrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitOrTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class BitOrTest extends TestCase
 {
     /**
      * @dataProvider providerBITOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBITOR($expectedResult, ...$args): void
+    public function testDirectCallToBITOR(mixed $expectedResult, mixed ...$args): void
     {
         $result = BitWise::BITOR(...$args);
         self::assertSame($expectedResult, $result);
@@ -24,10 +24,8 @@ public function testDirectCallToBITOR($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITORAsFormula($expectedResult, ...$args): void
+    public function testBITORAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testBITORAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITORInWorksheet($expectedResult, ...$args): void
+    public function testBITORInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerBITOR(): array
     /**
      * @dataProvider providerUnhappyBITOR
      */
-    public function testBITORUnhappyPath(string $expectedException, ...$args): void
+    public function testBITORUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitRShiftTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitRShiftTest.php
index 1f84b62c66..46f8668864 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitRShiftTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitRShiftTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class BitRShiftTest extends TestCase
 {
     /**
      * @dataProvider providerBITRSHIFT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBITRSHIFT($expectedResult, ...$args): void
+    public function testDirectCallToBITRSHIFT(mixed $expectedResult, mixed ...$args): void
     {
         $result = BitWise::BITRSHIFT(...$args);
         self::assertSame($expectedResult, $result);
@@ -24,10 +24,8 @@ public function testDirectCallToBITRSHIFT($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITRSHIFT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITRSHIFTAsFormula($expectedResult, ...$args): void
+    public function testBITRSHIFTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testBITRSHIFTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITRSHIFT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITRSHIFTInWorksheet($expectedResult, ...$args): void
+    public function testBITRSHIFTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerBITRSHIFT(): array
     /**
      * @dataProvider providerUnhappyBITRSHIFT
      */
-    public function testBITRSHIFTUnhappyPath(string $expectedException, ...$args): void
+    public function testBITRSHIFTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitXorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitXorTest.php
index 747c44e7f0..b62c9cc9c5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitXorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/BitXorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class BitXorTest extends TestCase
 {
     /**
      * @dataProvider providerBITXOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToBITXOR($expectedResult, ...$args): void
+    public function testDirectCallToBITXOR(mixed $expectedResult, mixed ...$args): void
     {
         $result = BitWise::BITXOR(...$args);
         self::assertSame($expectedResult, $result);
@@ -24,10 +24,8 @@ public function testDirectCallToBITXOR($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITXOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITXORAsFormula($expectedResult, ...$args): void
+    public function testBITXORAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -40,10 +38,8 @@ public function testBITXORAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerBITXOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testBITXORInWorksheet($expectedResult, ...$args): void
+    public function testBITXORInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -68,7 +64,7 @@ public static function providerBITXOR(): array
     /**
      * @dataProvider providerUnhappyBITXOR
      */
-    public function testBITXORUnhappyPath(string $expectedException, ...$args): void
+    public function testBITXORUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ComplexTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ComplexTest.php
index 647b63fa0c..93e2352f64 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ComplexTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ComplexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,8 @@ class ComplexTest extends TestCase
 {
     /**
      * @dataProvider providerCOMPLEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToCOMPLEX($expectedResult, ...$args): void
+    public function testDirectCallToCOMPLEX(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Complex::complex(...$args);
@@ -29,10 +29,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerCOMPLEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOMPLEXAsFormula($expectedResult, ...$args): void
+    public function testCOMPLEXAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -45,10 +43,8 @@ public function testCOMPLEXAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerCOMPLEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOMPLEXInWorksheet($expectedResult, ...$args): void
+    public function testCOMPLEXInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ConvertUoMTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ConvertUoMTest.php
index 0175b13277..fd9b7bca36 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ConvertUoMTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ConvertUoMTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -45,10 +47,8 @@ public function testGetBinaryConversionMultipliers(): void
 
     /**
      * @dataProvider providerCONVERTUOM
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToCONVERTUOM($expectedResult, ...$args): void
+    public function testDirectCallToCONVERTUOM(mixed $expectedResult, mixed ...$args): void
     {
         $result = ConvertUOM::convert(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, self::UOM_PRECISION);
@@ -56,10 +56,8 @@ public function testDirectCallToCONVERTUOM($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerCONVERTUOM
-     *
-     * @param mixed $expectedResult
      */
-    public function testCONVERTUOMAsFormula($expectedResult, ...$args): void
+    public function testCONVERTUOMAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -72,10 +70,8 @@ public function testCONVERTUOMAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerCONVERTUOM
-     *
-     * @param mixed $expectedResult
      */
-    public function testCONVERTUOMInWorksheet($expectedResult, ...$args): void
+    public function testCONVERTUOMInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -100,7 +96,7 @@ public static function providerCONVERTUOM(): array
     /**
      * @dataProvider providerUnhappyCONVERTUOM
      */
-    public function testCONVERTUOMUnhappyPath(string $expectedException, ...$args): void
+    public function testCONVERTUOMUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2BinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2BinTest.php
index c9f16d4ff8..02212732fc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2BinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2BinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class Dec2BinTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -29,10 +28,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerDEC2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDEC2BIN($expectedResult, ...$args): void
+    public function testDirectCallToDEC2BIN(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertDecimal::toBinary(...$args);
@@ -46,10 +43,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerDEC2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2BINAsFormula($expectedResult, ...$args): void
+    public function testDEC2BINAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -62,10 +57,8 @@ public function testDEC2BINAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDEC2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2BINInWorksheet($expectedResult, ...$args): void
+    public function testDEC2BINInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -90,7 +83,7 @@ public static function providerDEC2BIN(): array
     /**
      * @dataProvider providerUnhappyDEC2BIN
      */
-    public function testDEC2BINUnhappyPath(string $expectedException, ...$args): void
+    public function testDEC2BINUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -117,10 +110,8 @@ public static function providerUnhappyDEC2BIN(): array
 
     /**
      * @dataProvider providerDEC2BINOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2BINOds($expectedResult, ...$args): void
+    public function testDEC2BINOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2HexTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2HexTest.php
index d2b5608f1e..3ea9ad7826 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2HexTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2HexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class Dec2HexTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -29,10 +28,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerDEC2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDEC2HEX($expectedResult, ...$args): void
+    public function testDirectCallToDEC2HEX(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertDecimal::toHex(...$args);
@@ -46,10 +43,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerDEC2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2HEXAsFormula($expectedResult, ...$args): void
+    public function testDEC2HEXAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -62,10 +57,8 @@ public function testDEC2HEXAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDEC2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2HEXInWorksheet($expectedResult, ...$args): void
+    public function testDEC2HEXInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -90,7 +83,7 @@ public static function providerDEC2HEX(): array
     /**
      * @dataProvider providerUnhappyDEC2HEX
      */
-    public function testDEC2HEXUnhappyPath(string $expectedException, ...$args): void
+    public function testDEC2HEXUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -117,10 +110,8 @@ public static function providerUnhappyDEC2HEX(): array
 
     /**
      * @dataProvider providerDEC2HEXOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2HEXOds($expectedResult, ...$args): void
+    public function testDEC2HEXOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2OctTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2OctTest.php
index f5706a3fd1..869b5b9a41 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2OctTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Dec2OctTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@
 
 class Dec2OctTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -29,10 +28,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerDEC2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDEC2OCT($expectedResult, ...$args): void
+    public function testDirectCallToDEC2OCT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertDecimal::toOctal(...$args);
@@ -46,10 +43,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerDEC2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2OCTAsFormula($expectedResult, ...$args): void
+    public function testDEC2OCTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -62,10 +57,8 @@ public function testDEC2OCTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDEC2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2OCTInWorksheet($expectedResult, ...$args): void
+    public function testDEC2OCTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -90,7 +83,7 @@ public static function providerDEC2OCT(): array
     /**
      * @dataProvider providerUnhappyDEC2OCT
      */
-    public function testDEC2OCTUnhappyPath(string $expectedException, ...$args): void
+    public function testDEC2OCTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -117,10 +110,8 @@ public static function providerUnhappyDEC2OCT(): array
 
     /**
      * @dataProvider providerDEC2OCTOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEC2OCTOds($expectedResult, ...$args): void
+    public function testDEC2OCTOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/DeltaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/DeltaTest.php
index d2f211f039..6824a5e425 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/DeltaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/DeltaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class DeltaTest extends TestCase
 {
     /**
      * @dataProvider providerDELTA
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToDELTA($expectedResult, ...$args): void
+    public function testDirectCallToDELTA(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Compare::delta(...$args);
@@ -25,10 +25,8 @@ public function testDirectCallToDELTA($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDELTA
-     *
-     * @param mixed $expectedResult
      */
-    public function testDELTAAsFormula($expectedResult, ...$args): void
+    public function testDELTAAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -41,10 +39,8 @@ public function testDELTAAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerDELTA
-     *
-     * @param mixed $expectedResult
      */
-    public function testDELTAInWorksheet($expectedResult, ...$args): void
+    public function testDELTAInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -69,7 +65,7 @@ public static function providerDELTA(): array
     /**
      * @dataProvider providerUnhappyDELTA
      */
-    public function testDELTAUnhappyPath(string $expectedException, ...$args): void
+    public function testDELTAUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfCTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfCTest.php
index 834ad3d145..fa163bce6f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfCTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfCTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class ErfCTest extends TestCase
 
     /**
      * @dataProvider providerERFC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToERFC($expectedResult, ...$args): void
+    public function testDirectCallToERFC(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ErfC::ERFC(...$args);
@@ -27,10 +27,8 @@ public function testDirectCallToERFC($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerERFC
-     *
-     * @param mixed $expectedResult
      */
-    public function testERFCAsFormula($expectedResult, ...$args): void
+    public function testERFCAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -43,10 +41,8 @@ public function testERFCAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerERFC
-     *
-     * @param mixed $expectedResult
      */
-    public function testERFCInWorksheet($expectedResult, ...$args): void
+    public function testERFCInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -71,7 +67,7 @@ public static function providerERFC(): array
     /**
      * @dataProvider providerUnhappyERFC
      */
-    public function testERFCUnhappyPath(string $expectedException, ...$args): void
+    public function testERFCUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfPreciseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfPreciseTest.php
index 074f33d1a3..0f144bcdd9 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfPreciseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfPreciseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -14,10 +16,8 @@ class ErfPreciseTest extends TestCase
 
     /**
      * @dataProvider providerERFPRECISE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToERFPRECISE($expectedResult, ...$args): void
+    public function testDirectCallToERFPRECISE(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Erf::ERFPRECISE(...$args);
@@ -26,10 +26,8 @@ public function testDirectCallToERFPRECISE($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerERFPRECISE
-     *
-     * @param mixed $expectedResult
      */
-    public function testERFPRECISEAsFormula($expectedResult, ...$args): void
+    public function testERFPRECISEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -42,10 +40,8 @@ public function testERFPRECISEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerERFPRECISE
-     *
-     * @param mixed $expectedResult
      */
-    public function testERFPRECISEInWorksheet($expectedResult, ...$args): void
+    public function testERFPRECISEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfTest.php
index 19bc2fdb44..b5c7c63845 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ErfTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class ErfTest extends TestCase
 
     /**
      * @dataProvider providerERF
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToERF($expectedResult, ...$args): void
+    public function testDirectCallToERF(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Erf::erf(...$args);
@@ -27,10 +27,8 @@ public function testDirectCallToERF($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerERF
-     *
-     * @param mixed $expectedResult
      */
-    public function testERFAsFormula($expectedResult, ...$args): void
+    public function testERFAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -43,10 +41,8 @@ public function testERFAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerERF
-     *
-     * @param mixed $expectedResult
      */
-    public function testERFInWorksheet($expectedResult, ...$args): void
+    public function testERFInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -71,7 +67,7 @@ public static function providerERF(): array
     /**
      * @dataProvider providerUnhappyERF
      */
-    public function testERFUnhappyPath(string $expectedException, ...$args): void
+    public function testERFUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/GeStepTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/GeStepTest.php
index 2ccadb82fc..768cc71291 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/GeStepTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/GeStepTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,8 @@ class GeStepTest extends TestCase
 {
     /**
      * @dataProvider providerGESTEP
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToGESTEP($expectedResult, ...$args): void
+    public function testDirectCallToGESTEP(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Compare::geStep(...$args);
@@ -25,10 +25,8 @@ public function testDirectCallToGESTEP($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerGESTEP
-     *
-     * @param mixed $expectedResult
      */
-    public function testGESTEPAsFormula($expectedResult, ...$args): void
+    public function testGESTEPAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -41,10 +39,8 @@ public function testGESTEPAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerGESTEP
-     *
-     * @param mixed $expectedResult
      */
-    public function testGESTEPInWorksheet($expectedResult, ...$args): void
+    public function testGESTEPInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -69,7 +65,7 @@ public static function providerGESTEP(): array
     /**
      * @dataProvider providerUnhappyGESTEP
      */
-    public function testGESTEPUnhappyPath(string $expectedException, ...$args): void
+    public function testGESTEPUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2BinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2BinTest.php
index a145eb5add..fca419fe6a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2BinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2BinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Hex2BinTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerHEX2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToHEX2BIN($expectedResult, ...$args): void
+    public function testDirectCallToHEX2BIN(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertHex::toBinary(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerHEX2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2BINAsFormula($expectedResult, ...$args): void
+    public function testHEX2BINAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testHEX2BINAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerHEX2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2BINInWorksheet($expectedResult, ...$args): void
+    public function testHEX2BINInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerHEX2BIN(): array
     /**
      * @dataProvider providerUnhappyHEX2BIN
      */
-    public function testHEX2BINUnhappyPath(string $expectedException, ...$args): void
+    public function testHEX2BINUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyHEX2BIN(): array
 
     /**
      * @dataProvider providerHEX2BINOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2BINOds($expectedResult, ...$args): void
+    public function testHEX2BINOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2DecTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2DecTest.php
index f115d9b61e..d3822810f5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2DecTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2DecTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Hex2DecTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerHEX2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToHEX2DEC($expectedResult, ...$args): void
+    public function testDirectCallToHEX2DEC(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertHex::toDecimal(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerHEX2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2DECAsFormula($expectedResult, ...$args): void
+    public function testHEX2DECAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testHEX2DECAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerHEX2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2DECInWorksheet($expectedResult, ...$args): void
+    public function testHEX2DECInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerHEX2DEC(): array
     /**
      * @dataProvider providerUnhappyHEX2DEC
      */
-    public function testHEX2DECUnhappyPath(string $expectedException, ...$args): void
+    public function testHEX2DECUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyHEX2DEC(): array
 
     /**
      * @dataProvider providerHEX2DECOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2DECOds($expectedResult, ...$args): void
+    public function testHEX2DECOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2OctTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2OctTest.php
index 12ddf9a3d2..b227f48725 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2OctTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Hex2OctTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Hex2OctTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerHEX2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToHEX2OCT($expectedResult, ...$args): void
+    public function testDirectCallToHEX2OCT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertHex::toOctal(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerHEX2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2OCTAsFormula($expectedResult, ...$args): void
+    public function testHEX2OCTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testHEX2OCTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerHEX2OCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2OCTInWorksheet($expectedResult, ...$args): void
+    public function testHEX2OCTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerHEX2OCT(): array
     /**
      * @dataProvider providerUnhappyHEX2OCT
      */
-    public function testHEX2OCTUnhappyPath(string $expectedException, ...$args): void
+    public function testHEX2OCTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyHEX2OCT(): array
 
     /**
      * @dataProvider providerHEX2OCTOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testHEX2OCTOds($expectedResult, ...$args): void
+    public function testHEX2OCTOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImAbsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImAbsTest.php
index 959e0f1642..ac879162c4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImAbsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImAbsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,8 @@ class ImAbsTest extends TestCase
 
     /**
      * @dataProvider providerIMABS
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMABS($expectedResult, ...$args): void
+    public function testDirectCallToIMABS(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMABS(...$args);
@@ -27,10 +27,8 @@ public function testDirectCallToIMABS($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMABS
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMABSAsFormula($expectedResult, ...$args): void
+    public function testIMABSAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -43,10 +41,8 @@ public function testIMABSAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMABS
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMABSInWorksheet($expectedResult, ...$args): void
+    public function testIMABSInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -71,7 +67,7 @@ public static function providerIMABS(): array
     /**
      * @dataProvider providerUnhappyIMABS
      */
-    public function testIMABSUnhappyPath(string $expectedException, ...$args): void
+    public function testIMABSUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImArgumentTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImArgumentTest.php
index 78de3fec37..ef8c2dde6e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImArgumentTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImArgumentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -21,10 +23,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMARGUMENT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMARGUMENT($expectedResult, ...$args): void
+    public function testDirectCallToIMARGUMENT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMARGUMENT(...$args);
@@ -33,10 +33,8 @@ public function testDirectCallToIMARGUMENT($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMARGUMENT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMARGUMENTAsFormula($expectedResult, ...$args): void
+    public function testIMARGUMENTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -49,10 +47,8 @@ public function testIMARGUMENTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMARGUMENT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMARGUMENTInWorksheet($expectedResult, ...$args): void
+    public function testIMARGUMENTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -77,7 +73,7 @@ public static function providerIMARGUMENT(): array
     /**
      * @dataProvider providerUnhappyIMARGUMENT
      */
-    public function testIMARGUMENTUnhappyPath(string $expectedException, ...$args): void
+    public function testIMARGUMENTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImConjugateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImConjugateTest.php
index 7ae6f6c833..a944227f44 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImConjugateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImConjugateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImConjugateTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMCONJUGATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMCONJUGATE($expectedResult, ...$args): void
+    public function testDirectCallToIMCONJUGATE(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMCONJUGATE(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMCONJUGATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCONJUGATEAsFormula($expectedResult, ...$args): void
+    public function testIMCONJUGATEAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMCONJUGATEAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMCONJUGATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCONJUGATEInWorksheet($expectedResult, ...$args): void
+    public function testIMCONJUGATEInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMCONJUGATE(): array
     /**
      * @dataProvider providerUnhappyIMCONJUGATE
      */
-    public function testIMCONJUGATEUnhappyPath(string $expectedException, ...$args): void
+    public function testIMCONJUGATEUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCosTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCosTest.php
index 926e7d8102..26f721d68d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCosTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCosTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImCosTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMCOS
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMCOS($expectedResult, ...$args): void
+    public function testDirectCallToIMCOS(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMCOS(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMCOS
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCOSAsFormula($expectedResult, ...$args): void
+    public function testIMCOSAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMCOSAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMCOS
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCOSInWorksheet($expectedResult, ...$args): void
+    public function testIMCOSInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMCOS(): array
     /**
      * @dataProvider providerUnhappyIMCOS
      */
-    public function testIMCOSUnhappyPath(string $expectedException, ...$args): void
+    public function testIMCOSUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCoshTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCoshTest.php
index 77ddef8ac3..a23fd7a044 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCoshTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCoshTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImCoshTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMCOSH
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMCOSH($expectedResult, ...$args): void
+    public function testDirectCallToIMCOSH(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMCOSH(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMCOSH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCOSHAsFormula($expectedResult, ...$args): void
+    public function testIMCOSHAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMCOSHAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMCOSH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCOSHInWorksheet($expectedResult, ...$args): void
+    public function testIMCOSHInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMCOSH(): array
     /**
      * @dataProvider providerUnhappyIMCOSH
      */
-    public function testIMCOSHUnhappyPath(string $expectedException, ...$args): void
+    public function testIMCOSHUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCotTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCotTest.php
index 1ed3667a95..a79fb2f754 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCotTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCotTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImCotTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMCOT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMCOT($expectedResult, ...$args): void
+    public function testDirectCallToIMCOT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMCOT(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMCOT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCOTAsFormula($expectedResult, ...$args): void
+    public function testIMCOTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMCOTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMCOT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCOTInWorksheet($expectedResult, ...$args): void
+    public function testIMCOTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMCOT(): array
     /**
      * @dataProvider providerUnhappyIMCOT
      */
-    public function testIMCOTUnhappyPath(string $expectedException, ...$args): void
+    public function testIMCOTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCscTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCscTest.php
index 6029b104d5..0e469566d2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCscTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCscTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImCscTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMCSC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMCSC($expectedResult, ...$args): void
+    public function testDirectCallToIMCSC(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMCSC(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMCSC
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCSCAsFormula($expectedResult, ...$args): void
+    public function testIMCSCAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMCSCAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMCSC
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCSCInWorksheet($expectedResult, ...$args): void
+    public function testIMCSCInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMCSC(): array
     /**
      * @dataProvider providerUnhappyIMCSC
      */
-    public function testIMCSCUnhappyPath(string $expectedException, ...$args): void
+    public function testIMCSCUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCschTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCschTest.php
index 565f3fbf0e..57765ca6ec 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCschTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImCschTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImCschTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMCSCH
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMCSCH($expectedResult, ...$args): void
+    public function testDirectCallToIMCSCH(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMCSCH(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMCSCH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCSCHAsFormula($expectedResult, ...$args): void
+    public function testIMCSCHAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMCSCHAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMCSCH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMCSCHInWorksheet($expectedResult, ...$args): void
+    public function testIMCSCHInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMCSCH(): array
     /**
      * @dataProvider providerUnhappyIMCSCH
      */
-    public function testIMCSCHUnhappyPath(string $expectedException, ...$args): void
+    public function testIMCSCHUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImDivTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImDivTest.php
index d42baa1f76..635b566f5a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImDivTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImDivTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImDivTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMDIV
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMDIV($expectedResult, ...$args): void
+    public function testDirectCallToIMDIV(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexOperations::IMDIV(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMDIV
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMDIVAsFormula($expectedResult, ...$args): void
+    public function testIMDIVAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMDIVAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMDIV
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMDIVInWorksheet($expectedResult, ...$args): void
+    public function testIMDIVInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMDIV(): array
     /**
      * @dataProvider providerUnhappyIMDIV
      */
-    public function testIMDIVUnhappyPath(string $expectedException, ...$args): void
+    public function testIMDIVUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImExpTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImExpTest.php
index 7a86ab4712..53d08ab6f0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImExpTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImExpTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImExpTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMEXP
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMEXP($expectedResult, ...$args): void
+    public function testDirectCallToIMEXP(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMEXP(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMEXP
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMEXPAsFormula($expectedResult, ...$args): void
+    public function testIMEXPAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMEXPAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMEXP
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMEXPInWorksheet($expectedResult, ...$args): void
+    public function testIMEXPInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMEXP(): array
     /**
      * @dataProvider providerUnhappyIMEXP
      */
-    public function testIMEXPUnhappyPath(string $expectedException, ...$args): void
+    public function testIMEXPUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLnTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLnTest.php
index 1dc27ca727..9c4448b668 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLnTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImLnTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMLN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMLN($expectedResult, ...$args): void
+    public function testDirectCallToIMLN(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMLN(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMLN
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMLNAsFormula($expectedResult, ...$args): void
+    public function testIMLNAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMLNAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMLN
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMLNInWorksheet($expectedResult, ...$args): void
+    public function testIMLNInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMLN(): array
     /**
      * @dataProvider providerUnhappyIMLN
      */
-    public function testIMLNUnhappyPath(string $expectedException, ...$args): void
+    public function testIMLNUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog10Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog10Test.php
index 77ec963370..7d0042999e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog10Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog10Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImLog10Test extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMLOG10
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMLOG10($expectedResult, ...$args): void
+    public function testDirectCallToIMLOG10(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMLOG10(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMLOG10
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMLOG10AsFormula($expectedResult, ...$args): void
+    public function testIMLOG10AsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMLOG10AsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMLOG10
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMLOG10InWorksheet($expectedResult, ...$args): void
+    public function testIMLOG10InWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMLOG10(): array
     /**
      * @dataProvider providerUnhappyIMLOG10
      */
-    public function testIMLOG10UnhappyPath(string $expectedException, ...$args): void
+    public function testIMLOG10UnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog2Test.php
index 37313639f5..19ed1c6229 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImLog2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImLog2Test extends TestCase
 {
     const COMPLEX_PRECISION = 1E-8;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMLOG2
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMLOG2($expectedResult, ...$args): void
+    public function testDirectCallToIMLOG2(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMLOG2(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMLOG2
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMLOG2AsFormula($expectedResult, ...$args): void
+    public function testIMLOG2AsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMLOG2AsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMLOG2
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMLOG2InWorksheet($expectedResult, ...$args): void
+    public function testIMLOG2InWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMLOG2(): array
     /**
      * @dataProvider providerUnhappyIMLOG2
      */
-    public function testIMLOG2UnhappyPath(string $expectedException, ...$args): void
+    public function testIMLOG2UnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImPowerTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImPowerTest.php
index 6a652c221f..f4f80ee9eb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImPowerTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImPowerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImPowerTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMPOWER
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMPOWER($expectedResult, ...$args): void
+    public function testDirectCallToIMPOWER(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMPOWER(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMPOWER
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMPOWERAsFormula($expectedResult, ...$args): void
+    public function testIMPOWERAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMPOWERAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMPOWER
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMPOWERInWorksheet($expectedResult, ...$args): void
+    public function testIMPOWERInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMPOWER(): array
     /**
      * @dataProvider providerUnhappyIMPOWER
      */
-    public function testIMPOWERUnhappyPath(string $expectedException, ...$args): void
+    public function testIMPOWERUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImProductTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImProductTest.php
index 3c6462a253..472cb78685 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImProductTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImProductTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImProductTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMPRODUCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMPRODUCT($expectedResult, ...$args): void
+    public function testDirectCallToIMPRODUCT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexOperations::IMPRODUCT(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMPRODUCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMPRODUCTAsFormula($expectedResult, ...$args): void
+    public function testIMPRODUCTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMPRODUCTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMPRODUCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMPRODUCTInWorksheet($expectedResult, ...$args): void
+    public function testIMPRODUCTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMPRODUCT(): array
     /**
      * @dataProvider providerUnhappyIMPRODUCT
      */
-    public function testIMPRODUCTUnhappyPath(string $expectedException, ...$args): void
+    public function testIMPRODUCTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImRealTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImRealTest.php
index c4db9094c0..185073c353 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImRealTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImRealTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -21,10 +23,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMREAL
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMREAL($expectedResult, ...$args): void
+    public function testDirectCallToIMREAL(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Complex::IMREAL(...$args);
@@ -33,10 +33,8 @@ public function testDirectCallToIMREAL($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMREAL
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMREALAsFormula($expectedResult, ...$args): void
+    public function testIMREALAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -49,10 +47,8 @@ public function testIMREALAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMREAL
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMREALInWorksheet($expectedResult, ...$args): void
+    public function testIMREALInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -77,7 +73,7 @@ public static function providerIMREAL(): array
     /**
      * @dataProvider providerUnhappyIMREAL
      */
-    public function testIMREALUnhappyPath(string $expectedException, ...$args): void
+    public function testIMREALUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSecTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSecTest.php
index aebbda5e27..5a432cb8ca 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSecTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSecTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSecTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSEC($expectedResult, ...$args): void
+    public function testDirectCallToIMSEC(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMSEC(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSECAsFormula($expectedResult, ...$args): void
+    public function testIMSECAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSECAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSECInWorksheet($expectedResult, ...$args): void
+    public function testIMSECInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSEC(): array
     /**
      * @dataProvider providerUnhappyIMSEC
      */
-    public function testIMSECUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSECUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSechTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSechTest.php
index 223a9a416f..cc62f31142 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSechTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSechTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSechTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSECH
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSECH($expectedResult, ...$args): void
+    public function testDirectCallToIMSECH(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMSECH(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSECH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSECHAsFormula($expectedResult, ...$args): void
+    public function testIMSECHAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSECHAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSECH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSECHInWorksheet($expectedResult, ...$args): void
+    public function testIMSECHInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSECH(): array
     /**
      * @dataProvider providerUnhappyIMSECH
      */
-    public function testIMSECHUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSECHUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinTest.php
index 7dc5bfcd42..678229d812 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSinTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSIN($expectedResult, ...$args): void
+    public function testDirectCallToIMSIN(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMSIN(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSINAsFormula($expectedResult, ...$args): void
+    public function testIMSINAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSINAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSINInWorksheet($expectedResult, ...$args): void
+    public function testIMSINInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSIN(): array
     /**
      * @dataProvider providerUnhappyIMSIN
      */
-    public function testIMSINUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSINUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinhTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinhTest.php
index f97f8fbad3..19fc93e7be 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinhTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSinhTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSinhTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSINH
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSINH($expectedResult, ...$args): void
+    public function testDirectCallToIMSINH(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMSINH(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSINH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSINHAsFormula($expectedResult, ...$args): void
+    public function testIMSINHAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSINHAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSINH
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSINHInWorksheet($expectedResult, ...$args): void
+    public function testIMSINHInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSINH(): array
     /**
      * @dataProvider providerUnhappyIMSINH
      */
-    public function testIMSINHUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSINHUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSqrtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSqrtTest.php
index 2901ee3751..c93918cdc1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSqrtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSqrtTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSqrtTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSQRT
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSQRT($expectedResult, ...$args): void
+    public function testDirectCallToIMSQRT(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMSQRT(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSQRT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSQRTAsFormula($expectedResult, ...$args): void
+    public function testIMSQRTAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSQRTAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSQRT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSQRTInWorksheet($expectedResult, ...$args): void
+    public function testIMSQRTInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSQRT(): array
     /**
      * @dataProvider providerUnhappyIMSQRT
      */
-    public function testIMSQRTUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSQRTUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSubTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSubTest.php
index 845becd083..4457dc60d8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSubTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSubTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSubTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSUB
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSUB($expectedResult, ...$args): void
+    public function testDirectCallToIMSUB(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexOperations::IMSUB(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSUB
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSUBAsFormula($expectedResult, ...$args): void
+    public function testIMSUBAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSUBAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSUB
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSUBInWorksheet($expectedResult, ...$args): void
+    public function testIMSUBInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSUB(): array
     /**
      * @dataProvider providerUnhappyIMSUB
      */
-    public function testIMSUBUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSUBUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSumTest.php
index 6e874df44f..0dd9a1e0fb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImSumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImSumTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMSUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMSUM($expectedResult, ...$args): void
+    public function testDirectCallToIMSUM(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexOperations::IMSUM(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMSUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSUMAsFormula($expectedResult, ...$args): void
+    public function testIMSUMAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMSUMAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMSUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMSUMInWorksheet($expectedResult, ...$args): void
+    public function testIMSUMInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMSUM(): array
     /**
      * @dataProvider providerUnhappyIMSUM
      */
-    public function testIMSUMUnhappyPath(string $expectedException, ...$args): void
+    public function testIMSUMUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImTanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImTanTest.php
index a1d2ec433b..1ed1b1934b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImTanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImTanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -15,10 +17,7 @@ class ImTanTest extends TestCase
 {
     const COMPLEX_PRECISION = 1E-12;
 
-    /**
-     * @var ComplexAssert
-     */
-    private $complexAssert;
+    private \PhpOffice\PhpSpreadsheetTests\Custom\ComplexAssert $complexAssert;
 
     protected function setUp(): void
     {
@@ -28,10 +27,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMTAN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMTAN($expectedResult, ...$args): void
+    public function testDirectCallToIMTAN(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ComplexFunctions::IMTAN(...$args);
@@ -48,10 +45,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerIMTAN
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMTANAsFormula($expectedResult, ...$args): void
+    public function testIMTANAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -67,10 +62,8 @@ public function testIMTANAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMTAN
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMTANInWorksheet($expectedResult, ...$args): void
+    public function testIMTANInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -98,7 +91,7 @@ public static function providerIMTAN(): array
     /**
      * @dataProvider providerUnhappyIMTAN
      */
-    public function testIMTANUnhappyPath(string $expectedException, ...$args): void
+    public function testIMTANUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImaginaryTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImaginaryTest.php
index ac8f4eddb9..3f4e55b54e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImaginaryTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/ImaginaryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -21,10 +23,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerIMAGINARY
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToIMAGINARY($expectedResult, ...$args): void
+    public function testDirectCallToIMAGINARY(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = Complex::IMAGINARY(...$args);
@@ -33,10 +33,8 @@ public function testDirectCallToIMAGINARY($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMAGINARY
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMAGINARYAsFormula($expectedResult, ...$args): void
+    public function testIMAGINARYAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -49,10 +47,8 @@ public function testIMAGINARYAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerIMAGINARY
-     *
-     * @param mixed $expectedResult
      */
-    public function testIMAGINARYInWorksheet($expectedResult, ...$args): void
+    public function testIMAGINARYInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -77,7 +73,7 @@ public static function providerIMAGINARY(): array
     /**
      * @dataProvider providerUnhappyIMAGINARY
      */
-    public function testIMAGINARYUnhappyPath(string $expectedException, ...$args): void
+    public function testIMAGINARYUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedBitwiseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedBitwiseTest.php
index 2de8ee769c..2a0652a289 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedBitwiseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedBitwiseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Engineering;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedFunctionsTest.php
index a98ca605ed..f68ea1f2ac 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/MovedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Engineering;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2BinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2BinTest.php
index 4046f9ec46..fe0953d233 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2BinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2BinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Oct2BinTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerOCT2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToOCT2BIN($expectedResult, ...$args): void
+    public function testDirectCallToOCT2BIN(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertOctal::toBinary(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerOCT2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2BINAsFormula($expectedResult, ...$args): void
+    public function testOCT2BINAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testOCT2BINAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerOCT2BIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2BINInWorksheet($expectedResult, ...$args): void
+    public function testOCT2BINInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerOCT2BIN(): array
     /**
      * @dataProvider providerUnhappyOCT2BIN
      */
-    public function testOCT2BINUnhappyPath(string $expectedException, ...$args): void
+    public function testOCT2BINUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyOCT2BIN(): array
 
     /**
      * @dataProvider providerOCT2BINOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2BINOds($expectedResult, ...$args): void
+    public function testOCT2BINOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2DecTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2DecTest.php
index b6872f9508..c1e02fbc73 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2DecTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2DecTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Oct2DecTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerOCT2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToOCT2DEC($expectedResult, ...$args): void
+    public function testDirectCallToOCT2DEC(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertOctal::toDecimal(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerOCT2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2DECAsFormula($expectedResult, ...$args): void
+    public function testOCT2DECAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testOCT2DECAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerOCT2DEC
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2DECInWorksheet($expectedResult, ...$args): void
+    public function testOCT2DECInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerOCT2DEC(): array
     /**
      * @dataProvider providerUnhappyOCT2DEC
      */
-    public function testOCT2DECUnhappyPath(string $expectedException, ...$args): void
+    public function testOCT2DECUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyOCT2DEC(): array
 
     /**
      * @dataProvider providerOCT2DECOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2DECOds($expectedResult, ...$args): void
+    public function testOCT2DECOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2HexTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2HexTest.php
index b448e5b4ef..1a43a49947 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2HexTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Engineering/Oct2HexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Engineering;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -13,10 +15,7 @@
 
 class Oct2HexTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
@@ -30,10 +29,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerOCT2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testDirectCallToOCT2HEX($expectedResult, ...$args): void
+    public function testDirectCallToOCT2HEX(mixed $expectedResult, mixed ...$args): void
     {
         /** @scrutinizer ignore-call */
         $result = ConvertOctal::toHex(...$args);
@@ -47,10 +44,8 @@ private function trimIfQuoted(string $value): string
 
     /**
      * @dataProvider providerOCT2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2HEXAsFormula($expectedResult, ...$args): void
+    public function testOCT2HEXAsFormula(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -63,10 +58,8 @@ public function testOCT2HEXAsFormula($expectedResult, ...$args): void
 
     /**
      * @dataProvider providerOCT2HEX
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2HEXInWorksheet($expectedResult, ...$args): void
+    public function testOCT2HEXInWorksheet(mixed $expectedResult, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -91,7 +84,7 @@ public static function providerOCT2HEX(): array
     /**
      * @dataProvider providerUnhappyOCT2HEX
      */
-    public function testOCT2HEXUnhappyPath(string $expectedException, ...$args): void
+    public function testOCT2HEXUnhappyPath(string $expectedException, mixed ...$args): void
     {
         $arguments = new FormulaArguments(...$args);
 
@@ -118,10 +111,8 @@ public static function providerUnhappyOCT2HEX(): array
 
     /**
      * @dataProvider providerOCT2HEXOds
-     *
-     * @param mixed $expectedResult
      */
-    public function testOCT2HEXOds($expectedResult, ...$args): void
+    public function testOCT2HEXOds(mixed $expectedResult, mixed ...$args): void
     {
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_OPENOFFICE);
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintMTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintMTest.php
index abc22e3366..07f99cc2db 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintMTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintMTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class AccrintMTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerACCRINTM
-     *
-     * @param mixed $expectedResult
      */
-    public function testACCRINTM($expectedResult, ...$args): void
+    public function testACCRINTM(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('ACCRINTM', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintTest.php
index af87ddaefd..97bd742df1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AccrintTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class AccrintTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerACCRINT
-     *
-     * @param mixed $expectedResult
      */
-    public function testACCRINT($expectedResult, ...$args): void
+    public function testACCRINT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('ACCRINT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AllSetupTeardown.php
index 12fafa0b21..6fd236934b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AllSetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -11,10 +13,7 @@
 
 class AllSetupTeardown extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     /**
      * @var ?Spreadsheet
@@ -51,20 +50,14 @@ protected static function setGnumeric(): void
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_GNUMERIC);
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    protected function mightHaveException($expectedResult): void
+    protected function mightHaveException(mixed $expectedResult): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(CalcException::class);
         }
     }
 
-    /**
-     * @param mixed $value
-     */
-    protected function setCell(string $cell, $value): void
+    protected function setCell(string $cell, mixed $value): void
     {
         if ($value !== null) {
             if (is_string($value) && is_numeric($value)) {
@@ -98,11 +91,8 @@ protected function getSheet(): Worksheet
     /**
      * Adjust result if it is close enough to expected by ratio
      *     rather than offset.
-     *
-     * @param mixed $result
-     * @param mixed $expectedResult
      */
-    protected function adjustResult(&$result, $expectedResult): void
+    protected function adjustResult(mixed &$result, mixed $expectedResult): void
     {
         if (is_numeric($result) && is_numeric($expectedResult)) {
             if ($expectedResult != 0) {
@@ -114,10 +104,7 @@ protected function adjustResult(&$result, $expectedResult): void
         }
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    public function runTestCase(string $functionName, $expectedResult, array $args): void
+    public function runTestCase(string $functionName, mixed $expectedResult, array $args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorDegRcTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorDegRcTest.php
index 2798844427..459b7674ac 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorDegRcTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorDegRcTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class AmorDegRcTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAMORDEGRC
-     *
-     * @param mixed $expectedResult
      */
-    public function testAMORDEGRC($expectedResult, ...$args): void
+    public function testAMORDEGRC(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('AMORDEGRC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorLincTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorLincTest.php
index ddd7186430..95db9bc190 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorLincTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/AmorLincTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class AmorLincTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAMORLINC
-     *
-     * @param mixed $expectedResult
      */
-    public function testAMORLINC($expectedResult, ...$args): void
+    public function testAMORLINC(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('AMORLINC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDayBsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDayBsTest.php
index 6423b7a469..15633fd8e0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDayBsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDayBsTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CoupDayBsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUPDAYBS
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUPDAYBS($expectedResult, ...$args): void
+    public function testCOUPDAYBS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('COUPDAYBS', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysNcTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysNcTest.php
index 83e9dbbb93..7696f61f85 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysNcTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysNcTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CoupDaysNcTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUPDAYSNC
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUPDAYSNC($expectedResult, ...$args): void
+    public function testCOUPDAYSNC(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('COUPDAYSNC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysTest.php
index 2baed24299..f7ba0e7be0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupDaysTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CoupDaysTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUPDAYS
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUPDAYS($expectedResult, ...$args): void
+    public function testCOUPDAYS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('COUPDAYS', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNcdTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNcdTest.php
index 6fa58197f3..f3f04792f0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNcdTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNcdTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CoupNcdTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUPNCD
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUPNCD($expectedResult, ...$args): void
+    public function testCOUPNCD(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('COUPNCD', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNumTest.php
index a4d962af0c..86360ecb33 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupNumTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CoupNumTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUPNUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUPNUM($expectedResult, ...$args): void
+    public function testCOUPNUM(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('COUPNUM', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupPcdTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupPcdTest.php
index e7d460f7b6..8c02ea048c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupPcdTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CoupPcdTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CoupPcdTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUPPCD
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUPPCD($expectedResult, ...$args): void
+    public function testCOUPPCD(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('COUPPCD', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumIpmtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumIpmtTest.php
index 26450faac0..a27724ab8b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumIpmtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumIpmtTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CumIpmtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCUMIPMT
-     *
-     * @param mixed $expectedResult
      */
-    public function testCUMIPMT($expectedResult, ...$args): void
+    public function testCUMIPMT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('CUMIPMT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumPrincTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumPrincTest.php
index 2cc19fd695..b241c29406 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumPrincTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/CumPrincTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class CumPrincTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCUMPRINC
-     *
-     * @param mixed $expectedResult
      */
-    public function testCUMPRINC($expectedResult, ...$args): void
+    public function testCUMPRINC(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('CUMPRINC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DbTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DbTest.php
index 2ac986e761..13856c048b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DbTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DbTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class DbTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDB
-     *
-     * @param mixed $expectedResult
      */
-    public function testDB($expectedResult, ...$args): void
+    public function testDB(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('DB', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DdbTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DdbTest.php
index b2ef69a92d..5e513ed646 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DdbTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DdbTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class DdbTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDDB
-     *
-     * @param mixed $expectedResult
      */
-    public function testDDB($expectedResult, ...$args): void
+    public function testDDB(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('DDB', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DiscTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DiscTest.php
index d983ad0920..317854edc1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DiscTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DiscTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class DiscTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDISC
-     *
-     * @param mixed $expectedResult
      */
-    public function testDISC($expectedResult, ...$args): void
+    public function testDISC(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('DISC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarDeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarDeTest.php
index 56bb681a1e..c379377401 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarDeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarDeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class DollarDeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDOLLARDE
-     *
-     * @param mixed $expectedResult
      */
-    public function testDOLLARDE($expectedResult, ...$args): void
+    public function testDOLLARDE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('DOLLARDE', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarFrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarFrTest.php
index adbbaea7a9..992b5a64eb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarFrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/DollarFrTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class DollarFrTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDOLLARFR
-     *
-     * @param mixed $expectedResult
      */
-    public function testDOLLARFR($expectedResult, ...$args): void
+    public function testDOLLARFR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('DOLLARFR', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/EffectTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/EffectTest.php
index 249a5f1124..4811c64c3c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/EffectTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/EffectTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class EffectTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerEFFECT
-     *
-     * @param mixed $expectedResult
      */
-    public function testEFFECT($expectedResult, ...$args): void
+    public function testEFFECT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('EFFECT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvScheduleTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvScheduleTest.php
index 9080a38ab2..bb72492f52 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvScheduleTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvScheduleTest.php
@@ -1,16 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class FvScheduleTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFVSCHEDULE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $principal
      */
-    public function testFVSCHEDULE($expectedResult, $principal = null, ?array $schedule = null): void
+    public function testFVSCHEDULE(mixed $expectedResult, mixed $principal = null, ?array $schedule = null): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvTest.php
index 5f221940c3..1dbfee1af2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/FvTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class FvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFV
-     *
-     * @param mixed $expectedResult
      */
-    public function testFV($expectedResult, array $args): void
+    public function testFV(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('FV', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/HelpersTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/HelpersTest.php
index ed132b7e27..6cceaf423d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/HelpersTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/HelpersTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Financial\Helpers;
@@ -9,12 +11,8 @@ class HelpersTest extends TestCase
 {
     /**
      * @dataProvider providerDaysPerYear
-     *
-     * @param mixed $expectedResult
-     * @param mixed $year
-     * @param mixed $basis
      */
-    public function testDaysPerYear($expectedResult, $year, $basis): void
+    public function testDaysPerYear(mixed $expectedResult, mixed $year, mixed $basis): void
     {
         $result = Helpers::daysPerYear($year, $basis);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IPmtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IPmtTest.php
index 0af641ad16..75faf79272 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IPmtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IPmtTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class IPmtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerIPMT
-     *
-     * @param mixed $expectedResult
      */
-    public function testIPMT($expectedResult, array $args): void
+    public function testIPMT(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('IPMT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IntRateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IntRateTest.php
index 9827182f5b..fc111f1cd7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IntRateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IntRateTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class IntRateTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerINTRATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testINTRATE($expectedResult, ...$args): void
+    public function testINTRATE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('INTRATE', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IrrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IrrTest.php
index 608d8d2616..08d09c5875 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IrrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IrrTest.php
@@ -1,16 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class IrrTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerIRR
-     *
-     * @param mixed $expectedResult
-     * @param mixed $values
      */
-    public function testIRR($expectedResult, $values = null): void
+    public function testIRR(mixed $expectedResult, mixed $values = null): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IsPmtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IsPmtTest.php
index cfb4a9efed..ea085fb50c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IsPmtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/IsPmtTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class IsPmtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerISPMT
-     *
-     * @param mixed $expectedResult
      */
-    public function testISPMT($expectedResult, ...$args): void
+    public function testISPMT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('ISPMT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MirrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MirrTest.php
index c2412b8e00..d2a65dd068 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MirrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MirrTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -8,13 +10,8 @@ class MirrTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMIRR
-     *
-     * @param mixed $expectedResult
-     * @param mixed $values
-     * @param mixed $financeRate
-     * @param mixed $reinvestRate
      */
-    public function testMIRR($expectedResult, $values, $financeRate = null, $reinvestRate = null): void
+    public function testMIRR(mixed $expectedResult, mixed $values, mixed $financeRate = null, mixed $reinvestRate = null): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MovedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MovedFunctionsTest.php
index 4429c522c2..e23def8569 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MovedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/MovedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 //use PhpOffice\PhpSpreadsheet\Calculation\Functions;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NPerTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NPerTest.php
index 1fb12ed49a..302ad808fb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NPerTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NPerTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class NPerTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNPER
-     *
-     * @param mixed $expectedResult
      */
-    public function testNPER($expectedResult, array $args): void
+    public function testNPER(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('NPER', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NominalTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NominalTest.php
index fd6f5710bc..302d5a0c17 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NominalTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NominalTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class NominalTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNOMINAL
-     *
-     * @param mixed $expectedResult
      */
-    public function testNOMINAL($expectedResult, ...$args): void
+    public function testNOMINAL(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('NOMINAL', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NpvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NpvTest.php
index ed3126ae57..c43d819bdc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NpvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/NpvTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class NpvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNPV
-     *
-     * @param mixed $expectedResult
      */
-    public function testNPV($expectedResult, ...$args): void
+    public function testNPV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('NPV', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PDurationTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PDurationTest.php
index 475ac3bfb8..7c31158e14 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PDurationTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PDurationTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PDurationTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPDURATION
-     *
-     * @param mixed $expectedResult
      */
-    public function testPDURATION($expectedResult, array $args): void
+    public function testPDURATION(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('PDURATION', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PmtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PmtTest.php
index 2868b9dc3a..ae3f6ea9fe 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PmtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PmtTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PmtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPMT
-     *
-     * @param mixed $expectedResult
      */
-    public function testPMT($expectedResult, array $args): void
+    public function testPMT(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('PMT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PpmtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PpmtTest.php
index a373dab636..820d315d8c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PpmtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PpmtTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PpmtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPPMT
-     *
-     * @param mixed $expectedResult
      */
-    public function testPPMT($expectedResult, array $args): void
+    public function testPPMT(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('PPMT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceDiscTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceDiscTest.php
index ac6dca08d0..2abb6effbc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceDiscTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceDiscTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PriceDiscTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPRICEDISC
-     *
-     * @param mixed $expectedResult
      */
-    public function testPRICEDISC($expectedResult, array $args): void
+    public function testPRICEDISC(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('PRICEDISC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceMatTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceMatTest.php
index 23a0633871..a30c196b83 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceMatTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceMatTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PriceMatTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPRICEMAT
-     *
-     * @param mixed $expectedResult
      */
-    public function testPRICEMAT($expectedResult, ...$args): void
+    public function testPRICEMAT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('PRICEMAT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceTest.php
index 43f5b10c84..56328f882a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PriceTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PriceTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPRICE
-     *
-     * @param mixed $expectedResult
      */
-    public function testPRICE($expectedResult, ...$args): void
+    public function testPRICE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('PRICE', $expectedResult, $args);
     }
@@ -21,10 +21,8 @@ public static function providerPRICE(): array
 
     /**
      * @dataProvider providerPRICE3
-     *
-     * @param mixed $expectedResult
      */
-    public function testPRICE3($expectedResult, ...$args): void
+    public function testPRICE3(mixed $expectedResult, mixed ...$args): void
     {
         // These results (PRICE function with basis codes 2 and 3)
         // agree with published algorithm, LibreOffice, and Gnumeric.
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PvTest.php
index fdee2f9d55..ffdb1e25b4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/PvTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class PvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPV
-     *
-     * @param mixed $expectedResult
      */
-    public function testPV($expectedResult, array $args): void
+    public function testPV(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('PV', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RateTest.php
index 4943aed0e4..f36437395e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RateTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class RateTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRATE
-     *
-     * @param mixed $expectedResult
      */
-    public function testRATE($expectedResult, ...$args): void
+    public function testRATE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('RATE', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/ReceivedTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/ReceivedTest.php
index 648c62a6bd..d5ac3000b2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/ReceivedTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/ReceivedTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class ReceivedTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRECEIVED
-     *
-     * @param mixed $expectedResult
      */
-    public function testRECEIVED($expectedResult, ...$args): void
+    public function testRECEIVED(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('RECEIVED', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RriTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RriTest.php
index 97175014ed..ccfd7587b3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RriTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/RriTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class RriTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRRI
-     *
-     * @param mixed $expectedResult
      */
-    public function testRRI($expectedResult, array $args): void
+    public function testRRI(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('RRI', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SlnTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SlnTest.php
index acce9b3de9..abe5a7a9cf 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SlnTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SlnTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class SlnTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSLN
-     *
-     * @param mixed $expectedResult
      */
-    public function testSLN($expectedResult, array $args): void
+    public function testSLN(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('SLN', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SydTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SydTest.php
index 3cc228b45d..6b8561771c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SydTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/SydTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class SydTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSYD
-     *
-     * @param mixed $expectedResult
      */
-    public function testSYD($expectedResult, array $args): void
+    public function testSYD(mixed $expectedResult, array $args): void
     {
         $this->runTestCase('SYD', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillEqTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillEqTest.php
index bf19947859..d18aa52852 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillEqTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillEqTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class TBillEqTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTBILLEQ
-     *
-     * @param mixed $expectedResult
      */
-    public function testTBILLEQ($expectedResult, ...$args): void
+    public function testTBILLEQ(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('TBILLEQ', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillPriceTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillPriceTest.php
index 2beb00966d..c8778fc28b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillPriceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillPriceTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class TBillPriceTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTBILLPRICE
-     *
-     * @param mixed $expectedResult
      */
-    public function testTBILLPRICE($expectedResult, ...$args): void
+    public function testTBILLPRICE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('TBILLPRICE', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillYieldTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillYieldTest.php
index bdfa5a5bb0..30d58c3277 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillYieldTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/TBillYieldTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class TBillYieldTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTBILLYIELD
-     *
-     * @param mixed $expectedResult
      */
-    public function testTBILLYIELD($expectedResult, ...$args): void
+    public function testTBILLYIELD(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('TBILLYIELD', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/UsDollarTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/UsDollarTest.php
index 8eeb78fc9b..91714a169e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/UsDollarTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/UsDollarTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class UsDollarTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerUSDOLLAR
-     *
-     * @param mixed $expectedResult
      */
-    public function testUSDOLLAR($expectedResult, ...$args): void
+    public function testUSDOLLAR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('USDOLLAR', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XNpvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XNpvTest.php
index a147d71d48..a94a9210d3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XNpvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XNpvTest.php
@@ -1,18 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class XNpvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerXNPV
-     *
-     * @param mixed $expectedResult
-     * @param mixed $rate
-     * @param mixed $values
-     * @param mixed $dates
      */
-    public function testXNPV($expectedResult, $rate = null, $values = null, $dates = null): void
+    public function testXNPV(mixed $expectedResult, mixed $rate = null, mixed $values = null, mixed $dates = null): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XirrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XirrTest.php
index d454de37be..d48bd1b610 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XirrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/XirrTest.php
@@ -1,18 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class XirrTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerXIRR
-     *
-     * @param mixed $expectedResult
-     * @param mixed $values
-     * @param mixed $dates
-     * @param mixed $guess
      */
-    public function testXIRR($expectedResult, $values = null, $dates = null, $guess = null): void
+    public function testXIRR(mixed $expectedResult, mixed $values = null, mixed $dates = null, mixed $guess = null): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldDiscTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldDiscTest.php
index ec3d964191..32f8431747 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldDiscTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldDiscTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class YieldDiscTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerYIELDDISC
-     *
-     * @param mixed $expectedResult
      */
-    public function testYIELDDISC($expectedResult, ...$args): void
+    public function testYIELDDISC(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('YIELDDISC', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldMatTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldMatTest.php
index 89f9b891ea..28c5540607 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldMatTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Financial/YieldMatTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Financial;
 
 class YieldMatTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerYIELDMAT
-     *
-     * @param mixed $expectedResult
      */
-    public function testYIELDMAT($expectedResult, ...$args): void
+    public function testYIELDMAT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('YIELDMAT', $expectedResult, $args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/FormulaArguments.php b/tests/PhpSpreadsheetTests/Calculation/Functions/FormulaArguments.php
index eea1ac3dbd..d40cb1c436 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/FormulaArguments.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/FormulaArguments.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions;
 
 use PhpOffice\PhpSpreadsheet\Cell\CellAddress;
@@ -12,10 +14,7 @@ class FormulaArguments
      */
     protected array $args;
 
-    /**
-     * @param mixed ...$args
-     */
-    public function __construct(...$args)
+    public function __construct(mixed ...$args)
     {
         $this->args = $args;
     }
@@ -27,7 +26,7 @@ public function populateWorksheet(Worksheet $worksheet): string
         foreach ($this->args as $value) {
             if (is_array($value)) {
                 // We need to set a matrix in the worksheet
-                $worksheet->fromArray($value, null, $cellAddress, true);
+                $worksheet->fromArray($value, null, (string) $cellAddress, true);
                 $from = (string) $cellAddress;
                 $columns = is_array($value[0]) ? count($value[0]) : count($value);
                 $rows = is_array($value[0]) ? count($value) : 1;
@@ -45,10 +44,7 @@ public function populateWorksheet(Worksheet $worksheet): string
         return implode(',', $cells);
     }
 
-    /**
-     * @param mixed $value
-     */
-    private function matrixRows($value): string
+    private function matrixRows(array $value): string
     {
         $columns = [];
         foreach ($value as $column) {
@@ -58,10 +54,7 @@ private function matrixRows($value): string
         return implode(',', $columns);
     }
 
-    /**
-     * @param mixed $value
-     */
-    private function makeMatrix($value): string
+    private function makeMatrix(array $value): string
     {
         $matrix = [];
         foreach ($value as $row) {
@@ -75,10 +68,7 @@ private function makeMatrix($value): string
         return implode(';', $matrix);
     }
 
-    /**
-     * @param mixed $value
-     */
-    private function stringify($value): string
+    private function stringify(mixed $value): string
     {
         if (is_array($value)) {
             return '{' . $this->makeMatrix($value) . '}';
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/DeprecatedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/DeprecatedFunctionsTest.php
index ca7c75d7d0..864faf58ab 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/DeprecatedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/DeprecatedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php
index 8655ff0b9c..391b40380b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/Div0Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php
index d3e3c58bb3..c0e9eb4d02 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ErrorTypeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,11 +18,8 @@ public function testErrorTypeNoArgument(): void
 
     /**
      * @dataProvider providerErrorType
-     *
-     * @param int|string $expectedResult
-     * @param mixed $value
      */
-    public function testErrorType($expectedResult, $value): void
+    public function testErrorType(int|string $expectedResult, mixed $value): void
     {
         $result = ExcelError::type($value);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsBlankTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsBlankTest.php
index 0713e9ed00..8a047a59e3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsBlankTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsBlankTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsBlankNoArgument(): void
 
     /**
      * @dataProvider providerIsBlank
-     *
-     * @param mixed $value
      */
-    public function testIsBlank(bool $expectedResult, $value): void
+    public function testIsBlank(bool $expectedResult, mixed $value): void
     {
         $result = Value::isBlank($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrTest.php
index aff619414d..a24dde86f0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsErrNoArgument(): void
 
     /**
      * @dataProvider providerIsErr
-     *
-     * @param mixed $value
      */
-    public function testIsErr(bool $expectedResult, $value): void
+    public function testIsErr(bool $expectedResult, mixed $value): void
     {
         $result = ErrorValue::isErr($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php
index ff7f48176e..765cb8e558 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsErrorNoArgument(): void
 
     /**
      * @dataProvider providerIsError
-     *
-     * @param mixed $value
      */
-    public function testIsError(bool $expectedResult, $value): void
+    public function testIsError(bool $expectedResult, mixed $value): void
     {
         $result = ErrorValue::isError($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsEvenTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsEvenTest.php
index 685a909ec7..0ebf0ed059 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsEvenTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsEvenTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -17,11 +19,8 @@ public function testIsEvenNoArgument(): void
 
     /**
      * @dataProvider providerIsEven
-     *
-     * @param bool|string $expectedResult
-     * @param mixed $value
      */
-    public function testIsEven($expectedResult, $value): void
+    public function testIsEven(bool|string $expectedResult, mixed $value): void
     {
         $result = Value::isEven($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php
index 03e9bb70d0..9f691d1562 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsLogicalTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsLogicalTest.php
index 8dd2abb085..ea53a56dcb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsLogicalTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsLogicalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsLogicalNoArgument(): void
 
     /**
      * @dataProvider providerIsLogical
-     *
-     * @param mixed $value
      */
-    public function testIsLogical(bool $expectedResult, $value): void
+    public function testIsLogical(bool $expectedResult, mixed $value): void
     {
         $result = Value::isLogical($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNaTest.php
index 56bc49fe53..87e6be25b3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsNaNoArgument(): void
 
     /**
      * @dataProvider providerIsNa
-     *
-     * @param mixed $value
      */
-    public function testIsNa(bool $expectedResult, $value): void
+    public function testIsNa(bool $expectedResult, mixed $value): void
     {
         $result = ErrorValue::isNa($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNonTextTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNonTextTest.php
index 20a8c2c611..e84c835cc7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNonTextTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNonTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsNonTextNoArgument(): void
 
     /**
      * @dataProvider providerIsNonText
-     *
-     * @param mixed $value
      */
-    public function testIsNonText(bool $expectedResult, $value): void
+    public function testIsNonText(bool $expectedResult, mixed $value): void
     {
         $result = Value::isNonText($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNumberTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNumberTest.php
index f7341acc02..91850022cc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNumberTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsNumberTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsNumberNoArgument(): void
 
     /**
      * @dataProvider providerIsNumber
-     *
-     * @param mixed $value
      */
-    public function testIsNumber(bool $expectedResult, $value): void
+    public function testIsNumber(bool $expectedResult, mixed $value): void
     {
         $result = Value::isNumber($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsOddTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsOddTest.php
index 4510de66f9..fb94d483c0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsOddTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsOddTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -17,11 +19,8 @@ public function testIsOddNoArgument(): void
 
     /**
      * @dataProvider providerIsOdd
-     *
-     * @param bool|string $expectedResult
-     * @param mixed $value
      */
-    public function testIsOdd($expectedResult, $value): void
+    public function testIsOdd(bool|string $expectedResult, mixed $value): void
     {
         $result = Value::isOdd($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsRefTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsRefTest.php
index c048d8c506..962e71fa99 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsRefTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsRefTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsTextTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsTextTest.php
index f40d9013d3..0fee579c09 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsTextTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/IsTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -16,10 +18,8 @@ public function testIsTextNoArgument(): void
 
     /**
      * @dataProvider providerIsText
-     *
-     * @param mixed $value
      */
-    public function testIsText(bool $expectedResult, $value): void
+    public function testIsText(bool $expectedResult, mixed $value): void
     {
         $result = Value::isText($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NTest.php
index 13d50412d2..2224ad87ae 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\Value;
@@ -15,11 +17,8 @@ public function testNNoArgument(): void
 
     /**
      * @dataProvider providerN
-     *
-     * @param mixed $expectedResult
-     * @param number|string $value
      */
-    public function testN($expectedResult, $value): void
+    public function testN(mixed $expectedResult, mixed $value): void
     {
         $result = Value::asNumber($value);
         self::assertEqualsWithDelta($expectedResult, $result, 1.0e-12);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php
index 471619f31e..f8b8c92f43 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php
index 107e268c42..61953826a8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NameTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php
index 58f974888f..f4e49ae55f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php
index 65ce5ddbd5..0a5d91eed4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/NullTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php
index 7a8a33deb9..d5b3df5e8e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/RefTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/TypeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/TypeTest.php
index f3022712c7..4b36ccd6db 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/TypeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/TypeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\Value;
@@ -15,10 +17,8 @@ public function testTypeNoArgument(): void
 
     /**
      * @dataProvider providerTYPE
-     *
-     * @param mixed $value
      */
-    public function testTYPE(int $expectedResult, $value): void
+    public function testTYPE(int $expectedResult, mixed $value): void
     {
         $result = Value::type($value);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php
index 5ab07bd76f..7aecf2d940 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Information/ValueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Information;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AllSetupTeardown.php
index 34432c6a15..709535dc9c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AllSetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -11,10 +13,7 @@
 
 class AllSetupTeardown extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     /**
      * @var ?Spreadsheet
@@ -51,20 +50,14 @@ protected static function setGnumeric(): void
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_GNUMERIC);
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    protected function mightHaveException($expectedResult): void
+    protected function mightHaveException(mixed $expectedResult): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(CalcException::class);
         }
     }
 
-    /**
-     * @param mixed $value
-     */
-    protected function setCell(string $cell, $value): void
+    protected function setCell(string $cell, mixed $value): void
     {
         if ($value !== null) {
             if (is_string($value) && is_numeric($value)) {
@@ -95,11 +88,7 @@ protected function getSheet(): Worksheet
         return $this->sheet;
     }
 
-    /**
-     * @param mixed $expectedResult
-     * @param array $args
-     */
-    protected function runTestCase(string $functionName, $expectedResult, ...$args): void
+    protected function runTestCase(string $functionName, mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AndTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AndTest.php
index b9ad5bbe11..c9dacefd2a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AndTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/AndTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 class AndTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAND
-     *
-     * @param mixed $expectedResult
      */
-    public function testAND($expectedResult, ...$args): void
+    public function testAND(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('AND', $expectedResult, ...$args);
     }
@@ -21,11 +21,8 @@ public static function providerAND(): array
 
     /**
      * @dataProvider providerANDLiteral
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testANDLiteral($expectedResult, $formula): void
+    public function testANDLiteral(mixed $expectedResult, mixed $formula): void
     {
         $sheet = $this->getSheet();
         $sheet->getCell('A1')->setValue("=AND($formula)");
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/DeprecatedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/DeprecatedFunctionsTest.php
index 11b1beaf9a..4d0c1a8144 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/DeprecatedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/DeprecatedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Logical;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/FalseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/FalseTest.php
index e19ff38741..08ac289f08 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/FalseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/FalseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 class FalseTest extends AllSetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfErrorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfErrorTest.php
index cf0651df18..6329c9b0e8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class IfErrorTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerIFERROR
-     *
-     * @param mixed $expectedResult
      */
-    public function testIFERROR($expectedResult, ...$args): void
+    public function testIFERROR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('IFERROR', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfNaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfNaTest.php
index eab9410386..a629bd7ab1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfNaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfNaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class IfNaTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerIFNA
-     *
-     * @param mixed $expectedResult
      */
-    public function testIFNA($expectedResult, ...$args): void
+    public function testIFNA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('IFNA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfTest.php
index 914f50fd75..fc631043ae 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 class IfTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerIF
-     *
-     * @param mixed $expectedResult
      */
-    public function testIF($expectedResult, ...$args): void
+    public function testIF(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('IF', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfsTest.php
index a1ca9a2658..eeb38b9a28 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/IfsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class IfsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerIFS
-     *
-     * @param mixed $expectedResult
-     * @param mixed $args
      */
-    public function testIFS($expectedResult, ...$args): void
+    public function testIFS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('IFS', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/NotTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/NotTest.php
index 0d408ff7f3..db53b38949 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/NotTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/NotTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NotTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNOT
-     *
-     * @param mixed $expectedResult
      */
-    public function testNOT($expectedResult, ...$args): void
+    public function testNOT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('NOT', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/OrTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/OrTest.php
index 4b6368358e..6f369f5737 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/OrTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/OrTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 class OrTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testOR($expectedResult, ...$args): void
+    public function testOR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('OR', $expectedResult, ...$args);
     }
@@ -21,11 +21,8 @@ public static function providerOR(): array
 
     /**
      * @dataProvider providerORLiteral
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testORLiteral($expectedResult, $formula): void
+    public function testORLiteral(mixed $expectedResult, mixed $formula): void
     {
         $sheet = $this->getSheet();
         $sheet->getCell('A1')->setValue("=OR($formula)");
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/SwitchTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/SwitchTest.php
index 7b9c92df53..1ef186060f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/SwitchTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/SwitchTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class SwitchTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSwitch
-     *
-     * @param mixed $expectedResult
      */
-    public function testSWITCH($expectedResult, ...$args): void
+    public function testSWITCH(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('SWITCH', $expectedResult, ...$args);
     }
@@ -23,12 +23,8 @@ public static function providerSwitch(): array
 
     /**
      * @dataProvider providerSwitchArray
-     *
-     * @param mixed $expression
-     * @param mixed $value1
-     * @param mixed $value2
      */
-    public function testIfsArray(array $expectedResult, $expression, $value1, string $result1, $value2, string $result2, string $default): void
+    public function testIfsArray(array $expectedResult, mixed $expression, mixed $value1, string $result1, mixed $value2, string $result2, string $default): void
     {
         $calculation = Calculation::getInstance();
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/TrueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/TrueTest.php
index 5ce4517026..0c61e4390e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/TrueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/TrueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 class TrueTest extends AllSetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/XorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/XorTest.php
index 922bd02bb0..e319cbb4a4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/XorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Logical/XorTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Logical;
 
 class XorTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerXOR
-     *
-     * @param mixed $expectedResult
      */
-    public function testXOR($expectedResult, ...$args): void
+    public function testXOR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCase('XOR', $expectedResult, ...$args);
     }
@@ -21,11 +21,8 @@ public static function providerXOR(): array
 
     /**
      * @dataProvider providerXORLiteral
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function xtestXORLiteral($expectedResult, $formula): void
+    public function xtestXORLiteral(mixed $expectedResult, string $formula): void
     {
         $sheet = $this->getSheet();
         $sheet->getCell('A1')->setValue("=XOR($formula)");
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressInternationalTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressInternationalTest.php
index 3f2539d206..d7aa9101c6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressInternationalTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressInternationalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -7,8 +9,7 @@
 
 class AddressInternationalTest extends AllSetupTeardown
 {
-    /** @var string */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressTest.php
index 73e0d5c9c0..0bb9833ab2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AddressTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,10 +12,8 @@ class AddressTest extends TestCase
 {
     /**
      * @dataProvider providerADDRESS
-     *
-     * @param mixed $expectedResult
      */
-    public function testADDRESS($expectedResult, ...$args): void
+    public function testADDRESS(mixed $expectedResult, mixed ...$args): void
     {
         $result = LookupRef\Address::cell(...$args);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AllSetupTeardown.php
index 52f561e111..46947d7d1f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/AllSetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -51,20 +53,14 @@ protected static function setGnumeric(): void
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_GNUMERIC);
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    protected function mightHaveException($expectedResult): void
+    protected function mightHaveException(mixed $expectedResult): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(CalcException::class);
         }
     }
 
-    /**
-     * @param mixed $value
-     */
-    protected function setCell(string $cell, $value): void
+    protected function setCell(string $cell, mixed $value): void
     {
         if ($value !== null) {
             if (is_string($value) && is_numeric($value)) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ChooseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ChooseTest.php
index 76421f2527..7a495a5ca3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ChooseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ChooseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,10 +12,8 @@ class ChooseTest extends TestCase
 {
     /**
      * @dataProvider providerCHOOSE
-     *
-     * @param mixed $expectedResult
      */
-    public function testCHOOSE($expectedResult, ...$args): void
+    public function testCHOOSE(mixed $expectedResult, mixed ...$args): void
     {
         $result = LookupRef\Selection::choose(...$args);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnOnSpreadsheetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnOnSpreadsheetTest.php
index 6ba99f016c..de7a6cc229 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnOnSpreadsheetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnOnSpreadsheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
@@ -8,11 +10,8 @@ class ColumnOnSpreadsheetTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOLUMNonSpreadsheet
-     *
-     * @param mixed $expectedResult
-     * @param string $cellReference
      */
-    public function testColumnOnSpreadsheet($expectedResult, $cellReference = 'omitted'): void
+    public function testColumnOnSpreadsheet(mixed $expectedResult, string $cellReference = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnTest.php
index 75e7a4ed21..9b007b0a93 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\LookupRef;
@@ -8,11 +10,8 @@ class ColumnTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOLUMN
-     *
-     * @param mixed $expectedResult
-     * @param null|array|string $cellReference
      */
-    public function testCOLUMN($expectedResult, $cellReference = null): void
+    public function testCOLUMN(mixed $expectedResult, null|array|string $cellReference = null): void
     {
         $result = LookupRef\RowColumnInformation::COLUMN($cellReference);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsOnSpreadsheetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsOnSpreadsheetTest.php
index 2ff070c6f6..76c866e5ca 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsOnSpreadsheetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsOnSpreadsheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
@@ -8,11 +10,8 @@ class ColumnsOnSpreadsheetTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOLUMNSonSpreadsheet
-     *
-     * @param mixed $expectedResult
-     * @param string $cellReference
      */
-    public function testColumnsOnSpreadsheet($expectedResult, $cellReference = 'omitted'): void
+    public function testColumnsOnSpreadsheet(mixed $expectedResult, string $cellReference = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsTest.php
index c3bdad29e6..641119a9d7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/ColumnsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,11 +12,8 @@ class ColumnsTest extends TestCase
 {
     /**
      * @dataProvider providerCOLUMNS
-     *
-     * @param mixed $expectedResult
-     * @param null|array|string $arg
      */
-    public function testCOLUMNS($expectedResult, $arg): void
+    public function testCOLUMNS(mixed $expectedResult, null|array|string $arg): void
     {
         $result = LookupRef\RowColumnInformation::COLUMNS($arg);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FilterTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FilterTest.php
index 5a584c4645..ad0f4f0ee6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FilterTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FormulaTextTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FormulaTextTest.php
index e024e04306..23a52cab33 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FormulaTextTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/FormulaTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\LookupRef\Formula;
@@ -10,11 +12,9 @@
 class FormulaTextTest extends AllSetupTeardown
 {
     /**
-     * @param mixed $value
-     *
      * @dataProvider providerFormulaText
      */
-    public function testFormulaText(string $expectedResult, $value): void
+    public function testFormulaText(string $expectedResult, mixed $value): void
     {
         $sheet = $this->getSheet();
         $reference = 'A1';
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HLookupTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HLookupTest.php
index 57c7caf507..682a12e021 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HLookupTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HLookupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,12 +14,8 @@ class HLookupTest extends TestCase
 {
     /**
      * @dataProvider providerHLOOKUP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $lookup
-     * @param mixed $rowIndex
      */
-    public function testHLOOKUP($expectedResult, $lookup, array $values, $rowIndex, ?bool $rangeLookup = null): void
+    public function testHLOOKUP(mixed $expectedResult, mixed $lookup, array $values, mixed $rowIndex, ?bool $rangeLookup = null): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HyperlinkTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HyperlinkTest.php
index 6ebd05384a..5eaf7d35eb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HyperlinkTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/HyperlinkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
@@ -12,10 +14,8 @@ class HyperlinkTest extends AllSetupTeardown
 
     /**
      * @dataProvider providerHYPERLINK
-     *
-     * @param array|string $expectedResult
      */
-    public function testHYPERLINK($expectedResult, ?string $linkUrl, ?string $description): void
+    public function testHYPERLINK(array|string $expectedResult, ?string $linkUrl, ?string $description): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -42,10 +42,8 @@ public function testHYPERLINK($expectedResult, ?string $linkUrl, ?string $descri
 
     /**
      * @dataProvider providerHYPERLINK
-     *
-     * @param array|string $expectedResult
      */
-    public function testHYPERLINKcellRef($expectedResult, ?string $linkUrl, ?string $description): void
+    public function testHYPERLINKcellRef(array|string $expectedResult, ?string $linkUrl, ?string $description): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexOnSpreadsheetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexOnSpreadsheetTest.php
index abae76d186..e893fc7f3f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexOnSpreadsheetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexOnSpreadsheetTest.php
@@ -1,17 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 class IndexOnSpreadsheetTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerINDEXonSpreadsheet
-     *
-     * @param mixed $expectedResult
-     * @param null|int|string $rowNum
-     * @param null|int|string $colNum
      */
-    public function testIndexOnSpreadsheet($expectedResult, array $matrix, $rowNum = null, $colNum = null): void
+    public function testIndexOnSpreadsheet(mixed $expectedResult, array $matrix, null|int|string $rowNum = null, null|int|string $colNum = null): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexTest.php
index 6d2ee6bad5..9b3f5de2ec 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,13 +13,8 @@ class IndexTest extends TestCase
 {
     /**
      * @dataProvider providerINDEX
-     *
-     * @param mixed $expectedResult
-     * @param mixed $matrix
-     * @param mixed $rowNum
-     * @param mixed $colNum
      */
-    public function testINDEX($expectedResult, $matrix, $rowNum = null, $colNum = null): void
+    public function testINDEX(mixed $expectedResult, mixed $matrix, mixed $rowNum = null, mixed $colNum = null): void
     {
         if ($rowNum === null) {
             $result = Matrix::index($matrix);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectInternationalTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectInternationalTest.php
index 881fb2f952..1cfcfc603b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectInternationalTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectInternationalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -7,8 +9,7 @@
 
 class IndirectInternationalTest extends AllSetupTeardown
 {
-    /** @var string */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectTest.php
index 8f0727e0c2..3ea20cac3a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/IndirectTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\NamedFormula;
@@ -10,12 +12,8 @@ class IndirectTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerINDIRECT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $cellReference
-     * @param mixed $a1
      */
-    public function testINDIRECT($expectedResult, $cellReference = 'omitted', $a1 = 'omitted'): void
+    public function testINDIRECT(mixed $expectedResult, mixed $cellReference = 'omitted', mixed $a1 = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -135,11 +133,9 @@ public function testDeprecatedCall(): void
     }
 
     /**
-     * @param null|int|string $expectedResult
-     *
      * @dataProvider providerRelative
      */
-    public function testR1C1Relative($expectedResult, string $address): void
+    public function testR1C1Relative(string|int|null $expectedResult, string $address): void
     {
         $sheet = $this->getSheet();
         $sheet->fromArray([
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/LookupTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/LookupTest.php
index fbc593f107..7194fe3806 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/LookupTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/LookupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,10 +13,8 @@ class LookupTest extends TestCase
 {
     /**
      * @dataProvider providerLOOKUP
-     *
-     * @param mixed $expectedResult
      */
-    public function testLOOKUP($expectedResult, ...$args): void
+    public function testLOOKUP(mixed $expectedResult, mixed ...$args): void
     {
         $result = LookupRef\Lookup::lookup(...$args);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatchTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatchTest.php
index 3ab4eaf567..6a1c809f1e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatchTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatchTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class MatchTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMATCH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $input
-     * @param mixed $type
      */
-    public function testMATCH($expectedResult, $input, array $array, $type = null): void
+    public function testMATCH(mixed $expectedResult, mixed $input, array $array, mixed $type = null): void
     {
         if (is_array($expectedResult)) {
             $expectedResult = $expectedResult[0];
@@ -43,12 +41,8 @@ public function testMATCH($expectedResult, $input, array $array, $type = null):
 
     /**
      * @dataProvider providerMATCH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $input
-     * @param mixed $type
      */
-    public function testMATCHLibre($expectedResult, $input, array $array, $type = null): void
+    public function testMATCHLibre(mixed $expectedResult, mixed $input, array $array, mixed $type = null): void
     {
         $this->setOpenOffice();
         if (is_array($expectedResult)) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatrixHelperFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatrixHelperFunctionsTest.php
index 60952babdd..62e3b03578 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatrixHelperFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MatrixHelperFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\LookupRef\Matrix;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MovedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MovedFunctionsTest.php
index 0f732306ca..b96ad342cf 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MovedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/MovedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/OffsetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/OffsetTest.php
index 781bf9dbe5..2bf7f67bc6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/OffsetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/OffsetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\LookupRef;
@@ -9,11 +11,8 @@ class OffsetTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerOFFSET
-     *
-     * @param mixed $expectedResult
-     * @param null|string $cellReference
      */
-    public function testOFFSET($expectedResult, $cellReference = null): void
+    public function testOFFSET(mixed $expectedResult, null|string $cellReference = null): void
     {
         $result = LookupRef\Offset::OFFSET($cellReference);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowOnSpreadsheetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowOnSpreadsheetTest.php
index c7101674b5..53fdbf0877 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowOnSpreadsheetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowOnSpreadsheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
@@ -8,11 +10,8 @@ class RowOnSpreadsheetTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerROWonSpreadsheet
-     *
-     * @param mixed $expectedResult
-     * @param string $cellReference
      */
-    public function testRowOnSpreadsheet($expectedResult, $cellReference = 'omitted'): void
+    public function testRowOnSpreadsheet(mixed $expectedResult, string $cellReference = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowTest.php
index 48d6cf08c3..fbc4c12d6b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\LookupRef;
@@ -8,11 +10,8 @@ class RowTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerROW
-     *
-     * @param mixed $expectedResult
-     * @param null|array|string $cellReference
      */
-    public function testROW($expectedResult, $cellReference = null): void
+    public function testROW(mixed $expectedResult, null|array|string $cellReference = null): void
     {
         $result = LookupRef\RowColumnInformation::ROW($cellReference);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsOnSpreadsheetTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsOnSpreadsheetTest.php
index 36dec5111c..5d21d9fc7e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsOnSpreadsheetTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsOnSpreadsheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
@@ -8,11 +10,8 @@ class RowsOnSpreadsheetTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerROWSonSpreadsheet
-     *
-     * @param mixed $expectedResult
-     * @param string $cellReference
      */
-    public function testRowsOnSpreadsheet($expectedResult, $cellReference = 'omitted'): void
+    public function testRowsOnSpreadsheet(mixed $expectedResult, string $cellReference = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsTest.php
index 74dcb9c6b8..11781aabc5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/RowsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,11 +12,8 @@ class RowsTest extends TestCase
 {
     /**
      * @dataProvider providerROWS
-     *
-     * @param mixed $expectedResult
-     * @param null|array|string $arg
      */
-    public function testROWS($expectedResult, $arg): void
+    public function testROWS(mixed $expectedResult, null|array|string $arg): void
     {
         $result = LookupRef\RowColumnInformation::ROWS($arg);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php
index a2eb006d5b..99e0a6e45d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortByTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
@@ -18,11 +20,8 @@ public function testSortOnScalar(): void
 
     /**
      * @dataProvider providerSortWithScalarArgumentErrorReturns
-     *
-     * @param mixed $sortIndex
-     * @param mixed $sortOrder
      */
-    public function testSortByWithArgumentErrorReturns($sortIndex, $sortOrder = 1): void
+    public function testSortByWithArgumentErrorReturns(mixed $sortIndex, mixed $sortOrder = 1): void
     {
         $value = [[1, 2], [3, 4], [5, 6]];
 
@@ -45,7 +44,7 @@ public static function providerSortWithScalarArgumentErrorReturns(): array
     /**
      * @dataProvider providerSortByRow
      */
-    public function testSortByRow(array $expectedResult, array $matrix, ...$args): void
+    public function testSortByRow(array $expectedResult, array $matrix, mixed ...$args): void
     {
         $result = Sort::sortBy($matrix, ...$args);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php
index 3145cfd3e7..8334c20bff 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/SortTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
@@ -18,11 +20,8 @@ public function testSortOnScalar(): void
 
     /**
      * @dataProvider providerSortWithScalarArgumentErrorReturns
-     *
-     * @param mixed $sortIndex
-     * @param mixed $sortOrder
      */
-    public function testSortWithScalarArgumentErrorReturns($sortIndex, $sortOrder = 1): void
+    public function testSortWithScalarArgumentErrorReturns(mixed $sortIndex, mixed $sortOrder = 1): void
     {
         $value = [[1, 2], [3, 4], [5, 6]];
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/TransposeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/TransposeTest.php
index acb9e110fe..1892695698 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/TransposeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/TransposeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -15,11 +17,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerTRANSPOSE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $matrix
      */
-    public function testTRANSPOSE($expectedResult, $matrix): void
+    public function testTRANSPOSE(mixed $expectedResult, mixed $matrix): void
     {
         $result = LookupRef\Matrix::transpose($matrix);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/UniqueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/UniqueTest.php
index 44c071d2d5..718fe2b8b0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/UniqueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/UniqueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/VLookupTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/VLookupTest.php
index 54e350d3cd..b898dbd5f6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/VLookupTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/LookupRef/VLookupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\LookupRef;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,13 +12,8 @@ class VLookupTest extends TestCase
 {
     /**
      * @dataProvider providerVLOOKUP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
-     * @param mixed $table
-     * @param mixed $index
      */
-    public function testVLOOKUP($expectedResult, $value, $table, $index, ?bool $lookup = null): void
+    public function testVLOOKUP(mixed $expectedResult, mixed $value, mixed $table, mixed $index, ?bool $lookup = null): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AbsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AbsTest.php
index 411131713e..e16a05d77f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AbsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AbsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class AbsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAbs
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testAbs($expectedResult, $number = 'omitted'): void
+    public function testAbs(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $sheet = $this->getSheet();
         $this->mightHaveException($expectedResult);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcosTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcosTest.php
index e945801787..8ba2e2a3a9 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcosTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcosTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class AcosTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAcos
-     *
-     * @param mixed $expectedResult
      */
-    public function testAcos($expectedResult, string $formula): void
+    public function testAcos(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcoshTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcoshTest.php
index b4bbacf0b3..98ca3353cc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcoshTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcoshTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class AcoshTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAcosh
-     *
-     * @param mixed $expectedResult
      */
-    public function testAcosh($expectedResult, string $formula): void
+    public function testAcosh(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcotTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcotTest.php
index 326ec400d3..eabdd51154 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcotTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcotTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class AcotTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerACOT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testACOT($expectedResult, $number): void
+    public function testACOT(mixed $expectedResult, mixed $number): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcothTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcothTest.php
index def904eac3..3935a32e98 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcothTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AcothTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class AcothTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerACOTH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testACOTH($expectedResult, $number): void
+    public function testACOTH(mixed $expectedResult, mixed $number): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AllSetupTeardown.php
index f54ecaad9e..a73de31c0f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AllSetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -11,10 +13,7 @@
 
 class AllSetupTeardown extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     /**
      * @var ?Spreadsheet
@@ -51,20 +50,14 @@ protected static function setGnumeric(): void
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_GNUMERIC);
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    protected function mightHaveException($expectedResult): void
+    protected function mightHaveException(mixed $expectedResult): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(CalcException::class);
         }
     }
 
-    /**
-     * @param mixed $value
-     */
-    protected function setCell(string $cell, $value): void
+    protected function setCell(string $cell, mixed $value): void
     {
         if ($value !== null) {
             if (is_string($value) && is_numeric($value)) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ArabicTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ArabicTest.php
index 2c80a07e4a..d5fd394a73 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ArabicTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ArabicTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class ArabicTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerARABIC
-     *
-     * @param mixed $expectedResult
-     * @param string $romanNumeral
      */
-    public function testARABIC($expectedResult, $romanNumeral): void
+    public function testARABIC(mixed $expectedResult, string $romanNumeral): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinTest.php
index 98f66957d3..6024504c4c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class AsinTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAsin
-     *
-     * @param mixed $expectedResult
      */
-    public function testAsin($expectedResult, string $formula): void
+    public function testAsin(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinhTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinhTest.php
index 53b9777aa6..019ffb5507 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinhTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AsinhTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class AsinhTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAsinh
-     *
-     * @param mixed $expectedResult
      */
-    public function testAsinh($expectedResult, string $formula): void
+    public function testAsinh(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Atan2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Atan2Test.php
index 2fb7c0f5c4..be37fdd241 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Atan2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Atan2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class Atan2Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerATAN2
-     *
-     * @param mixed $expectedResult
      */
-    public function testATAN2($expectedResult, string $formula): void
+    public function testATAN2(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanTest.php
index 3de5f1ab64..d4156d6c2e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class AtanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAtan
-     *
-     * @param mixed $expectedResult
      */
-    public function testAtan($expectedResult, string $formula): void
+    public function testAtan(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanhTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanhTest.php
index 3e7cdb2ab6..0433535e3e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanhTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/AtanhTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class AtanhTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAtanh
-     *
-     * @param mixed $expectedResult
      */
-    public function testAtanh($expectedResult, string $formula): void
+    public function testAtanh(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/BaseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/BaseTest.php
index 90360305f3..77b661c669 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/BaseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/BaseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,13 +10,8 @@ class BaseTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBASE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $arg1
-     * @param mixed $arg2
-     * @param mixed $arg3
      */
-    public function testBASE($expectedResult, $arg1 = 'omitted', $arg2 = 'omitted', $arg3 = 'omitted'): void
+    public function testBASE(mixed $expectedResult, mixed $arg1 = 'omitted', mixed $arg2 = 'omitted', mixed $arg3 = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingMathTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingMathTest.php
index 1ae3c83e9a..384600d5b5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingMathTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingMathTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CeilingMathTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCEILINGMATH
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testCEILINGMATH($expectedResult, $formula): void
+    public function testCEILINGMATH(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingPreciseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingPreciseTest.php
index 00bb6e1b1e..d6e60e5294 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingPreciseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingPreciseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CeilingPreciseTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFLOORPRECISE
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testCEILINGPRECISE($expectedResult, $formula): void
+    public function testCEILINGPRECISE(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingTest.php
index c12040cc8a..ba246a03e3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CeilingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CeilingTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCEILING
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testCEILING($expectedResult, $formula): void
+    public function testCEILING(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinATest.php
index 260d6d20ea..bc3d41ba81 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinATest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class CombinATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOMBINA
-     *
-     * @param mixed $expectedResult
-     * @param mixed $numObjs
-     * @param mixed $numInSet
      */
-    public function testCOMBINA($expectedResult, $numObjs, $numInSet): void
+    public function testCOMBINA(mixed $expectedResult, mixed $numObjs, mixed $numInSet): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinTest.php
index f7fcfed741..6c4cdfa26c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CombinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class CombinTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOMBIN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $numObjs
-     * @param mixed $numInSet
      */
-    public function testCOMBIN($expectedResult, $numObjs, $numInSet): void
+    public function testCOMBIN(mixed $expectedResult, mixed $numObjs, mixed $numInSet): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CosTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CosTest.php
index 4f07320173..0f5513d2da 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CosTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CosTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class CosTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCos
-     *
-     * @param mixed $expectedResult
      */
-    public function testCos($expectedResult, string $formula): void
+    public function testCos(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CoshTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CoshTest.php
index caabfdd761..0239c1ee6f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CoshTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CoshTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class CoshTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCosh
-     *
-     * @param mixed $expectedResult
      */
-    public function testCosh($expectedResult, string $formula): void
+    public function testCosh(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CotTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CotTest.php
index 5fd56b0b11..d7c71af594 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CotTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CotTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CotTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $angle
      */
-    public function testCOT($expectedResult, $angle): void
+    public function testCOT(mixed $expectedResult, mixed $angle): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CothTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CothTest.php
index a14f9b40fc..1527ef764b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CothTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CothTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CothTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOTH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $angle
      */
-    public function testCOTH($expectedResult, $angle): void
+    public function testCOTH(mixed $expectedResult, mixed $angle): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CscTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CscTest.php
index f64cef3a55..2b64c71a8a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CscTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CscTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CscTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCSC
-     *
-     * @param mixed $expectedResult
-     * @param mixed $angle
      */
-    public function testCSC($expectedResult, $angle): void
+    public function testCSC(mixed $expectedResult, mixed $angle): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CschTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CschTest.php
index b6d0297666..9f2bf9050b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CschTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/CschTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CschTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCSCH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $angle
      */
-    public function testCSCH($expectedResult, $angle): void
+    public function testCSCH(mixed $expectedResult, mixed $angle): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/DegreesTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/DegreesTest.php
index 42bdc17029..14d3d72bd4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/DegreesTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/DegreesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class DegreesTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDEGREES
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testDegrees($expectedResult, $number = 'omitted'): void
+    public function testDegrees(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $sheet = $this->getSheet();
         $this->mightHaveException($expectedResult);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/EvenTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/EvenTest.php
index 275c8f4ef5..88166169e7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/EvenTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/EvenTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class EvenTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerEVEN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testEVEN($expectedResult, $value): void
+    public function testEVEN(mixed $expectedResult, mixed $value): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ExpTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ExpTest.php
index 38c9e88abd..7af6b3b095 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ExpTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ExpTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class ExpTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerEXP
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testEXP($expectedResult, $number = 'omitted'): void
+    public function testEXP(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactDoubleTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactDoubleTest.php
index 441579ba2c..e405c5d0f5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactDoubleTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactDoubleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class FactDoubleTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFACTDOUBLE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testFACTDOUBLE($expectedResult, $value): void
+    public function testFACTDOUBLE(mixed $expectedResult, mixed $value): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactTest.php
index 69cefc4d4a..1b1dbdb5c3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FactTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,11 +12,8 @@ class FactTest extends AllSetupTeardown
 
     /**
      * @dataProvider providerFACT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $arg1
      */
-    public function testFACT($expectedResult, $arg1): void
+    public function testFACT(mixed $expectedResult, mixed $arg1): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -37,11 +36,8 @@ public static function providerFACT(): array
 
     /**
      * @dataProvider providerFACTGnumeric
-     *
-     * @param mixed $expectedResult
-     * @param mixed $arg1
      */
-    public function testFACTGnumeric($expectedResult, $arg1): void
+    public function testFACTGnumeric(mixed $expectedResult, mixed $arg1): void
     {
         $this->mightHaveException($expectedResult);
         self::setGnumeric();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorMathTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorMathTest.php
index e37023e921..f91076a239 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorMathTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorMathTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class FloorMathTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFLOORMATH
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testFLOORMATH($expectedResult, $formula): void
+    public function testFLOORMATH(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorPreciseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorPreciseTest.php
index 8573af868f..3a43822e94 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorPreciseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorPreciseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class FloorPreciseTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFLOORPRECISE
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testFLOORPRECISE($expectedResult, $formula): void
+    public function testFLOORPRECISE(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorTest.php
index f4d5529586..3d56fb3282 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/FloorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class FloorTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFLOOR
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testFLOOR($expectedResult, $formula): void
+    public function testFLOOR(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/GcdTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/GcdTest.php
index 01f2b21f06..e7684ba14a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/GcdTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/GcdTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class GcdTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGCD
-     *
-     * @param mixed $expectedResult
      */
-    public function testGCD($expectedResult, ...$args): void
+    public function testGCD(mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/IntTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/IntTest.php
index a861ac80ee..7f551e3430 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/IntTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/IntTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class IntTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerINT
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testINT($expectedResult, $formula): void
+    public function testINT(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LcmTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LcmTest.php
index a798ce2a12..13d3b99402 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LcmTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LcmTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class LcmTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLCM
-     *
-     * @param mixed $expectedResult
      */
-    public function testLCM($expectedResult, ...$args): void
+    public function testLCM(mixed $expectedResult, mixed ...$args): void
     {
         $sheet = $this->getSheet();
         $row = 0;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LnTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LnTest.php
index 49305d1434..ca7eb78e86 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LnTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class LnTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testLN($expectedResult, $number = 'omitted'): void
+    public function testLN(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Log10Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Log10Test.php
index 4424565470..63ff4e9521 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Log10Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/Log10Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class Log10Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLOG10
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testLOG10($expectedResult, $number = 'omitted'): void
+    public function testLOG10(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LogTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LogTest.php
index f4baf1b725..69cd275be2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LogTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/LogTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class LogTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLOG
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
-     * @param mixed $base
      */
-    public function testLOG($expectedResult, $number = 'omitted', $base = 'omitted'): void
+    public function testLOG(mixed $expectedResult, mixed $number = 'omitted', mixed $base = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MInverseTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MInverseTest.php
index b704bc5f89..63c118572f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MInverseTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MInverseTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\MathTrig;
@@ -8,10 +10,8 @@ class MInverseTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMINVERSE
-     *
-     * @param mixed $expectedResult
      */
-    public function testMINVERSE($expectedResult, array $args): void
+    public function testMINVERSE(mixed $expectedResult, array $args): void
     {
         $result = MathTrig\MatrixFunctions::inverse($args);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-8);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MMultTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MMultTest.php
index eb7ed81da4..86ee26fd9c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MMultTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MMultTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\MathTrig;
@@ -8,10 +10,8 @@ class MMultTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMMULT
-     *
-     * @param mixed $expectedResult
      */
-    public function testMMULT($expectedResult, ...$args): void
+    public function testMMULT(mixed $expectedResult, mixed ...$args): void
     {
         $result = MathTrig\MatrixFunctions::multiply(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-8);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MRoundTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MRoundTest.php
index 34894c81ad..520f6d50ec 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MRoundTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MRoundTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class MRoundTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMROUND
-     *
-     * @param mixed $expectedResult
-     * @param mixed $formula
      */
-    public function testMROUND($expectedResult, $formula): void
+    public function testMROUND(mixed $expectedResult, mixed $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MUnitTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MUnitTest.php
index 9ac68ee5e9..5d1abe126f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MUnitTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MUnitTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\MathTrig\MatrixFunctions;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MdeTermTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MdeTermTest.php
index 01c6899b7e..8928f32c7c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MdeTermTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MdeTermTest.php
@@ -1,16 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class MdeTermTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMDETERM
-     *
-     * @param mixed $expectedResult
-     * @param mixed $matrix expect a matrix
      */
-    public function testMDETERM2($expectedResult, $matrix): void
+    public function testMDETERM2(mixed $expectedResult, mixed $matrix): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ModTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ModTest.php
index f1fc1ea255..f33b886509 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ModTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ModTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class ModTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMOD
-     *
-     * @param mixed $expectedResult
-     * @param mixed $dividend
-     * @param mixed $divisor
      */
-    public function testMOD($expectedResult, $dividend = 'omitted', $divisor = 'omitted'): void
+    public function testMOD(mixed $expectedResult, mixed $dividend = 'omitted', mixed $divisor = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MovedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MovedFunctionsTest.php
index 646fd634b2..91e0a92f87 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MovedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MovedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\MathTrig;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MultinomialTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MultinomialTest.php
index ffb66ef320..ce189b44ef 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MultinomialTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/MultinomialTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class MultinomialTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMULTINOMIAL
-     *
-     * @param mixed $expectedResult
      */
-    public function testMULTINOMIAL($expectedResult, ...$args): void
+    public function testMULTINOMIAL(mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/OddTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/OddTest.php
index 7b3a4ab859..de4522368a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/OddTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/OddTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class OddTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerODD
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testODD($expectedResult, $value): void
+    public function testODD(mixed $expectedResult, mixed $value): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/PowerTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/PowerTest.php
index db3411f522..0bf42f09a8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/PowerTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/PowerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class PowerTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPOWER
-     *
-     * @param mixed $expectedResult
-     * @param mixed $base
-     * @param mixed $exponent
      */
-    public function testPOWER($expectedResult, $base = 'omitted', $exponent = 'omitted'): void
+    public function testPOWER(mixed $expectedResult, mixed $base = 'omitted', mixed $exponent = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ProductTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ProductTest.php
index fb64446330..7b4bc296e3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ProductTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/ProductTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class ProductTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPRODUCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testPRODUCT($expectedResult, ...$args): void
+    public function testPRODUCT(mixed $expectedResult, mixed ...$args): void
     {
         $sheet = $this->getSheet();
         $row = 0;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/QuotientTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/QuotientTest.php
index 90878696b0..84c2856be4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/QuotientTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/QuotientTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class QuotientTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerQUOTIENT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $arg1
-     * @param mixed $arg2
      */
-    public function testQUOTIENT($expectedResult, $arg1 = 'omitted', $arg2 = 'omitted'): void
+    public function testQUOTIENT(mixed $expectedResult, mixed $arg1 = 'omitted', mixed $arg2 = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RadiansTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RadiansTest.php
index d39c3615ba..fb3c784eb1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RadiansTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RadiansTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class RadiansTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRADIANS
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testRADIANS($expectedResult, $number = 'omitted'): void
+    public function testRADIANS(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $sheet = $this->getSheet();
         $this->mightHaveException($expectedResult);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandArrayTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandArrayTest.php
index 6fffb31c77..3b5f730258 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandArrayTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandArrayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandBetweenTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandBetweenTest.php
index 7e8cc327fe..059723616e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandBetweenTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandBetweenTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class RandBetweenTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRANDBETWEEN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $min
-     * @param mixed $max
      */
-    public function testRANDBETWEEN($expectedResult, $min = 'omitted', $max = 'omitted'): void
+    public function testRANDBETWEEN(mixed $expectedResult, mixed $min = 'omitted', mixed $max = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandTest.php
index 989c4883b4..f1cd7cc70b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RandTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class RandTest extends AllSetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RomanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RomanTest.php
index 5b6de348e4..1e536a11ae 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RomanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RomanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class RomanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerROMAN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $formula
      */
-    public function testROMAN($expectedResult, $formula): void
+    public function testROMAN(mixed $expectedResult, mixed $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundDownTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundDownTest.php
index 1d9d2b6027..b65da3627c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundDownTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundDownTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class RoundDownTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRoundDown
-     *
-     * @param mixed $expectedResult
-     * @param mixed $formula
      */
-    public function testRoundDown($expectedResult, $formula): void
+    public function testRoundDown(mixed $expectedResult, mixed $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundTest.php
index dbea38efc2..b9d776242f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class RoundTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRound
-     *
-     * @param mixed $expectedResult
-     * @param mixed $formula
      */
-    public function testRound($expectedResult, $formula): void
+    public function testRound(mixed $expectedResult, mixed $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundUpTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundUpTest.php
index f360c2ee44..5ad00d36ea 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundUpTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/RoundUpTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class RoundUpTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRoundUp
-     *
-     * @param mixed $expectedResult
-     * @param mixed $formula
      */
-    public function testRoundUp($expectedResult, $formula): void
+    public function testRoundUp(mixed $expectedResult, mixed $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SecTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SecTest.php
index 4cd608c7ec..4485b566f0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SecTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SecTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class SecTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSEC
-     *
-     * @param mixed $expectedResult
-     * @param mixed $angle
      */
-    public function testSEC($expectedResult, $angle): void
+    public function testSEC(mixed $expectedResult, mixed $angle): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SechTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SechTest.php
index 9260179419..7605f95fc5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SechTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SechTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class SechTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSECH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $angle
      */
-    public function testSECH($expectedResult, $angle): void
+    public function testSECH(mixed $expectedResult, mixed $angle): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SequenceTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SequenceTest.php
index a3cd1c37a6..4db230ece0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SequenceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SequenceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\MathTrig\MatrixFunctions;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SeriesSumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SeriesSumTest.php
index 4a6d4411b1..8608f91c87 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SeriesSumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SeriesSumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -9,13 +11,8 @@ class SeriesSumTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSERIESSUM
-     *
-     * @param mixed $expectedResult
-     * @param mixed $arg1
-     * @param mixed $arg2
-     * @param mixed $arg3
      */
-    public function testSERIESSUM($expectedResult, $arg1, $arg2, $arg3, ...$args): void
+    public function testSERIESSUM(mixed $expectedResult, mixed $arg1, mixed $arg2, mixed $arg3, mixed ...$args): void
     {
         $sheet = $this->getSheet();
         if ($arg1 !== null) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SignTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SignTest.php
index a62804681d..436d0fe02b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SignTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SignTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class SignTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSIGN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testSIGN($expectedResult, $value): void
+    public function testSIGN(mixed $expectedResult, mixed $value): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinTest.php
index 62f0355916..83bc295f80 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class SinTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSin
-     *
-     * @param mixed $expectedResult
      */
-    public function testSin($expectedResult, string $formula): void
+    public function testSin(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinhTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinhTest.php
index 045d32768e..0ad727757e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinhTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SinhTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class SinhTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCosh
-     *
-     * @param mixed $expectedResult
      */
-    public function testSinh($expectedResult, string $formula): void
+    public function testSinh(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtPiTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtPiTest.php
index b04b512f3d..e6a1e783d3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtPiTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtPiTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class SqrtPiTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSQRTPI
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testSQRTPI($expectedResult, $number): void
+    public function testSQRTPI(mixed $expectedResult, mixed $number): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtTest.php
index 6dc39d6cc1..4bd348ffc7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SqrtTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class SqrtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSQRT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
      */
-    public function testSQRT($expectedResult, $number = 'omitted'): void
+    public function testSQRT(mixed $expectedResult, mixed $number = 'omitted'): void
     {
         $sheet = $this->getSheet();
         $this->mightHaveException($expectedResult);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SubTotalTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SubTotalTest.php
index 7ac398c414..b93b7f2609 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SubTotalTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SubTotalTest.php
@@ -1,16 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class SubTotalTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUBTOTAL
-     *
-     * @param mixed $expectedResult
-     * @param mixed $type expect an integer
      */
-    public function testSubtotal($expectedResult, $type): void
+    public function testSubtotal(mixed $expectedResult, mixed $type): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -29,11 +28,8 @@ public static function providerSUBTOTAL(): array
 
     /**
      * @dataProvider providerSUBTOTAL
-     *
-     * @param mixed $expectedResult
-     * @param mixed $type expect an integer
      */
-    public function testSubtotalColumnHidden($expectedResult, $type): void
+    public function testSubtotalColumnHidden(mixed $expectedResult, mixed $type): void
     {
         // Hidden columns don't affect calculation, only hidden rows
         $this->mightHaveException($expectedResult);
@@ -66,11 +62,8 @@ public function testSubtotalColumnHidden($expectedResult, $type): void
 
     /**
      * @dataProvider providerSUBTOTALHIDDEN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $type expect an integer
      */
-    public function testSubtotalRowHidden($expectedResult, $type): void
+    public function testSubtotalRowHidden(mixed $expectedResult, mixed $type): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfTest.php
index a42153ad44..1f61aa8632 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfTest.php
@@ -1,16 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class SumIfTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMIF
-     *
-     * @param mixed $expectedResult
-     * @param mixed $condition
      */
-    public function testSUMIF2($expectedResult, array $array1, $condition, ?array $array2 = null): void
+    public function testSUMIF2(mixed $expectedResult, array $array1, mixed $condition, ?array $array2 = null): void
     {
         $this->mightHaveException($expectedResult);
         if ($expectedResult === 'incomplete') {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfsTest.php
index aecb777711..eca29781f2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumIfsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -8,10 +10,8 @@ class SumIfsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMIFS
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMIFS($expectedResult, ...$args): void
+    public function testSUMIFS(mixed $expectedResult, mixed ...$args): void
     {
         $result = Statistical\Conditional::SUMIFS(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumProductTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumProductTest.php
index dd7dcc852d..2158894b94 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumProductTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumProductTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -8,10 +10,8 @@ class SumProductTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMPRODUCT
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMPRODUCT($expectedResult, ...$args): void
+    public function testSUMPRODUCT(mixed $expectedResult, mixed ...$args): void
     {
         $sheet = $this->getSheet();
         $row = 0;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumSqTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumSqTest.php
index 2b8ed93e8c..41b3e4c61f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumSqTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumSqTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 class SumSqTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMSQ
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMSQ($expectedResult, ...$args): void
+    public function testSUMSQ(mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $maxRow = 0;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumTest.php
index e51662f985..5c9bd238d8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -8,10 +10,8 @@ class SumTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUM
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUM($expectedResult, ...$args): void
+    public function testSUM(mixed $expectedResult, mixed ...$args): void
     {
         $sheet = $this->getSheet();
         $row = 0;
@@ -31,10 +31,8 @@ public static function providerSUM(): array
 
     /**
      * @dataProvider providerSUMLiterals
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMLiterals($expectedResult, string $args): void
+    public function testSUMLiterals(mixed $expectedResult, string $args): void
     {
         $sheet = $this->getSheet();
         $sheet->getCell('B1')->setValue("=SUM($args)");
@@ -49,10 +47,8 @@ public static function providerSUMLiterals(): array
 
     /**
      * @dataProvider providerSUMWITHINDEXMATCH
-     *
-     * @param mixed $expectedResult
      */
-    public function testSumWithIndexMatch($expectedResult, string $formula): void
+    public function testSumWithIndexMatch(mixed $expectedResult, string $formula): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet1 = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2MY2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2MY2Test.php
index 2872f734d1..c7d1bf8c2b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2MY2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2MY2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -8,10 +10,8 @@ class SumX2MY2Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMX2MY2
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMX2MY2($expectedResult, array $matrixData1, array $matrixData2): void
+    public function testSUMX2MY2(mixed $expectedResult, array $matrixData1, array $matrixData2): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2PY2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2PY2Test.php
index 08f30dfb3c..b75ea02dfc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2PY2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumX2PY2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -8,10 +10,8 @@ class SumX2PY2Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMX2PY2
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMX2PY2($expectedResult, array $matrixData1, array $matrixData2): void
+    public function testSUMX2PY2(mixed $expectedResult, array $matrixData1, array $matrixData2): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumXMY2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumXMY2Test.php
index 3e5c31dc84..4cce0ada0e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumXMY2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/SumXMY2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -8,10 +10,8 @@ class SumXMY2Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUMXMY2
-     *
-     * @param mixed $expectedResult
      */
-    public function testSUMXMY2($expectedResult, array $matrixData1, array $matrixData2): void
+    public function testSUMXMY2(mixed $expectedResult, array $matrixData1, array $matrixData2): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanTest.php
index f20aa5c24f..c21d451a1b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class TanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTan
-     *
-     * @param mixed $expectedResult
      */
-    public function testTan($expectedResult, string $formula): void
+    public function testTan(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanhTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanhTest.php
index e2c4f56114..8de5d6803e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanhTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TanhTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class TanhTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTanh
-     *
-     * @param mixed $expectedResult
      */
-    public function testTanh($expectedResult, string $formula): void
+    public function testTanh(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TruncTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TruncTest.php
index 445e3ae94b..beaf0a8313 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TruncTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/MathTrig/TruncTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\MathTrig;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class TruncTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTRUNC
-     *
-     * @param mixed $expectedResult
-     * @param string $formula
      */
-    public function testTRUNC($expectedResult, $formula): void
+    public function testTRUNC(mixed $expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AllSetupTeardown.php
index f5186c6318..da8038189a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AllSetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -11,10 +13,7 @@
 
 class AllSetupTeardown extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     /**
      * @var ?Spreadsheet
@@ -51,20 +50,14 @@ protected static function setGnumeric(): void
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_GNUMERIC);
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    protected function mightHaveException($expectedResult): void
+    protected function mightHaveException(mixed $expectedResult): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(CalcException::class);
         }
     }
 
-    /**
-     * @param mixed $value
-     */
-    protected function setCell(string $cell, $value): void
+    protected function setCell(string $cell, mixed $value): void
     {
         if ($value !== null) {
             if (is_string($value) && is_numeric($value)) {
@@ -99,11 +92,8 @@ protected function getSheet(): Worksheet
      * Excel handles text/logical/empty cells differently when
      * passed directly as arguments as opposed to cell references or arrays.
      * This function will test both approaches.
-     *
-     * @param mixed $expectedResult
-     * @param array $args
      */
-    protected function runTestCases(string $functionName, $expectedResult, ...$args): void
+    protected function runTestCases(string $functionName, mixed $expectedResult, mixed ...$args): void
     {
         if (is_array($expectedResult)) {
             $this->runTestCaseReference($functionName, $expectedResult[0], ...$args);
@@ -118,11 +108,8 @@ protected function runTestCases(string $functionName, $expectedResult, ...$args)
      * Excel handles text/logical/empty cells differently when
      * passed directly as arguments as opposed to cell references or arrays.
      * This functions tests passing as arrays.
-     *
-     * @param mixed $expectedResult
-     * @param array $args
      */
-    protected function runTestCaseReference(string $functionName, $expectedResult, ...$args): void
+    protected function runTestCaseReference(string $functionName, mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -142,7 +129,7 @@ protected function runTestCaseReference(string $functionName, $expectedResult, .
                 $arrayArg .= '}';
                 $formula .= "$comma$arrayArg";
                 $comma = ',';
-            } else { // @phpstan-ignore-line
+            } else {
                 $cellId = "A$row";
                 $formula .= "$comma$cellId";
                 $comma = ',';
@@ -158,11 +145,8 @@ protected function runTestCaseReference(string $functionName, $expectedResult, .
      * Excel handles text/logical/empty cells differently when
      * passed directly as arguments as opposed to cell references or arrays.
      * This functions tests passing as direct arguments.
-     *
-     * @param mixed $expectedResult
-     * @param array $args
      */
-    protected function runTestCaseDirect(string $functionName, $expectedResult, ...$args): void
+    protected function runTestCaseDirect(string $functionName, mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -175,7 +159,7 @@ protected function runTestCaseDirect(string $functionName, $expectedResult, ...$
                     $comma = ',';
                     $formula .= $this->convertToString($arrayItem);
                 }
-            } else { // @phpstan-ignore-line
+            } else {
                 $formula .= $comma;
                 $comma = ',';
                 $formula .= $this->convertToString($arg);
@@ -189,11 +173,8 @@ protected function runTestCaseDirect(string $functionName, $expectedResult, ...$
     /**
      * Excel seems to reject bracket notation for literal arrays
      * for some functions.
-     *
-     * @param mixed $expectedResult
-     * @param array $args
      */
-    protected function runTestCaseNoBracket(string $functionName, $expectedResult, ...$args): void
+    protected function runTestCaseNoBracket(string $functionName, mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -213,7 +194,7 @@ protected function runTestCaseNoBracket(string $functionName, $expectedResult, .
                 }
                 $formula .= "$comma$arrayRange";
                 $comma = ',';
-            } else { // @phpstan-ignore-line
+            } else {
                 $cellId = "A$row";
                 $formula .= "$comma$cellId";
                 $comma = ',';
@@ -229,10 +210,7 @@ protected function runTestCaseNoBracket(string $functionName, $expectedResult, .
         self::assertEqualsWithDelta($expectedResult, $sheet->getCell('Z99')->getCalculatedValue(), 1.0e-8, 'arguments supplied as ranges');
     }
 
-    /**
-     * @param mixed $arg
-     */
-    private function convertToString($arg): string
+    private function convertToString(mixed $arg): string
     {
         if (is_string($arg)) {
             return '"' . $arg . '"';
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AveDevTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AveDevTest.php
index 37a06626b6..ea9c61ef84 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AveDevTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AveDevTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class AveDevTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAVEDEV
-     *
-     * @param mixed $expectedResult
      */
-    public function testAVEDEV($expectedResult, ...$args): void
+    public function testAVEDEV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('AVEDEV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageATest.php
index 8a0f35442b..48788ab402 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class AverageATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAVERAGEA
-     *
-     * @param mixed $expectedResult
      */
-    public function testAVERAGEA($expectedResult, ...$args): void
+    public function testAVERAGEA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('AVERAGEA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIf2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIf2Test.php
index 1899239f82..4cbdee0636 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIf2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIf2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfTest.php
index bb91aead14..2b23a77d24 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -8,10 +10,8 @@ class AverageIfTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAVERAGEIF
-     *
-     * @param mixed $expectedResult
      */
-    public function testAVERAGEIF($expectedResult, ...$args): void
+    public function testAVERAGEIF(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('AVERAGEIF', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfsTest.php
index 10a466b625..e3f835809d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageIfsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -8,10 +10,8 @@ class AverageIfsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAVERAGEIFS
-     *
-     * @param mixed $expectedResult
      */
-    public function testAVERAGEIFS($expectedResult, ...$args): void
+    public function testAVERAGEIFS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('AVERAGEIFS', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageTest.php
index f8c8e41855..078a8313b2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/AverageTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class AverageTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerAVERAGE
-     *
-     * @param mixed $expectedResult
      */
-    public function testAVERAGE($expectedResult, ...$args): void
+    public function testAVERAGE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('AVERAGE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaDistTest.php
index b34dc5ee0b..2a25cbfe6f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class BetaDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBETADIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testBETADIST($expectedResult, ...$args): void
+    public function testBETADIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('BETADIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaInvTest.php
index b035abd6d2..eab0cf4ba1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BetaInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class BetaInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBETAINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testBETAINV($expectedResult, ...$args): void
+    public function testBETAINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('BETAINV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistRangeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistRangeTest.php
index 3970b02661..9a8ac452fc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class BinomDistRangeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBINOMDISTRANGE
-     *
-     * @param mixed $expectedResult
      */
-    public function testBINOMDISTRANGE($expectedResult, ...$args): void
+    public function testBINOMDISTRANGE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('BINOM.DIST.RANGE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistTest.php
index 9d89628eac..5f824d7178 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class BinomDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBINOMDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testBINOMDIST($expectedResult, ...$args): void
+    public function testBINOMDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('BINOMDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomInvTest.php
index cd15517df5..ecd12285c2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/BinomInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class BinomInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBINOMINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testBINOMINV($expectedResult, ...$args): void
+    public function testBINOMINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('BINOM.INV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistLeftTailTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistLeftTailTest.php
index 81db209da4..a9319cee65 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistLeftTailTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistLeftTailTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ChiDistLeftTailTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCHIDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testCHIDIST($expectedResult, ...$args): void
+    public function testCHIDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('CHISQ.DIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistRightTailTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistRightTailTest.php
index 06ba2d3de5..94835eb614 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistRightTailTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiDistRightTailTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ChiDistRightTailTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCHIDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testCHIDIST($expectedResult, ...$args): void
+    public function testCHIDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('CHISQ.DIST.RT', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvLeftTailTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvLeftTailTest.php
index 858cfa3ff5..d12f3b3f49 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvLeftTailTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvLeftTailTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ChiInvLeftTailTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCHIINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testCHIINV($expectedResult, ...$args): void
+    public function testCHIINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('CHISQ.INV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvRightTailTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvRightTailTest.php
index 79c8531239..82da0a6d64 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvRightTailTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiInvRightTailTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ChiInvRightTailTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCHIINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testCHIINV($expectedResult, ...$args): void
+    public function testCHIINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('CHISQ.INV.RT', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiTestTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiTestTest.php
index 7f9ea55a78..0059a9de8b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiTestTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ChiTestTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -10,12 +12,8 @@ class ChiTestTest extends TestCase
 {
     /**
      * @dataProvider providerCHITEST
-     *
-     * @param mixed $expectedResult
-     * @param mixed $actual
-     * @param mixed $expected
      */
-    public function testCHITEST($expectedResult, $actual, $expected): void
+    public function testCHITEST(mixed $expectedResult, mixed $actual, mixed $expected): void
     {
         $result = Statistical\Distributions\ChiSquared::test($actual, $expected);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ConfidenceTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ConfidenceTest.php
index 43d0ee8bae..006ad32eb0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ConfidenceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ConfidenceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ConfidenceTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCONFIDENCE
-     *
-     * @param mixed $expectedResult
      */
-    public function testCONFIDENCE($expectedResult, ...$args): void
+    public function testCONFIDENCE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('CONFIDENCE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CorrelTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CorrelTest.php
index 204cf34d73..e832a89e7b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CorrelTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CorrelTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -9,12 +11,8 @@ class CorrelTest extends TestCase
 {
     /**
      * @dataProvider providerCORREL
-     *
-     * @param mixed $expectedResult
-     * @param mixed $xargs
-     * @param mixed $yargs
      */
-    public function testCORREL($expectedResult, $xargs, $yargs): void
+    public function testCORREL(mixed $expectedResult, mixed $xargs, mixed $yargs): void
     {
         $result = Statistical\Trends::CORREL($xargs, $yargs);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountATest.php
index 2519789e16..381b1384d2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class CountATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUNTA
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUNTA($expectedResult, ...$args): void
+    public function testCOUNTA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('COUNTA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountBlankTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountBlankTest.php
index ec266a8967..e5f44f78d1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountBlankTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountBlankTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -8,10 +10,8 @@ class CountBlankTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUNTBLANK
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUNTBLANK($expectedResult, ...$args): void
+    public function testCOUNTBLANK(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('COUNTBLANK', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfTest.php
index dbfb5facae..794751d6f0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class CountIfTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUNTIF
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUNTIF($expectedResult, ...$args): void
+    public function testCOUNTIF(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('COUNTIF', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfsTest.php
index 382e8a6fda..54c8a05bef 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountIfsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 // TODO There are some commented out cases which don't return correct value
@@ -7,10 +9,8 @@ class CountIfsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOUNTIFS
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOUNTIFS($expectedResult, ...$args): void
+    public function testCOUNTIFS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('COUNTIFS', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountTest.php
index b8a775a2af..ef951be3f1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CountTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class CountTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerBasicCOUNT
-     *
-     * @param mixed $expectedResult
      */
-    public function testBasicCOUNT($expectedResult, ...$args): void
+    public function testBasicCOUNT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('COUNT', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerBasicCOUNT(): array
 
     /**
      * @dataProvider providerExcelCOUNT
-     *
-     * @param mixed $expectedResult
      */
-    public function testExcelCOUNT($expectedResult, ...$args): void
+    public function testExcelCOUNT(mixed $expectedResult, mixed ...$args): void
     {
         if (is_array($args[0])) {
             $this->runTestCaseNoBracket('COUNT', $expectedResult, ...$args);
@@ -40,10 +38,8 @@ public static function providerExcelCOUNT(): array
 
     /**
      * @dataProvider providerOpenOfficeCOUNT
-     *
-     * @param mixed $expectedResult
      */
-    public function testOpenOfficeCOUNT($expectedResult, ...$args): void
+    public function testOpenOfficeCOUNT(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         if (is_array($args[0])) {
@@ -60,10 +56,8 @@ public static function providerOpenOfficeCOUNT(): array
 
     /**
      * @dataProvider providerGnumericCOUNT
-     *
-     * @param mixed $expectedResult
      */
-    public function testGnumericCOUNT($expectedResult, ...$args): void
+    public function testGnumericCOUNT(mixed $expectedResult, mixed ...$args): void
     {
         $this->setGnumeric();
         $this->runTestCaseNoBracket('COUNT', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CovarTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CovarTest.php
index 4c04f86790..63b11e8d3f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CovarTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/CovarTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class CovarTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCOVAR
-     *
-     * @param mixed $expectedResult
      */
-    public function testCOVAR($expectedResult, ...$args): void
+    public function testCOVAR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('COVAR', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/DevSqTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/DevSqTest.php
index 8f2b282d03..e239e105a9 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/DevSqTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/DevSqTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class DevSqTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDEVSQ
-     *
-     * @param mixed $expectedResult
      */
-    public function testDEVSQ($expectedResult, ...$args): void
+    public function testDEVSQ(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('DEVSQ', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ExponDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ExponDistTest.php
index 018eee002c..2cb5b64cbb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ExponDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ExponDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ExponDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerEXPONDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testEXPONDIST($expectedResult, ...$args): void
+    public function testEXPONDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('EXPONDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FDistTest.php
index 2a1db8993b..6c6478f288 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class FDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testFDIST($expectedResult, ...$args): void
+    public function testFDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('F.DIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherInvTest.php
index 875724efa6..aa3189742e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class FisherInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFISHERINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testFISHERINV($expectedResult, ...$args): void
+    public function testFISHERINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('FISHERINV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherTest.php
index de20c2d443..352a3afc53 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/FisherTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class FisherTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFISHER
-     *
-     * @param mixed $expectedResult
      */
-    public function testFISHER($expectedResult, ...$args): void
+    public function testFISHER(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('FISHER', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ForecastTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ForecastTest.php
index c8d944cbff..396e69e0ba 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ForecastTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ForecastTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,8 @@ class ForecastTest extends TestCase
 {
     /**
      * @dataProvider providerFORECAST
-     *
-     * @param mixed $expectedResult
      */
-    public function testFORECAST($expectedResult, ...$args): void
+    public function testFORECAST(mixed $expectedResult, mixed ...$args): void
     {
         $result = Statistical\Trends::FORECAST(...$args);
         self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaDistTest.php
index 7c5f9fdab8..64ef50a5f3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class GammaDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGAMMADIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testGAMMADIST($expectedResult, ...$args): void
+    public function testGAMMADIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('GAMMA.DIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaInvTest.php
index dcddf82cd0..b3d1a3409b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class GammaInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGAMMAINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testGAMMAINV($expectedResult, ...$args): void
+    public function testGAMMAINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('GAMMA.INV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaLnTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaLnTest.php
index e30aaa37bf..8c9c4c76a3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaLnTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaLnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class GammaLnTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGAMMALN
-     *
-     * @param mixed $expectedResult
      */
-    public function testGAMMALN($expectedResult, ...$args): void
+    public function testGAMMALN(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('GAMMALN', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaTest.php
index 412133fdcf..9db243cc02 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GammaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class GammaTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGAMMA
-     *
-     * @param mixed $expectedResult
      */
-    public function testGAMMA($expectedResult, ...$args): void
+    public function testGAMMA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('GAMMA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GaussTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GaussTest.php
index 57d1afd438..4fb98f5ec5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GaussTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GaussTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class GaussTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGAUSS
-     *
-     * @param mixed $expectedResult
      */
-    public function testGAUSS($expectedResult, ...$args): void
+    public function testGAUSS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('GAUSS', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GeoMeanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GeoMeanTest.php
index ead0233f54..f5b8b91b4f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GeoMeanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GeoMeanTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class GeoMeanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerGEOMEAN
-     *
-     * @param mixed $expectedResult
      */
-    public function testGEOMEAN($expectedResult, ...$args): void
+    public function testGEOMEAN(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('GEOMEAN', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GrowthTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GrowthTest.php
index ea7a64e4f5..51d379a8d9 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GrowthTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/GrowthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -10,10 +12,8 @@ class GrowthTest extends TestCase
 {
     /**
      * @dataProvider providerGROWTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testGROWTH($expectedResult, array $yValues, array $xValues, ?array $newValues = null, ?bool $const = null): void
+    public function testGROWTH(mixed $expectedResult, array $yValues, array $xValues, ?array $newValues = null, ?bool $const = null): void
     {
         if ($newValues === null) {
             $result = Statistical\Trends::GROWTH($yValues, $xValues);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HarMeanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HarMeanTest.php
index 40f3f0c7e4..497f8127cc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HarMeanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HarMeanTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class HarMeanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerHARMEAN
-     *
-     * @param mixed $expectedResult
      */
-    public function testHARMEAN($expectedResult, ...$args): void
+    public function testHARMEAN(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('HARMEAN', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HypGeomDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HypGeomDistTest.php
index 34d8b19210..b240d874b0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HypGeomDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/HypGeomDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class HypGeomDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerHYPGEOMDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testHYPGEOMDIST($expectedResult, ...$args): void
+    public function testHYPGEOMDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('HYPGEOMDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/InterceptTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/InterceptTest.php
index d50a6836b8..c340c98997 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/InterceptTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/InterceptTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class InterceptTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerINTERCEPT
-     *
-     * @param mixed $expectedResult
      */
-    public function testINTERCEPT($expectedResult, ...$args): void
+    public function testINTERCEPT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('INTERCEPT', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/KurtTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/KurtTest.php
index 95776acf97..1b2d791683 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/KurtTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/KurtTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class KurtTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerKURT
-     *
-     * @param mixed $expectedResult
      */
-    public function testKURT($expectedResult, ...$args): void
+    public function testKURT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('KURT', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LargeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LargeTest.php
index 848b4b7615..de1e4aa1ea 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LargeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LargeTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class LargeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLARGE
-     *
-     * @param mixed $expectedResult
      */
-    public function testLARGE($expectedResult, ...$args): void
+    public function testLARGE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('LARGE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LinEstTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LinEstTest.php
index 485857aef7..1c86b7128d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LinEstTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LinEstTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -10,13 +12,8 @@ class LinEstTest extends TestCase
 {
     /**
      * @dataProvider providerLINEST
-     *
-     * @param mixed $xValues
-     * @param mixed $yValues
-     * @param mixed $const
-     * @param mixed $stats
      */
-    public function testLINEST(array $expectedResult, $yValues, $xValues, $const, $stats): void
+    public function testLINEST(array $expectedResult, mixed $yValues, mixed $xValues, mixed $const, mixed $stats): void
     {
         $result = Statistical\Trends::LINEST($yValues, $xValues, $const, $stats);
         self::assertIsArray($result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogEstTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogEstTest.php
index ca931d8fca..9c1314eb7b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogEstTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogEstTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -10,13 +12,8 @@ class LogEstTest extends TestCase
 {
     /**
      * @dataProvider providerLOGEST
-     *
-     * @param mixed $xValues
-     * @param mixed $yValues
-     * @param mixed $const
-     * @param mixed $stats
      */
-    public function testLOGEST(array $expectedResult, $yValues, $xValues, $const, $stats): void
+    public function testLOGEST(array $expectedResult, mixed $yValues, mixed $xValues, mixed $const, mixed $stats): void
     {
         $result = Statistical\Trends::LOGEST($yValues, $xValues, $const, $stats);
         self::assertIsArray($result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogInvTest.php
index 996195c8fd..fce4a4b246 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class LogInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLOGINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testLOGINV($expectedResult, ...$args): void
+    public function testLOGINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('LOGINV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDist2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDist2Test.php
index 6238540f39..0857e54249 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDist2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDist2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class LogNormDist2Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLOGNORMDIST2
-     *
-     * @param mixed $expectedResult
      */
-    public function testLOGNORMDIST2($expectedResult, ...$args): void
+    public function testLOGNORMDIST2(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('LOGNORM.DIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDistTest.php
index 89f04b0890..fcb01d5a44 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/LogNormDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class LogNormDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLOGNORMDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testLOGNORMDIST($expectedResult, ...$args): void
+    public function testLOGNORMDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('LOGNORMDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxATest.php
index ea7af4a1fe..4e65e2db45 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MaxATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMAXA
-     *
-     * @param mixed $expectedResult
      */
-    public function testMAXA($expectedResult, ...$args): void
+    public function testMAXA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('MAXA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxIfsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxIfsTest.php
index 86944471e3..25a7ac696a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxIfsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxIfsTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MaxIfsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMAXIFS
-     *
-     * @param mixed $expectedResult
      */
-    public function testMAXIFS($expectedResult, ...$args): void
+    public function testMAXIFS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('MAXIFS', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxTest.php
index bf7db628ea..ea1e5110bd 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MaxTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MaxTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMAX
-     *
-     * @param mixed $expectedResult
      */
-    public function testMAX($expectedResult, ...$args): void
+    public function testMAX(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('MAX', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MedianTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MedianTest.php
index aa568fdcc1..2eeaf6042d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MedianTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MedianTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MedianTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMEDIAN
-     *
-     * @param mixed $expectedResult
      */
-    public function testMEDIAN($expectedResult, ...$args): void
+    public function testMEDIAN(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('MEDIAN', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinATest.php
index 7daa156195..28d417dae7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MinATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMINA
-     *
-     * @param mixed $expectedResult
      */
-    public function testMINA($expectedResult, ...$args): void
+    public function testMINA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('MINA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinIfsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinIfsTest.php
index d3dda839e0..7fb91bfbcb 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinIfsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinIfsTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MinIfsTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMINIFS
-     *
-     * @param mixed $expectedResult
      */
-    public function testMINIFS($expectedResult, ...$args): void
+    public function testMINIFS(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('MINIFS', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinTest.php
index 03493c21ed..c699cfedf3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MinTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class MinTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerMIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testMIN($expectedResult, ...$args): void
+    public function testMIN(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('MIN', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ModeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ModeTest.php
index aed9188e4a..5ae2c4977c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ModeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ModeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -9,10 +11,8 @@ class ModeTest extends TestCase
 {
     /**
      * @dataProvider providerMODE
-     *
-     * @param mixed $expectedResult
      */
-    public function testMODE($expectedResult, string $str): void
+    public function testMODE(mixed $expectedResult, string $str): void
     {
         $workbook = new Spreadsheet();
         $sheet = $workbook->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MovedFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MovedFunctionsTest.php
index e51e8823fa..6b0b8c6283 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MovedFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/MovedFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NegBinomDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NegBinomDistTest.php
index 6bd286fb66..7725556eef 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NegBinomDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NegBinomDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NegBinomDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNEGBINOMDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testNEGBINOMDIST($expectedResult, ...$args): void
+    public function testNEGBINOMDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('NEGBINOMDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormDistTest.php
index 590a2b4258..ba62123ec3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NormDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNORMDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testNORMDIST($expectedResult, ...$args): void
+    public function testNORMDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('NORMDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormInvTest.php
index a287d6684a..5aa42fc85b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NormInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNORMINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testNORMINV($expectedResult, ...$args): void
+    public function testNORMINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('NORMINV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDist2Test.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDist2Test.php
index b3c9df24f4..c85c125c7c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDist2Test.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDist2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NormSDist2Test extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNORMSDIST2
-     *
-     * @param mixed $expectedResult
      */
-    public function testNORMSDIST2($expectedResult, ...$args): void
+    public function testNORMSDIST2(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('NORM.S.DIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDistTest.php
index 4306e862e7..95d8ff32de 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NormSDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNORMSDIST
-     *
-     * @param mixed $expectedResult
      */
-    public function testNORMSDIST($expectedResult, ...$args): void
+    public function testNORMSDIST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('NORMSDIST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSInvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSInvTest.php
index 131a7b8e5b..e935538023 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSInvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/NormSInvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class NormSInvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerNORMSINV
-     *
-     * @param mixed $expectedResult
      */
-    public function testNORMSINV($expectedResult, ...$args): void
+    public function testNORMSINV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('NORMSINV', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentRankTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentRankTest.php
index 200f88e9b9..153b768224 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentRankTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentRankTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class PercentRankTest extends AllSetupTeardown
@@ -7,12 +9,9 @@ class PercentRankTest extends AllSetupTeardown
     /**
      * @dataProvider providerPERCENTRANK
      *
-     * @param mixed $expectedResult
      * @param mixed[] $valueSet
-     * @param mixed $value
-     * @param mixed $digits
      */
-    public function testPERCENTRANK($expectedResult, $valueSet, $value, $digits = null): void
+    public function testPERCENTRANK(mixed $expectedResult, mixed $valueSet, mixed $value, mixed $digits = null): void
     {
         if ($digits === null) {
             $this->runTestCaseReference('PERCENTRANK', $expectedResult, $valueSet, $value);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentileTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentileTest.php
index 35dd358497..47faff9e31 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentileTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PercentileTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class PercentileTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPERCENTILE
-     *
-     * @param mixed $expectedResult
      */
-    public function testPERCENTILE($expectedResult, ...$args): void
+    public function testPERCENTILE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('PERCENTILE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutTest.php
index d680a5a2b7..75a7999564 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class PermutTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPERMUT
-     *
-     * @param mixed $expectedResult
      */
-    public function testPERMUT($expectedResult, ...$args): void
+    public function testPERMUT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('PERMUT', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutationATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutationATest.php
index 29533d1e5e..2cfc6a567d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutationATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PermutationATest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class PermutationATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPERMUT
-     *
-     * @param mixed $expectedResult
      */
-    public function testPERMUT($expectedResult, ...$args): void
+    public function testPERMUT(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('PERMUTATIONA', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PoissonTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PoissonTest.php
index 74ae8a6147..2233a74eca 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PoissonTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/PoissonTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class PoissonTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPOISSON
-     *
-     * @param mixed $expectedResult
      */
-    public function testPOISSON($expectedResult, ...$args): void
+    public function testPOISSON(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('POISSON', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/QuartileTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/QuartileTest.php
index 343ac8eb40..daf658b849 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/QuartileTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/QuartileTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class QuartileTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerQUARTILE
-     *
-     * @param mixed $expectedResult
      */
-    public function testQUARTILE($expectedResult, ...$args): void
+    public function testQUARTILE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('QUARTILE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RankTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RankTest.php
index c3f8bb2b4b..5777a8f2d0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RankTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RankTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class RankTest extends AllSetupTeardown
@@ -7,12 +9,9 @@ class RankTest extends AllSetupTeardown
     /**
      * @dataProvider providerRANK
      *
-     * @param mixed $expectedResult
-     * @param mixed $value
      * @param mixed[] $valueSet
-     * @param mixed $order
      */
-    public function testRANK($expectedResult, $value, $valueSet, $order = null): void
+    public function testRANK(mixed $expectedResult, mixed $value, $valueSet, mixed $order = null): void
     {
         if ($order === null) {
             $this->runTestCaseReference('RANK', $expectedResult, $value, $valueSet);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RsqTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RsqTest.php
index 51ce4ee18f..fba99b1b82 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RsqTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/RsqTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class RsqTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerRSQ
-     *
-     * @param mixed $expectedResult
      */
-    public function testRSQ($expectedResult, ...$args): void
+    public function testRSQ(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('RSQ', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SkewTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SkewTest.php
index 264d29de19..f88287cc33 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SkewTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SkewTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class SkewTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSKEW
-     *
-     * @param mixed $expectedResult
      */
-    public function testSKEW($expectedResult, array $args): void
+    public function testSKEW(mixed $expectedResult, array $args): void
     {
         $this->runTestCaseReference('SKEW', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SlopeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SlopeTest.php
index 0d7fe282b6..12220561b7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SlopeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SlopeTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class SlopeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSLOPE
-     *
-     * @param mixed $expectedResult
      */
-    public function testSLOPE($expectedResult, ...$args): void
+    public function testSLOPE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseNoBracket('SLOPE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SmallTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SmallTest.php
index 86dbc481d4..13dc6f99c4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SmallTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SmallTest.php
@@ -1,17 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class SmallTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSMALL
-     *
-     * @param mixed $expectedResult
-     * @param mixed $values
-     * @param mixed $position
      */
-    public function testSMALL($expectedResult, $values, $position): void
+    public function testSMALL(mixed $expectedResult, mixed $values, mixed $position): void
     {
         $this->runTestCaseReference('SMALL', $expectedResult, $values, $position);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevATest.php
index 1268d44034..c6964f9487 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class StDevATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSTDEVA
-     *
-     * @param mixed $expectedResult
      */
-    public function testSTDEVA($expectedResult, ...$args): void
+    public function testSTDEVA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('STDEVA', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerSTDEVA(): array
 
     /**
      * @dataProvider providerOdsSTDEVA
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsSTDEVA($expectedResult, ...$args): void
+    public function testOdsSTDEVA(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCaseReference('STDEVA', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPATest.php
index 9d5389ed16..db309b2f7a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class StDevPATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSTDEVPA
-     *
-     * @param mixed $expectedResult
      */
-    public function testSTDEVPA($expectedResult, ...$args): void
+    public function testSTDEVPA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('STDEVPA', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerSTDEVPA(): array
 
     /**
      * @dataProvider providerOdsSTDEVPA
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsSTDEVPA($expectedResult, ...$args): void
+    public function testOdsSTDEVPA(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCaseReference('STDEVPA', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPTest.php
index 60057d218b..89898d2a1e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevPTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class StDevPTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSTDEVP
-     *
-     * @param mixed $expectedResult
      */
-    public function testSTDEVP($expectedResult, ...$args): void
+    public function testSTDEVP(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('STDEVP', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerSTDEVP(): array
 
     /**
      * @dataProvider providerOdsSTDEVP
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsSTDEVP($expectedResult, ...$args): void
+    public function testOdsSTDEVP(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCaseReference('STDEVP', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevTest.php
index eb607d8289..b920621533 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StDevTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class StDevTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSTDEV
-     *
-     * @param mixed $expectedResult
      */
-    public function testSTDEV($expectedResult, ...$args): void
+    public function testSTDEV(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('STDEV', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerSTDEV(): array
 
     /**
      * @dataProvider providerOdsSTDEV
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsSTDEV($expectedResult, ...$args): void
+    public function testOdsSTDEV(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCaseReference('STDEV', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StandardizeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StandardizeTest.php
index 3a36ddfbb3..8defe4c03c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StandardizeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/StandardizeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class StandardizeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSTANDARDIZE
-     *
-     * @param mixed $expectedResult
      */
-    public function testSTANDARDIZE($expectedResult, ...$args): void
+    public function testSTANDARDIZE(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('STANDARDIZE', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SteyxTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SteyxTest.php
index 5971aaf8e7..5c195630a1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SteyxTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/SteyxTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class SteyxTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSTEYX
-     *
-     * @param mixed $expectedResult
      */
-    public function testSTEYX($expectedResult, array $xargs, array $yargs): void
+    public function testSTEYX(mixed $expectedResult, array $xargs, array $yargs): void
     {
         //$result = Statistical\Trends::STEYX($xargs, $yargs);
         //self::assertEqualsWithDelta($expectedResult, $result, 1E-12);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TDistTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TDistTest.php
index 704b4d4ae7..c57deb2663 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TDistTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TDistTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,13 +10,8 @@ class TDistTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTDIST
-     *
-     * @param mixed $expectedResult
-     * @param mixed $degrees
-     * @param mixed $value
-     * @param mixed $tails
      */
-    public function testTDIST($expectedResult, $value, $degrees, $tails): void
+    public function testTDIST(mixed $expectedResult, mixed $value, mixed $degrees, mixed $tails): void
     {
         $this->runTestCaseReference('TDIST', $expectedResult, $value, $degrees, $tails);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TinvTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TinvTest.php
index ebe4abc6a0..ed16e9dbaa 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TinvTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TinvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class TinvTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTINV
-     *
-     * @param mixed $expectedResult
-     * @param mixed $probability
-     * @param mixed $degrees
      */
-    public function testTINV($expectedResult, $probability, $degrees): void
+    public function testTINV(mixed $expectedResult, mixed $probability, mixed $degrees): void
     {
         $this->runTestCaseReference('TINV', $expectedResult, $probability, $degrees);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrendTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrendTest.php
index 5aa32bda33..1a09ce9b4c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrendTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrendTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Statistical;
@@ -10,10 +12,8 @@ class TrendTest extends TestCase
 {
     /**
      * @dataProvider providerGROWTH
-     *
-     * @param mixed $expectedResult
      */
-    public function testTREND($expectedResult, array $yValues, array $xValues, ?array $newValues = null, ?bool $const = null): void
+    public function testTREND(mixed $expectedResult, array $yValues, array $xValues, ?array $newValues = null, ?bool $const = null): void
     {
         if ($newValues === null) {
             $result = Statistical\Trends::TREND($yValues, $xValues);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrimMeanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrimMeanTest.php
index c867ff82a3..1e6adfdcb5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrimMeanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/TrimMeanTest.php
@@ -1,16 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class TrimMeanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTRIMMEAN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $percentage
      */
-    public function testTRIMMEAN($expectedResult, array $args, $percentage): void
+    public function testTRIMMEAN(mixed $expectedResult, array $args, mixed $percentage): void
     {
         $this->runTestCaseReference('TRIMMEAN', $expectedResult, $args, $percentage);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarATest.php
index 4872310832..084a452e42 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class VarATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerVARA
-     *
-     * @param mixed $expectedResult
      */
-    public function testVARA($expectedResult, ...$args): void
+    public function testVARA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('VARA', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerVARA(): array
 
     /**
      * @dataProvider providerOdsVARA
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsVARA($expectedResult, ...$args): void
+    public function testOdsVARA(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCases('VARA', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPATest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPATest.php
index 7c128b6f96..9c1e62fdb7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPATest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPATest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class VarPATest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerVARPA
-     *
-     * @param mixed $expectedResult
      */
-    public function testVARPA($expectedResult, ...$args): void
+    public function testVARPA(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('VARPA', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerVARPA(): array
 
     /**
      * @dataProvider providerOdsVARPA
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsVARPA($expectedResult, ...$args): void
+    public function testOdsVARPA(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCases('VARPA', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPTest.php
index 5ab6e60951..45f46d08b6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarPTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class VarPTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerVARP
-     *
-     * @param mixed $expectedResult
      */
-    public function testVARP($expectedResult, ...$args): void
+    public function testVARP(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('VARP', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerVARP(): array
 
     /**
      * @dataProvider providerOdsVARP
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsVARP($expectedResult, ...$args): void
+    public function testOdsVARP(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCases('VARP', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarTest.php
index 088fd4bae7..c565b4177c 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/VarTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 class VarTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerVAR
-     *
-     * @param mixed $expectedResult
      */
-    public function testVAR($expectedResult, ...$args): void
+    public function testVAR(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('VAR', $expectedResult, ...$args);
     }
@@ -21,10 +21,8 @@ public static function providerVAR(): array
 
     /**
      * @dataProvider providerOdsVAR
-     *
-     * @param mixed $expectedResult
      */
-    public function testOdsVAR($expectedResult, ...$args): void
+    public function testOdsVAR(mixed $expectedResult, mixed ...$args): void
     {
         $this->setOpenOffice();
         $this->runTestCases('VAR', $expectedResult, ...$args);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/WeibullTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/WeibullTest.php
index 3c6f8116be..533477525f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/WeibullTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/WeibullTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class WeibullTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerWEIBULL
-     *
-     * @param mixed $expectedResult
      */
-    public function testWEIBULL($expectedResult, ...$args): void
+    public function testWEIBULL(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCases('WEIBULL', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ZTestTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ZTestTest.php
index 492fdd860d..32ae58a1c6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ZTestTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Statistical/ZTestTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Statistical;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class ZTestTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerZTEST
-     *
-     * @param mixed $expectedResult
      */
-    public function testZTEST($expectedResult, ...$args): void
+    public function testZTEST(mixed $expectedResult, mixed ...$args): void
     {
         $this->runTestCaseReference('ZTEST', $expectedResult, ...$args);
     }
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/AllSetupTeardown.php
index e0343b2b87..63f2e01c82 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/AllSetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalcException;
@@ -12,15 +14,9 @@
 
 class AllSetupTeardown extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
-    /**
-     * @var string
-     */
-    private $locale;
+    private string $locale;
 
     /**
      * @var ?Spreadsheet
@@ -59,20 +55,14 @@ protected static function setGnumeric(): void
         Functions::setCompatibilityMode(Functions::COMPATIBILITY_GNUMERIC);
     }
 
-    /**
-     * @param mixed $expectedResult
-     */
-    protected function mightHaveException($expectedResult): void
+    protected function mightHaveException(mixed $expectedResult): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(CalcException::class);
         }
     }
 
-    /**
-     * @param mixed $value
-     */
-    protected function setCell(string $cell, $value): void
+    protected function setCell(string $cell, mixed $value): void
     {
         if ($value !== null) {
             if (is_string($value) && is_numeric($value)) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ArrayToTextTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ArrayToTextTest.php
index a63bd6f24b..56d035729a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ArrayToTextTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ArrayToTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 class ArrayToTextTest extends AllSetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharNonPrintableTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharNonPrintableTest.php
index 035cdfa0e9..370ec308c9 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharNonPrintableTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharNonPrintableTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharTest.php
index df51f65303..e9549e4528 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CharTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CharTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCHAR
-     *
-     * @param mixed $expectedResult
-     * @param mixed $character
      */
-    public function testCHAR($expectedResult, $character = 'omitted'): void
+    public function testCHAR(mixed $expectedResult, mixed $character = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CleanTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CleanTest.php
index 3162a6baa6..7b83438cd2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CleanTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CleanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CleanTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCLEAN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testCLEAN($expectedResult, $value = 'omitted'): void
+    public function testCLEAN(mixed $expectedResult, mixed $value = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CodeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CodeTest.php
index 001ad6075e..e29c057a69 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CodeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/CodeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class CodeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCODE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $character
      */
-    public function testCODE($expectedResult, $character = 'omitted'): void
+    public function testCODE(mixed $expectedResult, mixed $character = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ConcatenateTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ConcatenateTest.php
index b5eeda7b6d..cfe5662634 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ConcatenateTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ConcatenateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -8,11 +10,8 @@ class ConcatenateTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerCONCATENATE
-     *
-     * @param mixed $expectedResult
-     * @param array $args
      */
-    public function testCONCATENATE($expectedResult, ...$args): void
+    public function testCONCATENATE(mixed $expectedResult, mixed ...$args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DeprecatedTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DeprecatedTest.php
index 5ecd3f507e..d6e50de05f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DeprecatedTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DeprecatedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\TextData;
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DollarTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DollarTest.php
index a4a1c6972b..19c9dc3b6d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DollarTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/DollarTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class DollarTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerDOLLAR
-     *
-     * @param mixed $expectedResult
-     * @param mixed $amount
-     * @param mixed $decimals
      */
-    public function testDOLLAR($expectedResult, $amount = 'omitted', $decimals = 'omitted'): void
+    public function testDOLLAR(mixed $expectedResult, mixed $amount = 'omitted', mixed $decimals = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ExactTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ExactTest.php
index 20293f1ed1..802b73e4cc 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ExactTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ExactTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class ExactTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerEXACT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $string1
-     * @param mixed $string2
      */
-    public function testEXACT($expectedResult, $string1 = 'omitted', $string2 = 'omitted'): void
+    public function testEXACT(mixed $expectedResult, mixed $string1 = 'omitted', mixed $string2 = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FindTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FindTest.php
index d649308373..6f5e187b83 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FindTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FindTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,13 +10,8 @@ class FindTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFIND
-     *
-     * @param mixed $expectedResult
-     * @param mixed $string1
-     * @param mixed $string2
-     * @param mixed $start
      */
-    public function testFIND($expectedResult, $string1 = 'omitted', $string2 = 'omitted', $start = 'omitted'): void
+    public function testFIND(mixed $expectedResult, mixed $string1 = 'omitted', mixed $string2 = 'omitted', mixed $start = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FixedTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FixedTest.php
index a820299dad..0ee5c1cc39 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FixedTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/FixedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,13 +10,8 @@ class FixedTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerFIXED
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
-     * @param mixed $decimals
-     * @param mixed $noCommas
      */
-    public function testFIXED($expectedResult, $number = 'omitted', $decimals = 'omitted', $noCommas = 'omitted'): void
+    public function testFIXED(mixed $expectedResult, mixed $number = 'omitted', mixed $decimals = 'omitted', mixed $noCommas = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LeftTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LeftTest.php
index 496eb0af92..4be89c238b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LeftTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LeftTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,11 +13,10 @@ class LeftTest extends AllSetupTeardown
     /**
      * @dataProvider providerLEFT
      *
-     * @param mixed $expectedResult
      * @param mixed $str string from which to extract
      * @param mixed $cnt number of characters to extract
      */
-    public function testLEFT($expectedResult, $str = 'omitted', $cnt = 'omitted'): void
+    public function testLEFT(mixed $expectedResult, mixed $str = 'omitted', mixed $cnt = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -40,13 +41,8 @@ public static function providerLEFT(): array
 
     /**
      * @dataProvider providerLocaleLEFT
-     *
-     * @param string $expectedResult
-     * @param mixed $value
-     * @param mixed $locale
-     * @param mixed $characters
      */
-    public function testLowerWithLocaleBoolean($expectedResult, $locale, $value, $characters): void
+    public function testLowerWithLocaleBoolean(string $expectedResult, mixed $locale, mixed $value, mixed $characters): void
     {
         $newLocale = Settings::setLocale($locale);
         if ($newLocale === false) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LenTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LenTest.php
index c22f40b6c6..e2db773ae4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LenTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LenTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class LenTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLEN
-     *
-     * @param mixed $expectedResult
-     * @param mixed $str
      */
-    public function testLEN($expectedResult, $str = 'omitted'): void
+    public function testLEN(mixed $expectedResult, mixed $str = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LowerTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LowerTest.php
index 1ea6ac9f71..7549a3a4a7 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LowerTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/LowerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -9,11 +11,8 @@ class LowerTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerLOWER
-     *
-     * @param mixed $expectedResult
-     * @param mixed $str
      */
-    public function testLOWER($expectedResult, $str = 'omitted'): void
+    public function testLOWER(mixed $expectedResult, mixed $str = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -34,12 +33,8 @@ public static function providerLOWER(): array
 
     /**
      * @dataProvider providerLocaleLOWER
-     *
-     * @param string $expectedResult
-     * @param mixed $value
-     * @param mixed $locale
      */
-    public function testLowerWithLocaleBoolean($expectedResult, $locale, $value): void
+    public function testLowerWithLocaleBoolean(string $expectedResult, mixed $locale, mixed $value): void
     {
         $newLocale = Settings::setLocale($locale);
         if ($newLocale === false) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/MidTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/MidTest.php
index 78f8273a4d..4a103f2bf5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/MidTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/MidTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,12 +13,11 @@ class MidTest extends AllSetupTeardown
     /**
      * @dataProvider providerMID
      *
-     * @param mixed $expectedResult
      * @param mixed $str string from which to extract
      * @param mixed $start position at which to start
      * @param mixed $cnt number of characters to extract
      */
-    public function testMID($expectedResult, $str = 'omitted', $start = 'omitted', $cnt = 'omitted'): void
+    public function testMID(mixed $expectedResult, mixed $str = 'omitted', mixed $start = 'omitted', mixed $cnt = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -46,14 +47,8 @@ public static function providerMID(): array
 
     /**
      * @dataProvider providerLocaleMID
-     *
-     * @param string $expectedResult
-     * @param mixed $value
-     * @param mixed $locale
-     * @param mixed $offset
-     * @param mixed $characters
      */
-    public function testMiddleWithLocaleBoolean($expectedResult, $locale, $value, $offset, $characters): void
+    public function testMiddleWithLocaleBoolean(string $expectedResult, mixed $locale, mixed $value, mixed $offset, mixed $characters): void
     {
         $newLocale = Settings::setLocale($locale);
         if ($newLocale === false) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/NumberValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/NumberValueTest.php
index 3b410cbd74..9dfa1fa205 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/NumberValueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/NumberValueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -10,13 +12,8 @@ class NumberValueTest extends AllSetupTeardown
 
     /**
      * @dataProvider providerNUMBERVALUE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $number
-     * @param mixed $decimal
-     * @param mixed $group
      */
-    public function testNUMBERVALUE($expectedResult, $number = 'omitted', $decimal = 'omitted', $group = 'omitted'): void
+    public function testNUMBERVALUE(mixed $expectedResult, mixed $number = 'omitted', mixed $decimal = 'omitted', mixed $group = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/OpenOfficeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/OpenOfficeTest.php
index 64e02e50b8..c7af96f64f 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/OpenOfficeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/OpenOfficeTest.php
@@ -1,15 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 class OpenOfficeTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerOpenOffice
-     *
-     * @param mixed $expectedResult
      */
-    public function testOpenOffice($expectedResult, string $formula): void
+    public function testOpenOffice(mixed $expectedResult, string $formula): void
     {
         $this->setOpenOffice();
         $this->mightHaveException($expectedResult);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ProperTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ProperTest.php
index 9f6e6f7b74..a3aee91439 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ProperTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ProperTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -9,11 +11,8 @@ class ProperTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerPROPER
-     *
-     * @param mixed $expectedResult
-     * @param mixed $str
      */
-    public function testPROPER($expectedResult, $str = 'omitted'): void
+    public function testPROPER(mixed $expectedResult, mixed $str = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -34,12 +33,8 @@ public static function providerPROPER(): array
 
     /**
      * @dataProvider providerLocaleLOWER
-     *
-     * @param string $expectedResult
-     * @param mixed $value
-     * @param mixed $locale
      */
-    public function testLowerWithLocaleBoolean($expectedResult, $locale, $value): void
+    public function testLowerWithLocaleBoolean(string $expectedResult, mixed $locale, mixed $value): void
     {
         $newLocale = Settings::setLocale($locale);
         if ($newLocale === false) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReplaceTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReplaceTest.php
index 64e38d796e..68a6f501e8 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReplaceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReplaceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,14 +10,8 @@ class ReplaceTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerREPLACE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $oldText
-     * @param mixed $start
-     * @param mixed $count
-     * @param mixed $newText
      */
-    public function testREPLACE($expectedResult, $oldText = 'omitted', $start = 'omitted', $count = 'omitted', $newText = 'omitted'): void
+    public function testREPLACE(mixed $expectedResult, mixed $oldText = 'omitted', mixed $start = 'omitted', mixed $count = 'omitted', mixed $newText = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReptTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReptTest.php
index 09355c71e9..8cbed14d3d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReptTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ReptTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class ReptTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerREPT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $val
-     * @param mixed $rpt
      */
-    public function testReptThroughEngine($expectedResult, $val = 'omitted', $rpt = 'omitted'): void
+    public function testReptThroughEngine(mixed $expectedResult, mixed $val = 'omitted', mixed $rpt = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/RightTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/RightTest.php
index 4c9210d669..d2bc683627 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/RightTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/RightTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -11,11 +13,10 @@ class RightTest extends AllSetupTeardown
     /**
      * @dataProvider providerRIGHT
      *
-     * @param mixed $expectedResult
      * @param mixed $str string from which to extract
      * @param mixed $cnt number of characters to extract
      */
-    public function testRIGHT($expectedResult, $str = 'omitted', $cnt = 'omitted'): void
+    public function testRIGHT(mixed $expectedResult, mixed $str = 'omitted', mixed $cnt = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -40,13 +41,8 @@ public static function providerRIGHT(): array
 
     /**
      * @dataProvider providerLocaleRIGHT
-     *
-     * @param string $expectedResult
-     * @param mixed $value
-     * @param mixed $locale
-     * @param mixed $characters
      */
-    public function testLowerWithLocaleBoolean($expectedResult, $locale, $value, $characters): void
+    public function testLowerWithLocaleBoolean(string $expectedResult, mixed $locale, mixed $value, mixed $characters): void
     {
         $newLocale = Settings::setLocale($locale);
         if ($newLocale === false) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SearchTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SearchTest.php
index aa08787cb5..5c441b7dd4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SearchTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SearchTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,13 +10,8 @@ class SearchTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSEARCH
-     *
-     * @param mixed $expectedResult
-     * @param mixed $findText
-     * @param mixed $withinText
-     * @param mixed $start
      */
-    public function testSEARCH($expectedResult, $findText = 'omitted', $withinText = 'omitted', $start = 'omitted'): void
+    public function testSEARCH(mixed $expectedResult, mixed $findText = 'omitted', mixed $withinText = 'omitted', mixed $start = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SubstituteTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SubstituteTest.php
index ced6cb00e5..9273302527 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SubstituteTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/SubstituteTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,14 +10,8 @@ class SubstituteTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerSUBSTITUTE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $text
-     * @param mixed $oldText
-     * @param mixed $newText
-     * @param mixed $instance
      */
-    public function testSUBSTITUTE($expectedResult, $text = 'omitted', $oldText = 'omitted', $newText = 'omitted', $instance = 'omitted'): void
+    public function testSUBSTITUTE(mixed $expectedResult, mixed $text = 'omitted', mixed $oldText = 'omitted', mixed $newText = 'omitted', mixed $instance = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TTest.php
index 991b6d9bcc..6f2bf123a2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class TTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testT($expectedResult, $value = 'no arguments'): void
+    public function testT(mixed $expectedResult, mixed $value = 'no arguments'): void
     {
         $this->mightHaveException($expectedResult);
         if ($value === 'no arguments') {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextAfterTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextAfterTest.php
index b64db024b3..9f50af3ef2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextAfterTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextAfterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 class TextAfterTest extends AllSetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextBeforeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextBeforeTest.php
index 6ee11bac46..05f0715ee0 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextBeforeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextBeforeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 class TextBeforeTest extends AllSetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextJoinTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextJoinTest.php
index 2000202131..e9a231a057 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextJoinTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextJoinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,10 +10,8 @@ class TextJoinTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTEXTJOIN
-     *
-     * @param mixed $expectedResult
      */
-    public function testTEXTJOIN($expectedResult, array $args): void
+    public function testTEXTJOIN(mixed $expectedResult, array $args): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextSplitTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextSplitTest.php
index c32f2f062a..9801d77d4b 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextSplitTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextSplitTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -12,10 +14,7 @@ private function setDelimiterArgument(array $argument, string $column): string
         return '{' . $column . implode(',' . $column, range(1, count($argument))) . '}';
     }
 
-    /**
-     * @param array|string $argument
-     */
-    private function setDelimiterValues(Worksheet $worksheet, string $column, $argument): void
+    private function setDelimiterValues(Worksheet $worksheet, string $column, array|string $argument): void
     {
         if (is_array($argument)) {
             foreach ($argument as $index => $value) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextTest.php
index f0a7e120fc..eedd8b93b4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,12 +10,8 @@ class TextTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTEXT
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
-     * @param mixed $format
      */
-    public function testTEXT($expectedResult, $value = 'omitted', $format = 'omitted'): void
+    public function testTEXT(mixed $expectedResult, mixed $value = 'omitted', mixed $format = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TrimTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TrimTest.php
index 45ae5374a0..30929afd9d 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TrimTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/TrimTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -8,11 +10,8 @@ class TrimTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerTRIM
-     *
-     * @param mixed $expectedResult
-     * @param mixed $character
      */
-    public function testTRIM($expectedResult, $character = 'omitted'): void
+    public function testTRIM(mixed $expectedResult, mixed $character = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/UpperTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/UpperTest.php
index dd5c82a790..964a2accb3 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/UpperTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/UpperTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -9,11 +11,8 @@ class UpperTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerUPPER
-     *
-     * @param mixed $expectedResult
-     * @param mixed $str
      */
-    public function testUPPER($expectedResult, $str = 'omitted'): void
+    public function testUPPER(mixed $expectedResult, mixed $str = 'omitted'): void
     {
         $this->mightHaveException($expectedResult);
         $sheet = $this->getSheet();
@@ -34,12 +33,8 @@ public static function providerUPPER(): array
 
     /**
      * @dataProvider providerLocaleLOWER
-     *
-     * @param string $expectedResult
-     * @param mixed $value
-     * @param mixed $locale
      */
-    public function testLowerWithLocaleBoolean($expectedResult, $locale, $value): void
+    public function testLowerWithLocaleBoolean(string $expectedResult, mixed $locale, mixed $value): void
     {
         $newLocale = Settings::setLocale($locale);
         if ($newLocale === false) {
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueTest.php
index 900af7dd79..c04dfe8798 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -7,20 +9,11 @@
 
 class ValueTest extends AllSetupTeardown
 {
-    /**
-     * @var string
-     */
-    private $currencyCode;
+    private string $currencyCode;
 
-    /**
-     * @var string
-     */
-    private $decimalSeparator;
+    private string $decimalSeparator;
 
-    /**
-     * @var string
-     */
-    private $thousandsSeparator;
+    private string $thousandsSeparator;
 
     protected function setUp(): void
     {
@@ -40,11 +33,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerVALUE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testVALUE($expectedResult, $value = 'omitted'): void
+    public function testVALUE(mixed $expectedResult, mixed $value = 'omitted'): void
     {
         StringHelper::setDecimalSeparator('.');
         StringHelper::setThousandsSeparator(' ');
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueToTextTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueToTextTest.php
index 6642bc6502..9aa277e440 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueToTextTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/TextData/ValueToTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\TextData;
 
 use PhpOffice\PhpSpreadsheet\Calculation\TextData\Format;
@@ -9,12 +11,8 @@ class ValueToTextTest extends AllSetupTeardown
 {
     /**
      * @dataProvider providerVALUE
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
-     * @param mixed $format
      */
-    public function testVALUETOTEXT($expectedResult, $value, $format): void
+    public function testVALUETOTEXT(mixed $expectedResult, mixed $value, mixed $format): void
     {
         $sheet = $this->getSheet();
         $this->setCell('A1', $value);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Web/UrlEncodeTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Web/UrlEncodeTest.php
index 82f60ef986..8ab1337f18 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Web/UrlEncodeTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Web/UrlEncodeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Web;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Web\Service;
@@ -9,11 +11,8 @@ class UrlEncodeTest extends TestCase
 {
     /**
      * @dataProvider providerURLENCODE
-     *
-     * @param string $expectedResult
-     * @param mixed $text
      */
-    public function testURLENCODE($expectedResult, $text): void
+    public function testURLENCODE(string $expectedResult, mixed $text): void
     {
         $result = Service::urlEncode($text);
         self::assertSame($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/Web/WebServiceTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/Web/WebServiceTest.php
index f37bbd3464..a5ef6e6cd4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/Web/WebServiceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/Web/WebServiceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation\Functions\Web;
 
 use PhpOffice\PhpSpreadsheet\Settings;
diff --git a/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
index 0e0323a60b..9385a1a950 100644
--- a/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/FunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -8,15 +10,9 @@
 
 class FunctionsTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
-    /**
-     * @var string
-     */
-    private $returnDate;
+    private string $returnDate;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php b/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php
index 5e9944e939..efaefc9a04 100644
--- a/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/MergedCellTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
@@ -11,11 +13,9 @@
 class MergedCellTest extends TestCase
 {
     /**
-     * @param mixed $expectedResult
-     *
      * @dataProvider providerWorksheetFormulaeColumns
      */
-    public function testMergedCellColumns(string $formula, $expectedResult): void
+    public function testMergedCellColumns(string $formula, mixed $expectedResult): void
     {
         $spreadSheet = new Spreadsheet();
 
@@ -53,11 +53,9 @@ public static function providerWorksheetFormulaeColumns(): array
     }
 
     /**
-     * @param mixed $expectedResult
-     *
      * @dataProvider providerWorksheetFormulaeRows
      */
-    public function testMergedCellRows(string $formula, $expectedResult): void
+    public function testMergedCellRows(string $formula, mixed $expectedResult): void
     {
         $spreadSheet = new Spreadsheet();
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/NullEqualsZeroTest.php b/tests/PhpSpreadsheetTests/Calculation/NullEqualsZeroTest.php
index 0168e080d4..c9b8409c28 100644
--- a/tests/PhpSpreadsheetTests/Calculation/NullEqualsZeroTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/NullEqualsZeroTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Calculation/ParseFormulaTest.php b/tests/PhpSpreadsheetTests/Calculation/ParseFormulaTest.php
index 06601abc0d..c4958b5a92 100644
--- a/tests/PhpSpreadsheetTests/Calculation/ParseFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/ParseFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Calculation/RefErrorTest.php b/tests/PhpSpreadsheetTests/Calculation/RefErrorTest.php
index e9f45104c6..657d79fbb5 100644
--- a/tests/PhpSpreadsheetTests/Calculation/RefErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/RefErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -8,11 +10,9 @@
 class RefErrorTest extends TestCase
 {
     /**
-     * @param mixed $expected
-     *
      * @dataProvider providerRefError
      */
-    public function testRefError($expected, string $formula): void
+    public function testRefError(mixed $expected, string $formula): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet1 = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Calculation/RowColumnReferenceTest.php b/tests/PhpSpreadsheetTests/Calculation/RowColumnReferenceTest.php
index 1c28334bd8..1219583643 100644
--- a/tests/PhpSpreadsheetTests/Calculation/RowColumnReferenceTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/RowColumnReferenceTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Calculation/StringLengthTest.php b/tests/PhpSpreadsheetTests/Calculation/StringLengthTest.php
index 09f3211884..33081e9aa6 100644
--- a/tests/PhpSpreadsheetTests/Calculation/StringLengthTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/StringLengthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Calculation/StructuredReferenceFormulaTest.php b/tests/PhpSpreadsheetTests/Calculation/StructuredReferenceFormulaTest.php
index 8d7977d431..b20c0985db 100644
--- a/tests/PhpSpreadsheetTests/Calculation/StructuredReferenceFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/StructuredReferenceFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/PhpSpreadsheetTests/Calculation/TranslationTest.php b/tests/PhpSpreadsheetTests/Calculation/TranslationTest.php
index d01dde7eab..c14ee0a64a 100644
--- a/tests/PhpSpreadsheetTests/Calculation/TranslationTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/TranslationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
@@ -9,18 +11,11 @@
 
 class TranslationTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
-    /**
-     * @var string
-     */
-    private $returnDate;
+    private string $returnDate;
 
-    /** @var string */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Calculation/XlfnFunctionsTest.php b/tests/PhpSpreadsheetTests/Calculation/XlfnFunctionsTest.php
index 3edd22c871..73d1af3cc1 100644
--- a/tests/PhpSpreadsheetTests/Calculation/XlfnFunctionsTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/XlfnFunctionsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Calculation;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Cell/AddressHelperTest.php b/tests/PhpSpreadsheetTests/Cell/AddressHelperTest.php
index 8ac5acc5e7..7b41d8bd2d 100644
--- a/tests/PhpSpreadsheetTests/Cell/AddressHelperTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/AddressHelperTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\AddressHelper;
diff --git a/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php b/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php
index cb60213e7a..9963f01f6c 100644
--- a/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\AdvancedValueBinder;
@@ -92,14 +94,8 @@ public function testBooleanLocale(): void
 
     /**
      * @dataProvider currencyProvider
-     *
-     * @param mixed $value
-     * @param mixed $valueBinded
-     * @param mixed $thousandsSeparator
-     * @param mixed $decimalSeparator
-     * @param mixed $currencyCode
      */
-    public function testCurrency($value, $valueBinded, $thousandsSeparator, $decimalSeparator, $currencyCode): void
+    public function testCurrency(mixed $value, mixed $valueBinded, mixed $thousandsSeparator, mixed $decimalSeparator, mixed $currencyCode): void
     {
         StringHelper::setCurrencyCode($currencyCode);
         StringHelper::setDecimalSeparator($decimalSeparator);
@@ -135,11 +131,8 @@ public static function currencyProvider(): array
 
     /**
      * @dataProvider fractionProvider
-     *
-     * @param mixed $value
-     * @param mixed $valueBinded
      */
-    public function testFractions($value, $valueBinded): void
+    public function testFractions(mixed $value, mixed $valueBinded): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
@@ -171,11 +164,8 @@ public static function fractionProvider(): array
 
     /**
      * @dataProvider percentageProvider
-     *
-     * @param mixed $value
-     * @param mixed $valueBinded
      */
-    public function testPercentages($value, $valueBinded): void
+    public function testPercentages(mixed $value, mixed $valueBinded): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
@@ -201,11 +191,8 @@ public static function percentageProvider(): array
 
     /**
      * @dataProvider timeProvider
-     *
-     * @param mixed $value
-     * @param mixed $valueBinded
      */
-    public function testTimes($value, $valueBinded): void
+    public function testTimes(mixed $value, mixed $valueBinded): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Cell/CellAddressTest.php b/tests/PhpSpreadsheetTests/Cell/CellAddressTest.php
index eb8e68027d..2cddc48a06 100644
--- a/tests/PhpSpreadsheetTests/Cell/CellAddressTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/CellAddressTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\CellAddress;
@@ -38,10 +40,8 @@ public static function providerCreateFromCellAddress(): array
 
     /**
      * @dataProvider providerCreateFromCellAddressException
-     *
-     * @param mixed $cellAddress
      */
-    public function testCreateFromCellAddressException($cellAddress): void
+    public function testCreateFromCellAddressException(mixed $cellAddress): void
     {
         $this->expectException(Exception::class);
         $this->expectExceptionMessage(
@@ -84,11 +84,8 @@ public function testCreateFromColumnAndRow(
 
     /**
      * @dataProvider providerCreateFromColumnRowException
-     *
-     * @param mixed $columnId
-     * @param mixed $rowId
      */
-    public function testCreateFromColumnRowException($columnId, $rowId): void
+    public function testCreateFromColumnRowException(mixed $columnId, mixed $rowId): void
     {
         $this->expectException(Exception::class);
         $this->expectExceptionMessage('Row and Column Ids must be positive integer values');
@@ -135,11 +132,8 @@ public static function providerCreateFromColumnRowArray(): array
 
     /**
      * @dataProvider providerCreateFromColumnRowException
-     *
-     * @param mixed $columnId
-     * @param mixed $rowId
      */
-    public function testCreateFromColumnRowArrayException($columnId, $rowId): void
+    public function testCreateFromColumnRowArrayException(mixed $columnId, mixed $rowId): void
     {
         $this->expectException(Exception::class);
         $this->expectExceptionMessage('Row and Column Ids must be positive integer values');
diff --git a/tests/PhpSpreadsheetTests/Cell/CellDetachTest.php b/tests/PhpSpreadsheetTests/Cell/CellDetachTest.php
index 950322a7f9..388d3ad713 100644
--- a/tests/PhpSpreadsheetTests/Cell/CellDetachTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/CellDetachTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
diff --git a/tests/PhpSpreadsheetTests/Cell/CellRangeTest.php b/tests/PhpSpreadsheetTests/Cell/CellRangeTest.php
index 1557a69827..8c8923ab36 100644
--- a/tests/PhpSpreadsheetTests/Cell/CellRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/CellRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\CellAddress;
diff --git a/tests/PhpSpreadsheetTests/Cell/CellTest.php b/tests/PhpSpreadsheetTests/Cell/CellTest.php
index ef5f28eb75..fee24c78c5 100644
--- a/tests/PhpSpreadsheetTests/Cell/CellTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/CellTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\AdvancedValueBinder;
@@ -72,11 +74,8 @@ public function testSetValueBinderOverride2(): void
 
     /**
      * @dataProvider providerSetValueExplicit
-     *
-     * @param mixed $expected
-     * @param mixed $value
      */
-    public function testSetValueExplicit($expected, $value, string $dataType): void
+    public function testSetValueExplicit(mixed $expected, mixed $value, string $dataType): void
     {
         $spreadsheet = new Spreadsheet();
         $cell = $spreadsheet->getActiveSheet()->getCell('A1');
@@ -106,10 +105,8 @@ public function testInvalidIsoDateSetValueExplicit(): void
 
     /**
      * @dataProvider providerSetValueExplicitException
-     *
-     * @param mixed $value
      */
-    public function testSetValueExplicitException($value, string $dataType): void
+    public function testSetValueExplicitException(mixed $value, string $dataType): void
     {
         $this->expectException(Exception::class);
 
diff --git a/tests/PhpSpreadsheetTests/Cell/ColumnRangeTest.php b/tests/PhpSpreadsheetTests/Cell/ColumnRangeTest.php
index 14455701fd..10da1dd21c 100644
--- a/tests/PhpSpreadsheetTests/Cell/ColumnRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/ColumnRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\ColumnRange;
diff --git a/tests/PhpSpreadsheetTests/Cell/CoordinateTest.php b/tests/PhpSpreadsheetTests/Cell/CoordinateTest.php
index 62eeba1a0c..c67145b25e 100644
--- a/tests/PhpSpreadsheetTests/Cell/CoordinateTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/CoordinateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\Coordinate;
@@ -11,11 +13,8 @@ class CoordinateTest extends TestCase
 {
     /**
      * @dataProvider providerColumnString
-     *
-     * @param mixed $expectedResult
-     * @param mixed $string
      */
-    public function testColumnIndexFromString($expectedResult, $string): void
+    public function testColumnIndexFromString(mixed $expectedResult, mixed $string): void
     {
         $columnIndex = Coordinate::columnIndexFromString($string);
         self::assertEquals($expectedResult, $columnIndex);
@@ -61,11 +60,8 @@ public function testColumnIndexFromStringTooShort(): void
 
     /**
      * @dataProvider providerColumnIndex
-     *
-     * @param mixed $expectedResult
-     * @param int $columnIndex
      */
-    public function testStringFromColumnIndex($expectedResult, $columnIndex): void
+    public function testStringFromColumnIndex(mixed $expectedResult, int $columnIndex): void
     {
         $string = Coordinate::stringFromColumnIndex($columnIndex);
         self::assertEquals($expectedResult, $string);
@@ -81,11 +77,8 @@ public static function providerColumnIndex(): array
 
     /**
      * @dataProvider providerCoordinates
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testCoordinateFromString($expectedResult, $rangeSet): void
+    public function testCoordinateFromString(mixed $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::coordinateFromString($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -157,11 +150,8 @@ public function testCoordinateFromStringWithInvalidAddress(): void
 
     /**
      * @dataProvider providerAbsoluteCoordinates
-     *
-     * @param string $expectedResult
-     * @param string $rangeSet
      */
-    public function testAbsoluteCoordinateFromString($expectedResult, $rangeSet): void
+    public function testAbsoluteCoordinateFromString(string $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::absoluteCoordinate($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -189,11 +179,8 @@ public function testAbsoluteCoordinateFromStringWithRangeAddress(): void
 
     /**
      * @dataProvider providerAbsoluteReferences
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testAbsoluteReferenceFromString($expectedResult, $rangeSet): void
+    public function testAbsoluteReferenceFromString(mixed $expectedResult, mixed $rangeSet): void
     {
         $result = Coordinate::absoluteReference($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -221,11 +208,8 @@ public function testAbsoluteReferenceFromStringWithRangeAddress(): void
 
     /**
      * @dataProvider providerSplitRange
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testSplitRange($expectedResult, $rangeSet): void
+    public function testSplitRange(mixed $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::splitRange($rangeSet);
         foreach ($result as $key => $split) {
@@ -244,11 +228,8 @@ public static function providerSplitRange(): array
 
     /**
      * @dataProvider providerBuildRange
-     *
-     * @param mixed $expectedResult
-     * @param mixed $rangeSets
      */
-    public function testBuildRange($expectedResult, $rangeSets): void
+    public function testBuildRange(mixed $expectedResult, mixed $rangeSets): void
     {
         $result = Coordinate::buildRange($rangeSets);
         self::assertEquals($expectedResult, $result);
@@ -279,11 +260,8 @@ public function testBuildRangeInvalid2(): void
 
     /**
      * @dataProvider providerRangeBoundaries
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testRangeBoundaries($expectedResult, $rangeSet): void
+    public function testRangeBoundaries(mixed $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::rangeBoundaries($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -296,11 +274,8 @@ public static function providerRangeBoundaries(): array
 
     /**
      * @dataProvider providerRangeDimension
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testRangeDimension($expectedResult, $rangeSet): void
+    public function testRangeDimension(mixed $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::rangeDimension($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -313,11 +288,8 @@ public static function providerRangeDimension(): array
 
     /**
      * @dataProvider providerGetRangeBoundaries
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testGetRangeBoundaries($expectedResult, $rangeSet): void
+    public function testGetRangeBoundaries(mixed $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::getRangeBoundaries($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -330,11 +302,8 @@ public static function providerGetRangeBoundaries(): array
 
     /**
      * @dataProvider providerExtractAllCellReferencesInRange
-     *
-     * @param array $expectedResult
-     * @param string $rangeSet
      */
-    public function testExtractAllCellReferencesInRange($expectedResult, $rangeSet): void
+    public function testExtractAllCellReferencesInRange(array $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::extractAllCellReferencesInRange($rangeSet);
         self::assertEquals($expectedResult, $result);
@@ -347,10 +316,8 @@ public static function providerExtractAllCellReferencesInRange(): array
 
     /**
      * @dataProvider providerInvalidRange
-     *
-     * @param string $range
      */
-    public function testExtractAllCellReferencesInRangeInvalidRange($range): void
+    public function testExtractAllCellReferencesInRangeInvalidRange(string $range): void
     {
         $this->expectException(Exception::class);
         $this->expectExceptionMessage('Invalid range: "' . $range . '"');
@@ -365,11 +332,8 @@ public static function providerInvalidRange(): array
 
     /**
      * @dataProvider providerMergeRangesInCollection
-     *
-     * @param mixed $expectedResult
-     * @param mixed $rangeSets
      */
-    public function testMergeRangesInCollection($expectedResult, $rangeSets): void
+    public function testMergeRangesInCollection(mixed $expectedResult, mixed $rangeSets): void
     {
         $result = Coordinate::mergeRangesInCollection($rangeSets);
         self::assertEquals($expectedResult, $result);
@@ -382,11 +346,8 @@ public static function providerMergeRangesInCollection(): array
 
     /**
      * @dataProvider providerCoordinateIsRange
-     *
-     * @param mixed $expectedResult
-     * @param string $rangeSet
      */
-    public function testCoordinateIsRange($expectedResult, $rangeSet): void
+    public function testCoordinateIsRange(mixed $expectedResult, string $rangeSet): void
     {
         $result = Coordinate::coordinateIsRange($rangeSet);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php b/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php
index 176dd6acaf..974297c4ce 100644
--- a/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/DataTypeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
@@ -34,12 +36,7 @@ public function testCheckString(): void
         self::assertSame($expected, $result3);
     }
 
-    /**
-     * @param int $length
-     *
-     * @return string
-     */
-    private function randr($length = 8)
+    private function randr(int $length = 8): string
     {
         $string = '';
         for ($i = 0; $i < $length; ++$i) {
diff --git a/tests/PhpSpreadsheetTests/Cell/DataValidationTest.php b/tests/PhpSpreadsheetTests/Cell/DataValidationTest.php
index 62be68dd26..cad9e6de8e 100644
--- a/tests/PhpSpreadsheetTests/Cell/DataValidationTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/DataValidationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Cell/DataValidator2Test.php b/tests/PhpSpreadsheetTests/Cell/DataValidator2Test.php
index 9153a5b811..f16191a0fc 100644
--- a/tests/PhpSpreadsheetTests/Cell/DataValidator2Test.php
+++ b/tests/PhpSpreadsheetTests/Cell/DataValidator2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Cell/DataValidatorTest.php b/tests/PhpSpreadsheetTests/Cell/DataValidatorTest.php
index bae315affc..6792197101 100644
--- a/tests/PhpSpreadsheetTests/Cell/DataValidatorTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/DataValidatorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php b/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php
index 426ce8cf6d..9057c2a315 100644
--- a/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/DefaultValueBinderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use DateTime;
@@ -14,10 +16,8 @@ class DefaultValueBinderTest extends TestCase
 {
     /**
      * @dataProvider binderProvider
-     *
-     * @param mixed $value
      */
-    public function testBindValue($value): void
+    public function testBindValue(null|string|bool|int|float|DateTime|DateTimeImmutable $value): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
@@ -50,11 +50,8 @@ public static function binderProvider(): array
 
     /**
      * @dataProvider providerDataTypeForValue
-     *
-     * @param mixed $expectedResult
-     * @param mixed $value
      */
-    public function testDataTypeForValue($expectedResult, $value): void
+    public function testDataTypeForValue(mixed $expectedResult, mixed $value): void
     {
         $result = DefaultValueBinder::dataTypeForValue($value);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php b/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php
index e92fbaf3d7..68d43e418c 100644
--- a/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/HyperlinkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\Hyperlink;
diff --git a/tests/PhpSpreadsheetTests/Cell/RowRangeTest.php b/tests/PhpSpreadsheetTests/Cell/RowRangeTest.php
index 32605cf070..52fd357f51 100644
--- a/tests/PhpSpreadsheetTests/Cell/RowRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/RowRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\RowRange;
diff --git a/tests/PhpSpreadsheetTests/Cell/StringValueBinderTest.php b/tests/PhpSpreadsheetTests/Cell/StringValueBinderTest.php
index 3ebc09d7d9..19a08ac4d2 100644
--- a/tests/PhpSpreadsheetTests/Cell/StringValueBinderTest.php
+++ b/tests/PhpSpreadsheetTests/Cell/StringValueBinderTest.php
@@ -1,12 +1,13 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use DateTime;
 use DateTimeZone;
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
-use PhpOffice\PhpSpreadsheet\Cell\IValueBinder;
 use PhpOffice\PhpSpreadsheet\Cell\StringValueBinder;
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -14,10 +15,7 @@
 
 class StringValueBinderTest extends TestCase
 {
-    /**
-     * @var IValueBinder
-     */
-    private $valueBinder;
+    private \PhpOffice\PhpSpreadsheet\Cell\IValueBinder $valueBinder;
 
     protected function setUp(): void
     {
@@ -31,13 +29,10 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerDataValuesDefault
-     *
-     * @param mixed $value
-     * @param mixed $expectedValue
      */
     public function testStringValueBinderDefaultBehaviour(
-        $value,
-        $expectedValue,
+        mixed $value,
+        mixed $expectedValue,
         string $expectedDataType
     ): void {
         Cell::setValueBinder(new StringValueBinder());
@@ -80,13 +75,10 @@ public static function providerDataValuesDefault(): array
 
     /**
      * @dataProvider providerDataValuesSuppressNullConversion
-     *
-     * @param mixed $value
-     * @param mixed $expectedValue
      */
     public function testStringValueBinderSuppressNullConversion(
-        $value,
-        $expectedValue,
+        mixed $value,
+        mixed $expectedValue,
         string $expectedDataType
     ): void {
         $binder = new StringValueBinder();
@@ -112,13 +104,10 @@ public static function providerDataValuesSuppressNullConversion(): array
 
     /**
      * @dataProvider providerDataValuesSuppressBooleanConversion
-     *
-     * @param mixed $value
-     * @param mixed $expectedValue
      */
     public function testStringValueBinderSuppressBooleanConversion(
-        $value,
-        $expectedValue,
+        mixed $value,
+        mixed $expectedValue,
         string $expectedDataType
     ): void {
         $binder = new StringValueBinder();
@@ -145,13 +134,10 @@ public static function providerDataValuesSuppressBooleanConversion(): array
 
     /**
      * @dataProvider providerDataValuesSuppressNumericConversion
-     *
-     * @param mixed $value
-     * @param mixed $expectedValue
      */
     public function testStringValueBinderSuppressNumericConversion(
-        $value,
-        $expectedValue,
+        mixed $value,
+        mixed $expectedValue,
         string $expectedDataType
     ): void {
         $binder = new StringValueBinder();
@@ -185,13 +171,10 @@ public static function providerDataValuesSuppressNumericConversion(): array
 
     /**
      * @dataProvider providerDataValuesSuppressFormulaConversion
-     *
-     * @param mixed $value
-     * @param mixed $expectedValue
      */
     public function testStringValueBinderSuppressFormulaConversion(
-        $value,
-        $expectedValue,
+        mixed $value,
+        mixed $expectedValue,
         string $expectedDataType
     ): void {
         $binder = new StringValueBinder();
@@ -215,13 +198,10 @@ public static function providerDataValuesSuppressFormulaConversion(): array
 
     /**
      * @dataProvider providerDataValuesSuppressAllConversion
-     *
-     * @param mixed $value
-     * @param mixed $expectedValue
      */
     public function testStringValueBinderSuppressAllConversion(
-        $value,
-        $expectedValue,
+        mixed $value,
+        mixed $expectedValue,
         string $expectedDataType
     ): void {
         $binder = new StringValueBinder();
diff --git a/tests/PhpSpreadsheetTests/Cell/ValueBinderWithOverriddenDataTypeForValue.php b/tests/PhpSpreadsheetTests/Cell/ValueBinderWithOverriddenDataTypeForValue.php
index e2ddc60234..ea4610e917 100644
--- a/tests/PhpSpreadsheetTests/Cell/ValueBinderWithOverriddenDataTypeForValue.php
+++ b/tests/PhpSpreadsheetTests/Cell/ValueBinderWithOverriddenDataTypeForValue.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Cell;
 
 use PhpOffice\PhpSpreadsheet\Cell\DefaultValueBinder;
diff --git a/tests/PhpSpreadsheetTests/CellReferenceHelperTest.php b/tests/PhpSpreadsheetTests/CellReferenceHelperTest.php
index 8431a800f9..572ffbff06 100644
--- a/tests/PhpSpreadsheetTests/CellReferenceHelperTest.php
+++ b/tests/PhpSpreadsheetTests/CellReferenceHelperTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\CellReferenceHelper;
diff --git a/tests/PhpSpreadsheetTests/Chart/AxisGlowTest.php b/tests/PhpSpreadsheetTests/Chart/AxisGlowTest.php
index b14d63fb7c..2d42a44409 100644
--- a/tests/PhpSpreadsheetTests/Chart/AxisGlowTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/AxisGlowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/AxisPropertiesTest.php b/tests/PhpSpreadsheetTests/Chart/AxisPropertiesTest.php
index 59eaf494da..11c11660e7 100644
--- a/tests/PhpSpreadsheetTests/Chart/AxisPropertiesTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/AxisPropertiesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/AxisShadowTest.php b/tests/PhpSpreadsheetTests/Chart/AxisShadowTest.php
index 78deece481..5a9b43265b 100644
--- a/tests/PhpSpreadsheetTests/Chart/AxisShadowTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/AxisShadowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/BarChartCustomColorsTest.php b/tests/PhpSpreadsheetTests/Chart/BarChartCustomColorsTest.php
index 431ad670c5..24fd0b0daf 100644
--- a/tests/PhpSpreadsheetTests/Chart/BarChartCustomColorsTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/BarChartCustomColorsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/ChartBorderTest.php b/tests/PhpSpreadsheetTests/Chart/ChartBorderTest.php
index f5efc09f9a..834c89c4a5 100644
--- a/tests/PhpSpreadsheetTests/Chart/ChartBorderTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/ChartBorderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Properties;
diff --git a/tests/PhpSpreadsheetTests/Chart/ChartMethodTest.php b/tests/PhpSpreadsheetTests/Chart/ChartMethodTest.php
index 5c3622ad46..a7ff421b3e 100644
--- a/tests/PhpSpreadsheetTests/Chart/ChartMethodTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/ChartMethodTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32CatAxValAxTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32CatAxValAxTest.php
index 458e8f2727..083e9a6c3d 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32CatAxValAxTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32CatAxValAxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32ColoredAxisLabelTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32ColoredAxisLabelTest.php
index f0c84bf0b3..ec705f6ca6 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32ColoredAxisLabelTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32ColoredAxisLabelTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32DsvGlowTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32DsvGlowTest.php
index 26ef34ee1b..64e559d7d2 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32DsvGlowTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32DsvGlowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32DsvLabelsTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32DsvLabelsTest.php
index b64907765b..b53be9047a 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32DsvLabelsTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32DsvLabelsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php
index fcde7ae359..21999037cc 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\ChartColor;
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32XmlTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32XmlTest.php
index e478b0f5c2..d6b6564a0a 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32XmlTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32XmlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Properties;
diff --git a/tests/PhpSpreadsheetTests/Chart/ChartsOpenpyxlTest.php b/tests/PhpSpreadsheetTests/Chart/ChartsOpenpyxlTest.php
index e6f574fd3c..706784185e 100644
--- a/tests/PhpSpreadsheetTests/Chart/ChartsOpenpyxlTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/ChartsOpenpyxlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/ChartsTitleTest.php b/tests/PhpSpreadsheetTests/Chart/ChartsTitleTest.php
index 5a929c6285..ff6b6a1ea0 100644
--- a/tests/PhpSpreadsheetTests/Chart/ChartsTitleTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/ChartsTitleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Title;
diff --git a/tests/PhpSpreadsheetTests/Chart/ColorTest.php b/tests/PhpSpreadsheetTests/Chart/ColorTest.php
index e8326e5237..62da8ef3a4 100644
--- a/tests/PhpSpreadsheetTests/Chart/ColorTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/ColorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\ChartColor;
diff --git a/tests/PhpSpreadsheetTests/Chart/DataSeriesColorTest.php b/tests/PhpSpreadsheetTests/Chart/DataSeriesColorTest.php
index c0b7069d87..690445d3e4 100644
--- a/tests/PhpSpreadsheetTests/Chart/DataSeriesColorTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/DataSeriesColorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis as ChartAxis;
diff --git a/tests/PhpSpreadsheetTests/Chart/DataSeriesValues2Test.php b/tests/PhpSpreadsheetTests/Chart/DataSeriesValues2Test.php
index bba1c1f1b3..a525322b21 100644
--- a/tests/PhpSpreadsheetTests/Chart/DataSeriesValues2Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/DataSeriesValues2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php b/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php
index 47c2fb8956..58783bc1d3 100644
--- a/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/DataSeriesValuesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\DataSeriesValues;
diff --git a/tests/PhpSpreadsheetTests/Chart/GridlinesLineStyleTest.php b/tests/PhpSpreadsheetTests/Chart/GridlinesLineStyleTest.php
index 49adf3cee1..f4e0115395 100644
--- a/tests/PhpSpreadsheetTests/Chart/GridlinesLineStyleTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/GridlinesLineStyleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/GridlinesShadowGlowTest.php b/tests/PhpSpreadsheetTests/Chart/GridlinesShadowGlowTest.php
index e12154413e..908190bcb8 100644
--- a/tests/PhpSpreadsheetTests/Chart/GridlinesShadowGlowTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/GridlinesShadowGlowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/Issue2077Test.php b/tests/PhpSpreadsheetTests/Chart/Issue2077Test.php
index 2d1688c6b9..520af8c27a 100644
--- a/tests/PhpSpreadsheetTests/Chart/Issue2077Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/Issue2077Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/Issue2506Test.php b/tests/PhpSpreadsheetTests/Chart/Issue2506Test.php
index e1c3077098..32a8fcee7c 100644
--- a/tests/PhpSpreadsheetTests/Chart/Issue2506Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/Issue2506Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/Issue2931Test.php b/tests/PhpSpreadsheetTests/Chart/Issue2931Test.php
index 960eb04e80..2e1bd9d81e 100644
--- a/tests/PhpSpreadsheetTests/Chart/Issue2931Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/Issue2931Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/Issue2965Test.php b/tests/PhpSpreadsheetTests/Chart/Issue2965Test.php
index 8294d39b68..90396e27f7 100644
--- a/tests/PhpSpreadsheetTests/Chart/Issue2965Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/Issue2965Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/Issue3397Test.php b/tests/PhpSpreadsheetTests/Chart/Issue3397Test.php
index 85670976e3..06b8189f48 100644
--- a/tests/PhpSpreadsheetTests/Chart/Issue3397Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/Issue3397Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/Issue589Test.php b/tests/PhpSpreadsheetTests/Chart/Issue589Test.php
index 68747f6c58..7d1879ee25 100644
--- a/tests/PhpSpreadsheetTests/Chart/Issue589Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/Issue589Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use DOMDocument;
@@ -21,7 +23,7 @@ class Issue589Test extends TestCase
      *
      * @param string|string[] $color HEX color or array with HEX colors
      */
-    private function buildChartSpreadsheet($color): Spreadsheet
+    private function buildChartSpreadsheet(string|array $color): Spreadsheet
     {
         // Problem occurs when setting plot line color
         // The output chart xml file is missing the a:ln tag
diff --git a/tests/PhpSpreadsheetTests/Chart/LayoutEffectsTest.php b/tests/PhpSpreadsheetTests/Chart/LayoutEffectsTest.php
index 4c1bb9e5dd..ca8070ae38 100644
--- a/tests/PhpSpreadsheetTests/Chart/LayoutEffectsTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LayoutEffectsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/LayoutTest.php b/tests/PhpSpreadsheetTests/Chart/LayoutTest.php
index 5df139e3e5..e54f1646ba 100644
--- a/tests/PhpSpreadsheetTests/Chart/LayoutTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LayoutTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\ChartColor;
diff --git a/tests/PhpSpreadsheetTests/Chart/LegendColorTest.php b/tests/PhpSpreadsheetTests/Chart/LegendColorTest.php
index 1bf5cb32e0..7393aa7e60 100644
--- a/tests/PhpSpreadsheetTests/Chart/LegendColorTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LegendColorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\AxisText;
diff --git a/tests/PhpSpreadsheetTests/Chart/LegendTest.php b/tests/PhpSpreadsheetTests/Chart/LegendTest.php
index e68145c075..7c4cdddfdf 100644
--- a/tests/PhpSpreadsheetTests/Chart/LegendTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LegendTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Legend;
diff --git a/tests/PhpSpreadsheetTests/Chart/LineStylesTest.php b/tests/PhpSpreadsheetTests/Chart/LineStylesTest.php
index ef940c994a..b382c4a929 100644
--- a/tests/PhpSpreadsheetTests/Chart/LineStylesTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/LineStylesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\GridLines;
diff --git a/tests/PhpSpreadsheetTests/Chart/MultiplierTest.php b/tests/PhpSpreadsheetTests/Chart/MultiplierTest.php
index c819e4733b..72a02d5ad0 100644
--- a/tests/PhpSpreadsheetTests/Chart/MultiplierTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/MultiplierTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/PR3163Test.php b/tests/PhpSpreadsheetTests/Chart/PR3163Test.php
index 154bc18da8..bfce4ca8d5 100644
--- a/tests/PhpSpreadsheetTests/Chart/PR3163Test.php
+++ b/tests/PhpSpreadsheetTests/Chart/PR3163Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/PieFillTest.php b/tests/PhpSpreadsheetTests/Chart/PieFillTest.php
index 5b35ca3d2e..7a501efb01 100644
--- a/tests/PhpSpreadsheetTests/Chart/PieFillTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/PieFillTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/RenderTest.php b/tests/PhpSpreadsheetTests/Chart/RenderTest.php
index b10e854f95..fe1a0c1eb2 100644
--- a/tests/PhpSpreadsheetTests/Chart/RenderTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/RenderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Chart;
diff --git a/tests/PhpSpreadsheetTests/Chart/RoundedCornersTest.php b/tests/PhpSpreadsheetTests/Chart/RoundedCornersTest.php
index 93bbaa231c..8796451dc8 100644
--- a/tests/PhpSpreadsheetTests/Chart/RoundedCornersTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/RoundedCornersTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Chart/ShadowPresetsTest.php b/tests/PhpSpreadsheetTests/Chart/ShadowPresetsTest.php
index 20cacbc173..5da26502cd 100644
--- a/tests/PhpSpreadsheetTests/Chart/ShadowPresetsTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/ShadowPresetsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Axis;
diff --git a/tests/PhpSpreadsheetTests/Chart/TitleTest.php b/tests/PhpSpreadsheetTests/Chart/TitleTest.php
index 4c01d5fec2..6d1507acd4 100644
--- a/tests/PhpSpreadsheetTests/Chart/TitleTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/TitleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Chart\Title;
diff --git a/tests/PhpSpreadsheetTests/Chart/TrendLineTest.php b/tests/PhpSpreadsheetTests/Chart/TrendLineTest.php
index 954a733688..59c01d395a 100644
--- a/tests/PhpSpreadsheetTests/Chart/TrendLineTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/TrendLineTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Chart;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Collection/CellsTest.php b/tests/PhpSpreadsheetTests/Collection/CellsTest.php
index 9a59458ae7..46f8755e0b 100644
--- a/tests/PhpSpreadsheetTests/Collection/CellsTest.php
+++ b/tests/PhpSpreadsheetTests/Collection/CellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Collection;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
diff --git a/tests/PhpSpreadsheetTests/CommentTest.php b/tests/PhpSpreadsheetTests/CommentTest.php
index f2e0c2993c..86a8825d6a 100644
--- a/tests/PhpSpreadsheetTests/CommentTest.php
+++ b/tests/PhpSpreadsheetTests/CommentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Comment;
diff --git a/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php b/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php
index 0341041279..73c98afe2d 100644
--- a/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php
+++ b/tests/PhpSpreadsheetTests/Custom/ComplexAssert.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Custom;
 
 use Complex\Complex;
@@ -7,10 +9,7 @@
 
 class ComplexAssert extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $errorMessage = '';
+    private string $errorMessage = '';
 
     /** @var float */
     private $delta = 0.0;
@@ -20,11 +19,7 @@ public function __construct()
         parent::__construct('complexAssert');
     }
 
-    /**
-     * @param mixed $expected
-     * @param mixed $actual
-     */
-    private function testExpectedExceptions($expected, $actual): bool
+    private function testExpectedExceptions(string|float $expected, string|float $actual): bool
     {
         //    Expecting an error, so we do a straight string comparison
         if ($expected === $actual) {
@@ -56,11 +51,7 @@ public function setDelta(float $delta): self
         return $this;
     }
 
-    /**
-     * @param mixed $expected
-     * @param mixed $actual
-     */
-    public function assertComplexEquals($expected, $actual, ?float $delta = null): bool
+    public function assertComplexEquals(mixed $expected, mixed $actual, ?float $delta = null): bool
     {
         if ($expected === INF || (is_string($expected) && $expected[0] === '#')) {
             return $this->testExpectedExceptions($expected, $actual);
@@ -100,11 +91,7 @@ public function getErrorMessage(): string
         return $this->errorMessage;
     }
 
-    /**
-     * @param mixed $expected
-     * @param mixed $actual
-     */
-    public function runAssertComplexEquals($expected, $actual, ?float $delta = null): void
+    public function runAssertComplexEquals(mixed $expected, mixed $actual, ?float $delta = null): void
     {
         self::assertTrue($this->assertComplexEquals($expected, $actual, $delta), $this->getErrorMessage());
     }
diff --git a/tests/PhpSpreadsheetTests/DefinedNameFormulaTest.php b/tests/PhpSpreadsheetTests/DefinedNameFormulaTest.php
index e1a9c2e696..131163def6 100644
--- a/tests/PhpSpreadsheetTests/DefinedNameFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/DefinedNameFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\DefinedName;
diff --git a/tests/PhpSpreadsheetTests/DefinedNameTest.php b/tests/PhpSpreadsheetTests/DefinedNameTest.php
index c001f204e7..75b559be08 100644
--- a/tests/PhpSpreadsheetTests/DefinedNameTest.php
+++ b/tests/PhpSpreadsheetTests/DefinedNameTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\DefinedName;
@@ -10,8 +12,7 @@
 
 class DefinedNameTest extends TestCase
 {
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private \PhpOffice\PhpSpreadsheet\Spreadsheet $spreadsheet;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Document/EpochTest.php b/tests/PhpSpreadsheetTests/Document/EpochTest.php
index d9a0e1efe7..feb98c8af9 100644
--- a/tests/PhpSpreadsheetTests/Document/EpochTest.php
+++ b/tests/PhpSpreadsheetTests/Document/EpochTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Document;
 
 use DateTime;
diff --git a/tests/PhpSpreadsheetTests/Document/PropertiesTest.php b/tests/PhpSpreadsheetTests/Document/PropertiesTest.php
index 56931b392e..12de9c1220 100644
--- a/tests/PhpSpreadsheetTests/Document/PropertiesTest.php
+++ b/tests/PhpSpreadsheetTests/Document/PropertiesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Document;
 
 use DateTime;
@@ -48,11 +50,8 @@ public function testSetCreator(): void
 
     /**
      * @dataProvider providerCreationTime
-     *
-     * @param mixed $expectedCreationTime
-     * @param mixed $created
      */
-    public function testSetCreated($expectedCreationTime, $created): void
+    public function testSetCreated(mixed $expectedCreationTime, mixed $created): void
     {
         $expectedCreationTime = $expectedCreationTime ?? $this->startTime;
 
@@ -80,11 +79,8 @@ public function testSetModifier(): void
 
     /**
      * @dataProvider providerModifiedTime
-     *
-     * @param mixed $expectedModifiedTime
-     * @param mixed $modified
      */
-    public function testSetModified($expectedModifiedTime, $modified): void
+    public function testSetModified(mixed $expectedModifiedTime, mixed $modified): void
     {
         $expectedModifiedTime = $expectedModifiedTime ?? $this->startTime;
 
@@ -160,14 +156,8 @@ public function testSetManager(): void
 
     /**
      * @dataProvider providerCustomProperties
-     *
-     * @param mixed $expectedType
-     * @param mixed $expectedValue
-     * @param string $propertyName
-     * @param mixed $propertyValue
-     * @param ?string $propertyType
      */
-    public function testSetCustomProperties($expectedType, $expectedValue, $propertyName, $propertyValue, $propertyType = null): void
+    public function testSetCustomProperties(mixed $expectedType, mixed $expectedValue, string $propertyName, mixed $propertyValue, ?string $propertyType = null): void
     {
         if ($propertyType === null) {
             $this->properties->setCustomProperty($propertyName, $propertyValue);
diff --git a/tests/PhpSpreadsheetTests/Document/SecurityTest.php b/tests/PhpSpreadsheetTests/Document/SecurityTest.php
index 9599626030..015e32ba29 100644
--- a/tests/PhpSpreadsheetTests/Document/SecurityTest.php
+++ b/tests/PhpSpreadsheetTests/Document/SecurityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Document;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/DocumentGeneratorTest.php b/tests/PhpSpreadsheetTests/DocumentGeneratorTest.php
index 20d023ea7f..ef1d3d3529 100644
--- a/tests/PhpSpreadsheetTests/DocumentGeneratorTest.php
+++ b/tests/PhpSpreadsheetTests/DocumentGeneratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Category as Cat;
diff --git a/tests/PhpSpreadsheetTests/Features/AutoFilter/Xlsx/BasicLoadTest.php b/tests/PhpSpreadsheetTests/Features/AutoFilter/Xlsx/BasicLoadTest.php
index 63c3c6fd2d..6131085b75 100644
--- a/tests/PhpSpreadsheetTests/Features/AutoFilter/Xlsx/BasicLoadTest.php
+++ b/tests/PhpSpreadsheetTests/Features/AutoFilter/Xlsx/BasicLoadTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Features\AutoFilter\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Functional/AbstractFunctional.php b/tests/PhpSpreadsheetTests/Functional/AbstractFunctional.php
index 60351d71b1..441e61e6d5 100644
--- a/tests/PhpSpreadsheetTests/Functional/AbstractFunctional.php
+++ b/tests/PhpSpreadsheetTests/Functional/AbstractFunctional.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
@@ -15,11 +17,9 @@ abstract class AbstractFunctional extends TestCase
     /**
      * Write spreadsheet to disk, reload and return it.
      *
-     * @param string $format
-     *
      * @return Spreadsheet
      */
-    protected function writeAndReload(Spreadsheet $spreadsheet, $format, ?callable $readerCustomizer = null, ?callable $writerCustomizer = null)
+    protected function writeAndReload(Spreadsheet $spreadsheet, string $format, ?callable $readerCustomizer = null, ?callable $writerCustomizer = null)
     {
         $filename = File::temporaryFilename();
         $writer = IOFactory::createWriter($spreadsheet, $format);
diff --git a/tests/PhpSpreadsheetTests/Functional/ActiveSheetTest.php b/tests/PhpSpreadsheetTests/Functional/ActiveSheetTest.php
index bc4b28944b..a6e1b33ffb 100644
--- a/tests/PhpSpreadsheetTests/Functional/ActiveSheetTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/ActiveSheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -18,10 +20,8 @@ public static function providerFormats(): array
      * Test load file with correct active sheet.
      *
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testActiveSheet($format): void
+    public function testActiveSheet(string $format): void
     {
         $spreadsheet = new Spreadsheet();
 
diff --git a/tests/PhpSpreadsheetTests/Functional/ColumnWidthTest.php b/tests/PhpSpreadsheetTests/Functional/ColumnWidthTest.php
index 18d4e4b6d2..fa6e958f25 100644
--- a/tests/PhpSpreadsheetTests/Functional/ColumnWidthTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/ColumnWidthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Functional/CommentsTest.php b/tests/PhpSpreadsheetTests/Functional/CommentsTest.php
index dcaf1d3618..36ec29b974 100644
--- a/tests/PhpSpreadsheetTests/Functional/CommentsTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/CommentsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Functional/ConditionalStopIfTrueTest.php b/tests/PhpSpreadsheetTests/Functional/ConditionalStopIfTrueTest.php
index c2e271cace..06f4afe0c3 100644
--- a/tests/PhpSpreadsheetTests/Functional/ConditionalStopIfTrueTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/ConditionalStopIfTrueTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -18,10 +20,8 @@ public static function providerFormats(): array
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testConditionalStopIfTrue($format): void
+    public function testConditionalStopIfTrue(string $format): void
     {
         $pCoordinate = 'A1:A3';
 
diff --git a/tests/PhpSpreadsheetTests/Functional/ConditionalTextTest.php b/tests/PhpSpreadsheetTests/Functional/ConditionalTextTest.php
index c8db3bf09a..de8c47e805 100644
--- a/tests/PhpSpreadsheetTests/Functional/ConditionalTextTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/ConditionalTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Functional/DrawingImageHyperlinkTest.php b/tests/PhpSpreadsheetTests/Functional/DrawingImageHyperlinkTest.php
index be350cedac..711f87e24a 100644
--- a/tests/PhpSpreadsheetTests/Functional/DrawingImageHyperlinkTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/DrawingImageHyperlinkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Cell\Hyperlink;
diff --git a/tests/PhpSpreadsheetTests/Functional/EnclosureTest.php b/tests/PhpSpreadsheetTests/Functional/EnclosureTest.php
index ebf79ee336..c1b7671922 100644
--- a/tests/PhpSpreadsheetTests/Functional/EnclosureTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/EnclosureTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -19,10 +21,8 @@ public static function providerFormats(): array
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testEnclosure($format): void
+    public function testEnclosure(string $format): void
     {
         $value = '<img alt="" src="http://example.com/image.jpg" />';
 
diff --git a/tests/PhpSpreadsheetTests/Functional/FreezePaneTest.php b/tests/PhpSpreadsheetTests/Functional/FreezePaneTest.php
index cee46bfa01..72e9ad1aa1 100644
--- a/tests/PhpSpreadsheetTests/Functional/FreezePaneTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/FreezePaneTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -18,10 +20,8 @@ public static function providerFormats(): array
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testFreezePane($format): void
+    public function testFreezePane(string $format): void
     {
         $cellSplit = 'B4';
         $topLeftCell = 'E7';
@@ -44,10 +44,8 @@ public function testFreezePane($format): void
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testFreezePaneWithInvalidSelectedCells($format): void
+    public function testFreezePaneWithInvalidSelectedCells(string $format): void
     {
         $cellSplit = 'A7';
         $topLeftCell = 'A24';
@@ -74,10 +72,8 @@ public function testFreezePaneWithInvalidSelectedCells($format): void
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testFreezePaneUserSelectedCell($format): void
+    public function testFreezePaneUserSelectedCell(string $format): void
     {
         $spreadsheet = new Spreadsheet();
         $worksheet = $spreadsheet->getActiveSheet();
@@ -105,10 +101,8 @@ public function testFreezePaneUserSelectedCell($format): void
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testNoFreezePaneUserSelectedCell($format): void
+    public function testNoFreezePaneUserSelectedCell(string $format): void
     {
         $spreadsheet = new Spreadsheet();
         $worksheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Functional/MergedCellsTest.php b/tests/PhpSpreadsheetTests/Functional/MergedCellsTest.php
index b5ef4df40e..c99826bfd6 100644
--- a/tests/PhpSpreadsheetTests/Functional/MergedCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/MergedCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -18,10 +20,8 @@ public static function providerFormats(): array
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testMergedCells($format): void
+    public function testMergedCells(string $format): void
     {
         $spreadsheet = new Spreadsheet();
         $spreadsheet->setActiveSheetIndex(0);
diff --git a/tests/PhpSpreadsheetTests/Functional/PrintAreaTest.php b/tests/PhpSpreadsheetTests/Functional/PrintAreaTest.php
index 1ceed4572b..535f927feb 100644
--- a/tests/PhpSpreadsheetTests/Functional/PrintAreaTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/PrintAreaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Reader\BaseReader;
@@ -17,10 +19,8 @@ public static function providerFormats(): array
 
     /**
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testPageSetup($format): void
+    public function testPageSetup(string $format): void
     {
         // Create new workbook with 6 sheets and different print areas
         $spreadsheet = new Spreadsheet();
diff --git a/tests/PhpSpreadsheetTests/Functional/ReadBlankCellsTest.php b/tests/PhpSpreadsheetTests/Functional/ReadBlankCellsTest.php
index 6984a9aaee..ad1729b003 100644
--- a/tests/PhpSpreadsheetTests/Functional/ReadBlankCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/ReadBlankCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -21,10 +23,8 @@ public static function providerSheetFormat(): array
      * Test generate file with some empty cells.
      *
      * @dataProvider providerSheetFormat
-     *
-     * @param mixed $format
      */
-    public function testXlsxLoadWithNoBlankCells($format): void
+    public function testXlsxLoadWithNoBlankCells(mixed $format): void
     {
         $spreadsheet = new Spreadsheet();
         $spreadsheet->getActiveSheet()->getCell('B2')->setValue('');
diff --git a/tests/PhpSpreadsheetTests/Functional/ReadFilterFilter.php b/tests/PhpSpreadsheetTests/Functional/ReadFilterFilter.php
index a9a26a5ee8..755ee2d340 100644
--- a/tests/PhpSpreadsheetTests/Functional/ReadFilterFilter.php
+++ b/tests/PhpSpreadsheetTests/Functional/ReadFilterFilter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -11,11 +13,9 @@ class ReadFilterFilter implements IReadFilter
      * @param int $row Row number
      * @param string $worksheetName Optional worksheet name
      *
-     * @return bool
-     *
      * @see \PhpOffice\PhpSpreadsheet\Reader\IReadFilter::readCell()
      */
-    public function readCell($column, $row, $worksheetName = '')
+    public function readCell($column, $row, $worksheetName = ''): bool
     {
         // define filter range
         $rowMin = 2;
diff --git a/tests/PhpSpreadsheetTests/Functional/ReadFilterTest.php b/tests/PhpSpreadsheetTests/Functional/ReadFilterTest.php
index 9560913ee4..75c8206d0b 100644
--- a/tests/PhpSpreadsheetTests/Functional/ReadFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/ReadFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -32,10 +34,8 @@ public static function providerCellsValues(): array
      * Test load Xlsx file with many empty cells with no filter used.
      *
      * @dataProvider providerCellsValues
-     *
-     * @param mixed $format
      */
-    public function testXlsxLoadWithoutReadFilter($format, array $arrayData): void
+    public function testXlsxLoadWithoutReadFilter(mixed $format, array $arrayData): void
     {
         $spreadsheet = new Spreadsheet();
 
@@ -59,10 +59,8 @@ public function testXlsxLoadWithoutReadFilter($format, array $arrayData): void
      * Test load Xlsx file with many empty cells (and big max row number) with readfilter.
      *
      * @dataProvider providerCellsValues
-     *
-     * @param mixed $format
      */
-    public function testXlsxLoadWithReadFilter($format, array $arrayData): void
+    public function testXlsxLoadWithReadFilter(mixed $format, array $arrayData): void
     {
         $spreadsheet = new Spreadsheet();
         $spreadsheet->getActiveSheet()->fromArray($arrayData, null, 'A1');
diff --git a/tests/PhpSpreadsheetTests/Functional/SelectedCellsTest.php b/tests/PhpSpreadsheetTests/Functional/SelectedCellsTest.php
index 4444a29314..89a7327e58 100644
--- a/tests/PhpSpreadsheetTests/Functional/SelectedCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/SelectedCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -17,10 +19,8 @@ public static function providerFormats(): array
      * Test load file with correct selected cells.
      *
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testSelectedCells($format): void
+    public function testSelectedCells(string $format): void
     {
         $spreadsheet = new Spreadsheet();
 
diff --git a/tests/PhpSpreadsheetTests/Functional/StreamTest.php b/tests/PhpSpreadsheetTests/Functional/StreamTest.php
index e0a4b27d65..3430b7a31b 100644
--- a/tests/PhpSpreadsheetTests/Functional/StreamTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/StreamTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php b/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php
index 14343d32b7..e90cf42677 100644
--- a/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/TypeAttributePreservationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods as ReaderOds;
@@ -31,10 +33,8 @@ public static function providerFormulae(): array
      * Ensure saved spreadsheets maintain the correct data type.
      *
      * @dataProvider providerFormulae
-     *
-     * @param string $format
      */
-    public function testFormulae($format, array $values): void
+    public function testFormulae(string $format, array $values): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
@@ -65,10 +65,8 @@ public static function customizeWriter(WriterXlsx $writer): void
      * Ensure saved spreadsheets maintain the correct data type.
      *
      * @dataProvider providerFormulae
-     *
-     * @param string $format
      */
-    public function testFormulaeNoPrecalc($format, array $values): void
+    public function testFormulaeNoPrecalc(string $format, array $values): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Functional/WorkbookViewAttributesTest.php b/tests/PhpSpreadsheetTests/Functional/WorkbookViewAttributesTest.php
index 9998dceddc..5c21443a95 100644
--- a/tests/PhpSpreadsheetTests/Functional/WorkbookViewAttributesTest.php
+++ b/tests/PhpSpreadsheetTests/Functional/WorkbookViewAttributesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Functional;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -21,10 +23,8 @@ public static function providerFormats(): array
      * @see https://github.com/PHPOffice/PhpSpreadsheet/issues/523
      *
      * @dataProvider providerFormats
-     *
-     * @param string $format
      */
-    public function testPreserveWorkbookViewAttributes($format): void
+    public function testPreserveWorkbookViewAttributes(string $format): void
     {
         // Create a dummy workbook with two worksheets
         $workbook = new Spreadsheet();
diff --git a/tests/PhpSpreadsheetTests/HashTableTest.php b/tests/PhpSpreadsheetTests/HashTableTest.php
index 09c2fc9283..086ee6f056 100644
--- a/tests/PhpSpreadsheetTests/HashTableTest.php
+++ b/tests/PhpSpreadsheetTests/HashTableTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Comment; // need Comparable object
@@ -18,10 +20,7 @@ public static function createArray(): array
         return [$comment1, $comment2];
     }
 
-    /**
-     * @param mixed $comment
-     */
-    public static function getAuthor($comment): string
+    public static function getAuthor(mixed $comment): string
     {
         return ($comment instanceof Comment) ? $comment->getAuthor() : '';
     }
diff --git a/tests/PhpSpreadsheetTests/Helper/DimensionTest.php b/tests/PhpSpreadsheetTests/Helper/DimensionTest.php
index 5fdc3b75e6..e6a823c763 100644
--- a/tests/PhpSpreadsheetTests/Helper/DimensionTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/DimensionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Helper;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Helper/HandlerTest.php b/tests/PhpSpreadsheetTests/Helper/HandlerTest.php
index 8eee3064f3..bb8bf751f4 100644
--- a/tests/PhpSpreadsheetTests/Helper/HandlerTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/HandlerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Helper;
 
 use PhpOffice\PhpSpreadsheet\Helper\Handler;
diff --git a/tests/PhpSpreadsheetTests/Helper/HtmlTest.php b/tests/PhpSpreadsheetTests/Helper/HtmlTest.php
index 6bcb973010..8fb6c3b3d7 100644
--- a/tests/PhpSpreadsheetTests/Helper/HtmlTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/HtmlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Helper;
 
 use PhpOffice\PhpSpreadsheet\Helper\Html;
@@ -9,11 +11,8 @@ class HtmlTest extends TestCase
 {
     /**
      * @dataProvider providerUtf8EncodingSupport
-     *
-     * @param mixed $expected
-     * @param mixed $input
      */
-    public function testUtf8EncodingSupport($expected, $input): void
+    public function testUtf8EncodingSupport(mixed $expected, mixed $input): void
     {
         $html = new Html();
         $actual = $html->toRichTextObject($input);
diff --git a/tests/PhpSpreadsheetTests/Helper/SampleCoverageTest.php b/tests/PhpSpreadsheetTests/Helper/SampleCoverageTest.php
index f3f616fe63..2c54dd68fc 100644
--- a/tests/PhpSpreadsheetTests/Helper/SampleCoverageTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/SampleCoverageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Helper;
 
 use PhpOffice\PhpSpreadsheet\Helper\Sample;
diff --git a/tests/PhpSpreadsheetTests/Helper/SampleTest.php b/tests/PhpSpreadsheetTests/Helper/SampleTest.php
index 387597f7d1..7ec3b37bfb 100644
--- a/tests/PhpSpreadsheetTests/Helper/SampleTest.php
+++ b/tests/PhpSpreadsheetTests/Helper/SampleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Helper;
 
 use PhpOffice\PhpSpreadsheet\Helper\Sample;
diff --git a/tests/PhpSpreadsheetTests/IOFactoryTest.php b/tests/PhpSpreadsheetTests/IOFactoryTest.php
index 4f46a6b268..bf894c5668 100644
--- a/tests/PhpSpreadsheetTests/IOFactoryTest.php
+++ b/tests/PhpSpreadsheetTests/IOFactoryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
@@ -13,11 +15,8 @@ class IOFactoryTest extends TestCase
 {
     /**
      * @dataProvider providerCreateWriter
-     *
-     * @param string $name
-     * @param string $expected
      */
-    public function testCreateWriter($name, $expected): void
+    public function testCreateWriter(string $name, string $expected): void
     {
         $spreadsheet = new Spreadsheet();
         $actual = IOFactory::createWriter($spreadsheet, $name);
@@ -48,11 +47,8 @@ public function testRegisterWriter(): void
 
     /**
      * @dataProvider providerCreateReader
-     *
-     * @param string $name
-     * @param string $expected
      */
-    public function testCreateReader($name, $expected): void
+    public function testCreateReader(string $name, string $expected): void
     {
         $actual = IOFactory::createReader($name);
         self::assertSame($expected, get_class($actual));
diff --git a/tests/PhpSpreadsheetTests/NamedFormulaTest.php b/tests/PhpSpreadsheetTests/NamedFormulaTest.php
index 28857abe6a..103a1250b2 100644
--- a/tests/PhpSpreadsheetTests/NamedFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/NamedFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\NamedFormula;
@@ -9,8 +11,7 @@
 
 class NamedFormulaTest extends TestCase
 {
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private \PhpOffice\PhpSpreadsheet\Spreadsheet $spreadsheet;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/NamedRange2Test.php b/tests/PhpSpreadsheetTests/NamedRange2Test.php
index 9303c9afb3..6c20e145dd 100644
--- a/tests/PhpSpreadsheetTests/NamedRange2Test.php
+++ b/tests/PhpSpreadsheetTests/NamedRange2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\DefinedName;
diff --git a/tests/PhpSpreadsheetTests/NamedRangeTest.php b/tests/PhpSpreadsheetTests/NamedRangeTest.php
index 9440ef21ef..0d69ccb80f 100644
--- a/tests/PhpSpreadsheetTests/NamedRangeTest.php
+++ b/tests/PhpSpreadsheetTests/NamedRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
@@ -9,8 +11,7 @@
 
 class NamedRangeTest extends TestCase
 {
-    /** @var Spreadsheet */
-    private $spreadsheet;
+    private \PhpOffice\PhpSpreadsheet\Spreadsheet $spreadsheet;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Reader/BaseNoLoad.php b/tests/PhpSpreadsheetTests/Reader/BaseNoLoad.php
index 177d8a9392..1673f2c95b 100644
--- a/tests/PhpSpreadsheetTests/Reader/BaseNoLoad.php
+++ b/tests/PhpSpreadsheetTests/Reader/BaseNoLoad.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader;
 
 use PhpOffice\PhpSpreadsheet\Reader\BaseReader;
diff --git a/tests/PhpSpreadsheetTests/Reader/BaseNoLoadTest.php b/tests/PhpSpreadsheetTests/Reader/BaseNoLoadTest.php
index 558189673b..6943e8cd18 100644
--- a/tests/PhpSpreadsheetTests/Reader/BaseNoLoadTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/BaseNoLoadTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvCallbackTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvCallbackTest.php
index 51f4c760b1..753ddfec3e 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvCallbackTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvCallbackTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
@@ -13,10 +15,7 @@ protected function tearDown(): void
         Csv::setConstructorCallback(null);
     }
 
-    /**
-     * @param mixed $obj
-     */
-    public function callbackDoNothing($obj): void
+    public function callbackDoNothing(mixed $obj): void
     {
         self::assertInstanceOf(Csv::class, $obj);
     }
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousFilter.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousFilter.php
index 31e60bdd40..7ee93665e4 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousFilter.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousFilter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -52,7 +54,7 @@ public function filter0(int $row): bool
         return false;
     }
 
-    public function readCell($columnAddress, $row, $worksheetName = '')
+    public function readCell($columnAddress, $row, $worksheetName = ''): bool
     {
         if ($this->filterType == 1) {
             return $this->filter1($row);
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousTest.php
index 8c28c1e705..abb85d73e8 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvContiguousTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv;
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvEncodingTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvEncodingTest.php
index a216eee5fd..7ce3c5f4ff 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvEncodingTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvEncodingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv;
@@ -9,11 +11,8 @@ class CsvEncodingTest extends TestCase
 {
     /**
      * @dataProvider providerEncodings
-     *
-     * @param string $filename
-     * @param string $encoding
      */
-    public function testEncodings($filename, $encoding): void
+    public function testEncodings(string $filename, string $encoding): void
     {
         $reader = new Csv();
         $reader->setInputEncoding($encoding);
@@ -24,11 +23,8 @@ public function testEncodings($filename, $encoding): void
 
     /**
      * @dataProvider providerEncodings
-     *
-     * @param string $filename
-     * @param string $encoding
      */
-    public function testWorkSheetInfo($filename, $encoding): void
+    public function testWorkSheetInfo(string $filename, string $encoding): void
     {
         $reader = new Csv();
         $reader->setInputEncoding($encoding);
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2232Test.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2232Test.php
index 82256365f5..ae305d42f0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2232Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2232Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
@@ -11,13 +13,9 @@
 
 class CsvIssue2232Test extends TestCase
 {
-    /**
-     * @var IValueBinder
-     */
-    private $valueBinder;
+    private IValueBinder $valueBinder;
 
-    /** @var string */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
@@ -33,11 +31,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerIssue2232
-     *
-     * @param mixed $b2Value
-     * @param mixed $b3Value
      */
-    public function testBooleanConversions(bool $useStringBinder, ?bool $preserveBoolString, $b2Value, $b3Value): void
+    public function testBooleanConversions(bool $useStringBinder, ?bool $preserveBoolString, bool|string $b2Value, bool|string $b3Value): void
     {
         if ($useStringBinder) {
             $binder = new StringValueBinder();
@@ -69,11 +64,8 @@ public static function providerIssue2232(): array
 
     /**
      * @dataProvider providerIssue2232locale
-     *
-     * @param mixed $b4Value
-     * @param mixed $b5Value
      */
-    public function testBooleanConversionsLocaleAware(bool $useStringBinder, ?bool $preserveBoolString, $b4Value, $b5Value): void
+    public function testBooleanConversionsLocaleAware(bool $useStringBinder, ?bool $preserveBoolString, mixed $b4Value, mixed $b5Value): void
     {
         if ($useStringBinder) {
             $binder = new StringValueBinder();
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2840Test.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2840Test.php
index 760006835c..48e9027a9a 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2840Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvIssue2840Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv;
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvLineEndingTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvLineEndingTest.php
index 1ac17b981d..64dd48cb58 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvLineEndingTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvLineEndingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv;
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvLoadFromStringTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvLoadFromStringTest.php
index f0ebf8d327..a485db93b9 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvLoadFromStringTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvLoadFromStringTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv;
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatLocaleTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatLocaleTest.php
index 5e9af62dc6..9550636b3c 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatLocaleTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatLocaleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
@@ -8,10 +10,7 @@
 
 class CsvNumberFormatLocaleTest extends TestCase
 {
-    /**
-     * @var bool
-     */
-    private $localeAdjusted;
+    private bool $localeAdjusted;
 
     /**
      * @var false|string
@@ -53,10 +52,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerNumberFormatNoConversionTest
-     *
-     * @param mixed $expectedValue
      */
-    public function testNumberFormatNoConversion($expectedValue, string $expectedFormat, string $cellAddress): void
+    public function testNumberFormatNoConversion(mixed $expectedValue, string $expectedFormat, string $cellAddress): void
     {
         if (!$this->localeAdjusted) {
             self::markTestSkipped('Unable to set locale for testing.');
@@ -95,11 +92,9 @@ public static function providerNumberFormatNoConversionTest(): array
     /**
      * @dataProvider providerNumberValueConversionTest
      *
-     * @param mixed $expectedValue
-     *
      * @runInSeparateProcess
      */
-    public function testNumberValueConversion($expectedValue, string $cellAddress): void
+    public function testNumberValueConversion(mixed $expectedValue, string $cellAddress): void
     {
         if (!$this->localeAdjusted) {
             self::markTestSkipped('Unable to set locale for testing.');
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatTest.php
index 0022fd15ad..3cf4047092 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvNumberFormatTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
@@ -26,10 +28,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider providerNumberFormatNoConversionTest
-     *
-     * @param mixed $expectedValue
      */
-    public function testNumberFormatNoConversion($expectedValue, string $expectedFormat, string $cellAddress): void
+    public function testNumberFormatNoConversion(int|string $expectedValue, string $expectedFormat, string $cellAddress): void
     {
         $spreadsheet = $this->csvReader->load($this->filename);
         $worksheet = $spreadsheet->getActiveSheet();
@@ -63,10 +63,8 @@ public static function providerNumberFormatNoConversionTest(): array
 
     /**
      * @dataProvider providerNumberValueConversionTest
-     *
-     * @param mixed $expectedValue
      */
-    public function testNumberValueConversion($expectedValue, string $cellAddress): void
+    public function testNumberValueConversion(mixed $expectedValue, string $cellAddress): void
     {
         $this->csvReader->castFormattedNumberToNumeric(true);
         $spreadsheet = $this->csvReader->load($this->filename);
@@ -114,10 +112,8 @@ public static function providerNumberValueConversionTest(): array
 
     /**
      * @dataProvider providerNumberFormatConversionTest
-     *
-     * @param mixed $expectedValue
      */
-    public function testNumberFormatConversion($expectedValue, string $expectedFormat, string $cellAddress): void
+    public function testNumberFormatConversion(mixed $expectedValue, string $expectedFormat, string $cellAddress): void
     {
         $this->csvReader->castFormattedNumberToNumeric(true, true);
         $spreadsheet = $this->csvReader->load($this->filename);
diff --git a/tests/PhpSpreadsheetTests/Reader/Csv/CsvTest.php b/tests/PhpSpreadsheetTests/Reader/Csv/CsvTest.php
index 8a0308a4e0..3f4375df85 100644
--- a/tests/PhpSpreadsheetTests/Reader/Csv/CsvTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Csv/CsvTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv;
@@ -10,13 +12,8 @@ class CsvTest extends TestCase
 {
     /**
      * @dataProvider providerDelimiterDetection
-     *
-     * @param string $filename
-     * @param string $expectedDelimiter
-     * @param string $cell
-     * @param float|int|string $expectedValue
      */
-    public function testDelimiterDetection($filename, $expectedDelimiter, $cell, $expectedValue): void
+    public function testDelimiterDetection(string $filename, string $expectedDelimiter, string $cell, string|float|int|null $expectedValue): void
     {
         $reader = new Csv();
         $delim1 = $reader->getDelimiter();
@@ -92,11 +89,8 @@ public static function providerDelimiterDetection(): array
 
     /**
      * @dataProvider providerCanLoad
-     *
-     * @param bool $expected
-     * @param string $filename
      */
-    public function testCanLoad($expected, $filename): void
+    public function testCanLoad(bool $expected, string $filename): void
     {
         $reader = new Csv();
         self::assertSame($expected, $reader->canRead($filename));
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/AutoFilterTest.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/AutoFilterTest.php
index fd309fbd92..be82e77f30 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/AutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/AutoFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use PhpOffice\PhpSpreadsheet\Reader\Gnumeric;
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericFilter.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericFilter.php
index 8d8fd62b40..b33bb086f3 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericFilter.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericFilter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -7,7 +9,7 @@
 /**  Define a Read Filter class implementing IReadFilter  */
 class GnumericFilter implements IReadFilter
 {
-    public function readCell($columnAddress, $row, $worksheetName = '')
+    public function readCell($columnAddress, $row, $worksheetName = ''): bool
     {
         return $row !== 4;
     }
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericInfoTest.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericInfoTest.php
index 7bc0077639..74b9a8bded 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericInfoTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericInfoTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericLoadTest.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericLoadTest.php
index 7e89e3acfc..1d8d0060dd 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericLoadTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericLoadTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use DateTimeZone;
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericStylesTest.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericStylesTest.php
index 931fbc40c9..e8d332895d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericStylesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/GnumericStylesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/HiddenWorksheetTest.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/HiddenWorksheetTest.php
index 6110702188..021ece1cbe 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/HiddenWorksheetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/HiddenWorksheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use PhpOffice\PhpSpreadsheet\Reader\Gnumeric;
diff --git a/tests/PhpSpreadsheetTests/Reader/Gnumeric/PageSetupTest.php b/tests/PhpSpreadsheetTests/Reader/Gnumeric/PageSetupTest.php
index bac8f42506..16a4708109 100644
--- a/tests/PhpSpreadsheetTests/Reader/Gnumeric/PageSetupTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Gnumeric/PageSetupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Gnumeric;
 
 use PhpOffice\PhpSpreadsheet\Reader\Gnumeric;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlBorderTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlBorderTest.php
index c60fea5b7a..a525b321a5 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlBorderTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlBorderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlHelper.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlHelper.php
index a6be40c921..78986c8ca2 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlHelper.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlHelper.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlImageTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlImageTest.php
index fe0117cacf..b56a316a14 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlImageTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlImageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Drawing;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlLibxmlTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlLibxmlTest.php
index d5f5044aa0..bb29eb6c55 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlLibxmlTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlLibxmlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
@@ -17,8 +19,7 @@
  */
 class HtmlLibxmlTest extends TestCase
 {
-    /** @var bool */
-    private $useErrors;
+    private bool $useErrors;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlLoadStringTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlLoadStringTest.php
index 5fa7ccf43f..b567173d4b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlLoadStringTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlLoadStringTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlPhpunit10Test.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlPhpunit10Test.php
index fce30b121a..175f0e8bb5 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlPhpunit10Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlPhpunit10Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
@@ -14,8 +16,7 @@
  */
 class HtmlPhpunit10Test extends TestCase
 {
-    /** @var string */
-    private static $errorString;
+    private static string $errorString;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlTagsTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlTagsTest.php
index 45a098a348..b4e2484361 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlTagsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlTagsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php
index 5f80b2581b..afb01cbfef 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
@@ -64,11 +66,8 @@ public static function providerCanReadVerySmallFile(): array
 
     /**
      * @dataProvider providerCanReadVerySmallFile
-     *
-     * @param bool $expected
-     * @param string $content
      */
-    public function testCanReadVerySmallFile($expected, $content): void
+    public function testCanReadVerySmallFile(bool $expected, string $content): void
     {
         $filename = HtmlHelper::createHtml($content);
         $reader = new Html();
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/Issue2029Test.php b/tests/PhpSpreadsheetTests/Reader/Html/Issue2029Test.php
index d307935043..76b6477839 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/Issue2029Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/Issue2029Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
@@ -57,43 +59,43 @@ public function testIssue2029(): void
                   </th>
                   <th class="text-center">
                       Apellido y Nombre
-                  </th>                        
+                  </th>
                   <th class="text-center">
                       Obra Social
                   </th>
                   <th class="text-center">
                     Corresponde Reducci&oacute;n?
-                  </th>                        
+                  </th>
                 </tr>
-                
+
                 <tr>
                     <td class="text-center">
                       12345678901
                     </td>
                     <td class="text-center">
                       EMILIANO ZAPATA SALAZAR
-                    </td>                        
+                    </td>
                     <td class="text-center">
                       101208
                     </td>
                     <td class="text-center">
                       Yes
-                    </td>                        
+                    </td>
                 </tr>
-                
+
                 <tr>
                     <td class="text-center">
                       23456789012
                     </td>
                     <td class="text-center">
                       FRANCISCO PANCHO VILLA
-                    </td>                        
+                    </td>
                     <td class="text-center">
                       101208
                     </td>
                     <td class="text-center">
                       No
-                    </td>                        
+                    </td>
                 </tr>
               </table>
             </body>
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/Issue2810Test.php b/tests/PhpSpreadsheetTests/Reader/Html/Issue2810Test.php
index 5e6e738695..b2ade3d5fc 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/Issue2810Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/Issue2810Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/Issue2942Test.php b/tests/PhpSpreadsheetTests/Reader/Html/Issue2942Test.php
index 8e25bd6f75..5fbb6248b0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/Issue2942Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/Issue2942Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Html;
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/ViewportTest.php b/tests/PhpSpreadsheetTests/Reader/Html/ViewportTest.php
index 1a167455a2..fb9e3e9c90 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/ViewportTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/ViewportTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Html;
 
 use PhpOffice\PhpSpreadsheet\Document\Properties;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/AutoFilterTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/AutoFilterTest.php
index 1fd709cacd..2f1d1a4119 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/AutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/AutoFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/DefinedNamesTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/DefinedNamesTest.php
index e93be49451..d5a572f77c 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/DefinedNamesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/DefinedNamesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/EmptyFileTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/EmptyFileTest.php
index 5876eaab1c..9e7c15515d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/EmptyFileTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/EmptyFileTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/HiddenMergeCellsTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/HiddenMergeCellsTest.php
index 3f38631c47..6612355b70 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/HiddenMergeCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/HiddenMergeCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/HiddenWorksheetTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/HiddenWorksheetTest.php
index 70b5d4b90f..9793a3c094 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/HiddenWorksheetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/HiddenWorksheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/HyperlinkTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/HyperlinkTest.php
index 2dc5f9cfaf..c4bbef0ec6 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/HyperlinkTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/HyperlinkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/InvalidFileTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/InvalidFileTest.php
index d56af4ded3..550763756f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/InvalidFileTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/InvalidFileTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/Issue2810Test.php b/tests/PhpSpreadsheetTests/Reader/Ods/Issue2810Test.php
index bbb697b8ac..7677e43a92 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/Issue2810Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/Issue2810Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/MergeRangeTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/MergeRangeTest.php
index 5c36c65b85..a175c6f03d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/MergeRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/MergeRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/OdsInfoTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/OdsInfoTest.php
index 1de4252f8b..e780d32b6b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/OdsInfoTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/OdsInfoTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/OdsPropertiesTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/OdsPropertiesTest.php
index 3ba99e52ba..b9722ec13b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/OdsPropertiesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/OdsPropertiesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Document\Properties;
@@ -9,10 +11,7 @@
 
 class OdsPropertiesTest extends AbstractFunctional
 {
-    /**
-     * @var string
-     */
-    private $timeZone;
+    private string $timeZone;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php
index 115b0c0198..fd17ae037d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/OdsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
@@ -22,10 +24,7 @@ class OdsTest extends TestCase
     /** @var string */
     private $incompleteMessage = 'Features not implemented yet';
 
-    /**
-     * @var string
-     */
-    private $timeZone;
+    private string $timeZone;
 
     protected function setUp(): void
     {
@@ -38,20 +37,14 @@ protected function tearDown(): void
         date_default_timezone_set($this->timeZone);
     }
 
-    /**
-     * @return Spreadsheet
-     */
-    private function loadOdsTestFile()
+    private function loadOdsTestFile(): Spreadsheet
     {
         $reader = new Ods();
 
         return $reader->loadIntoExisting(self::ODS_TEST_FILE, new Spreadsheet());
     }
 
-    /**
-     * @return Spreadsheet
-     */
-    protected function loadDataFile()
+    protected function loadDataFile(): Spreadsheet
     {
         $reader = new Ods();
 
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupBug1772Test.php b/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupBug1772Test.php
index 7fc7e53763..568bb602c0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupBug1772Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupBug1772Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupTest.php
index 0ee190da54..227a11c6ef 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/PageSetupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\Ods;
diff --git a/tests/PhpSpreadsheetTests/Reader/Ods/RepeatedColumnsTest.php b/tests/PhpSpreadsheetTests/Reader/Ods/RepeatedColumnsTest.php
index 14309afa68..7b6e9dbb5b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Ods/RepeatedColumnsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Ods/RepeatedColumnsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Ods;
 
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
diff --git a/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php b/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php
index 34bf33ab63..8215b87818 100644
--- a/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Security/XmlScannerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Security;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
@@ -13,11 +15,8 @@ class XmlScannerTest extends TestCase
 {
     /**
      * @dataProvider providerValidXML
-     *
-     * @param mixed $filename
-     * @param mixed $expectedResult
      */
-    public function testValidXML($filename, $expectedResult): void
+    public function testValidXML(mixed $filename, mixed $expectedResult): void
     {
         $reader = XmlScanner::getInstance(new \PhpOffice\PhpSpreadsheet\Reader\Xml());
         $result = $reader->scanFile($filename);
@@ -40,10 +39,8 @@ public static function providerValidXML(): array
 
     /**
      * @dataProvider providerInvalidXML
-     *
-     * @param mixed $filename
      */
-    public function testInvalidXML($filename): void
+    public function testInvalidXML(mixed $filename): void
     {
         $this->expectException(\PhpOffice\PhpSpreadsheet\Reader\Exception::class);
 
@@ -95,11 +92,8 @@ public function testGetSecurityScannerForNonXmlBasedReader2(): void
 
     /**
      * @dataProvider providerValidXMLForCallback
-     *
-     * @param mixed $filename
-     * @param mixed $expectedResult
      */
-    public function testSecurityScanWithCallback($filename, $expectedResult): void
+    public function testSecurityScanWithCallback(mixed $filename, mixed $expectedResult): void
     {
         $fileReader = new Xlsx();
         $scanner = $fileReader->getSecurityScannerOrThrow();
diff --git a/tests/PhpSpreadsheetTests/Reader/Slk/SlkCommentsTest.php b/tests/PhpSpreadsheetTests/Reader/Slk/SlkCommentsTest.php
index 6f8a7ef51a..f77bc86d28 100644
--- a/tests/PhpSpreadsheetTests/Reader/Slk/SlkCommentsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Slk/SlkCommentsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Slk;
 
 use PhpOffice\PhpSpreadsheet\Reader\Slk;
diff --git a/tests/PhpSpreadsheetTests/Reader/Slk/SlkTest.php b/tests/PhpSpreadsheetTests/Reader/Slk/SlkTest.php
index 2d51955c95..ac8b381df4 100644
--- a/tests/PhpSpreadsheetTests/Reader/Slk/SlkTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Slk/SlkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Slk;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Utility/File.php b/tests/PhpSpreadsheetTests/Reader/Utility/File.php
index f2283326e1..0290617b51 100644
--- a/tests/PhpSpreadsheetTests/Reader/Utility/File.php
+++ b/tests/PhpSpreadsheetTests/Reader/Utility/File.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Utility;
 
 class File
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php
index bd1cfa4c79..ee571b9568 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls\Color\BIFF5;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ColourTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ColourTest.php
index d17e7e167d..45dab07262 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/ColourTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ColourTest.php
@@ -1,17 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
-use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
 
 class ColourTest extends AbstractFunctional
 {
-    /**
-     * @var Spreadsheet
-     */
-    private $spreadsheet;
+    private \PhpOffice\PhpSpreadsheet\Spreadsheet $spreadsheet;
 
     protected function setup(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingBasicTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingBasicTest.php
index e399c6d81a..684c3d2630 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingBasicTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingBasicTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingExpressionTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingExpressionTest.php
index 0f683be26e..abdfb90884 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingExpressionTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ConditionalFormattingExpressionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/DataValidationTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/DataValidationTest.php
index 0c9f51ce7a..80619af997 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/DataValidationTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/DataValidationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/DefinedNameTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/DefinedNameTest.php
index c956158087..05290bd849 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/DefinedNameTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/DefinedNameTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php
index 0b8839bf06..e9c82ffa76 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls\ErrorCode;
@@ -8,11 +10,9 @@
 class ErrorCodeMapTest extends TestCase
 {
     /**
-     * @param bool|string $expected
-     *
      * @dataProvider errorCodeMapProvider
      */
-    public function testErrorCode($expected, int $index): void
+    public function testErrorCode(bool|string $expected, int $index): void
     {
         self::assertSame($expected, ErrorCode::lookup($index));
     }
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/FormulasTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/FormulasTest.php
index 1617f89d7d..86e551ba32 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/FormulasTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/FormulasTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/HiddenMergeCellsTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/HiddenMergeCellsTest.php
index 0a59b7d447..7300c7ec96 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/HiddenMergeCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/HiddenMergeCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/HiddenWorksheetTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/HiddenWorksheetTest.php
index aa50599c3d..9048439236 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/HiddenWorksheetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/HiddenWorksheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/InfoNamesTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/InfoNamesTest.php
index a493d65be4..4f9073a7b4 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/InfoNamesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/InfoNamesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/Issue2463Test.php b/tests/PhpSpreadsheetTests/Reader/Xls/Issue2463Test.php
index 902424fc75..9de1c4ba9f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/Issue2463Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/Issue2463Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/Md5Test.php b/tests/PhpSpreadsheetTests/Reader/Xls/Md5Test.php
index f86d1c5535..550f127670 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/Md5Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/Md5Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls\MD5;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/NonExistentFileTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/NonExistentFileTest.php
index 76db7b62a4..f923a01f5b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/NonExistentFileTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/NonExistentFileTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/NumberFormatGeneralTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/NumberFormatGeneralTest.php
index 3bfea8bf22..15711cad8f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/NumberFormatGeneralTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/NumberFormatGeneralTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/PageBreakTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/PageBreakTest.php
index 6a2bd40917..475b4d83ed 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/PageBreakTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/PageBreakTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/PageSetupTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/PageSetupTest.php
index f90595465e..2eb2bc633a 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/PageSetupTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/PageSetupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/Rc4Test.php b/tests/PhpSpreadsheetTests/Reader/Xls/Rc4Test.php
index c3056c08bf..453ff2b5e0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/Rc4Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/Rc4Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls\RC4;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/RichTextSizeTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/RichTextSizeTest.php
index cf45dec1a3..39f2edd790 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/RichTextSizeTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/RichTextSizeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/SheetProtectionTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/SheetProtectionTest.php
index e6f827719a..c6d040eb81 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/SheetProtectionTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/SheetProtectionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/XlsTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/XlsTest.php
index 03c3afd4c5..4cdfc06f68 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xls/XlsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/XlsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/AbsolutePathTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/AbsolutePathTest.php
index 6a886abb4a..a99eab8030 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/AbsolutePathTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/AbsolutePathTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilter2Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilter2Test.php
index 7a26439481..be67423f80 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilter2Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilter2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterEvaluateTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterEvaluateTest.php
index cb54c567e5..70f332a168 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterEvaluateTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterEvaluateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterTest.php
index 50c1b3c120..276a3e4fb2 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/AutoFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx\AutoFilter;
@@ -30,12 +32,8 @@ public static function loadDataProvider(): array
 
     /**
      * @dataProvider loadDataProvider
-     *
-     * @param string $ref
-     * @param int $expectedReadAutoFilterCalled
-     * @param string $expectedRef
      */
-    public function testLoad($ref, $expectedReadAutoFilterCalled, $expectedRef): void
+    public function testLoad(string $ref, int $expectedReadAutoFilterCalled, string $expectedRef): void
     {
         $worksheetAutoFilter = $this->getMockBuilder(WorksheetAutoFilter::class)
             ->disableOriginalConstructor()
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ChartSheetTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ChartSheetTest.php
index e7862697ee..e433f01aa9 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ChartSheetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ChartSheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ColorTabTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ColorTabTest.php
index 2218ace14f..d16adeb99a 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ColorTabTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ColorTabTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/CommentTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/CommentTest.php
index cb7635e9e2..1eb9eca01a 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/CommentTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/CommentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/CondNumFmtTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/CondNumFmtTest.php
index 350baa76b8..6797c7afae 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/CondNumFmtTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/CondNumFmtTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalBorderTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalBorderTest.php
index df5ebe64ab..1d65d720cd 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalBorderTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalBorderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalFormattingDataBarXlsxTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalFormattingDataBarXlsxTest.php
index 0ec25d8e7c..6a0ac7def0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalFormattingDataBarXlsxTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalFormattingDataBarXlsxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalNoFormatSetTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalNoFormatSetTest.php
index 570a613ea5..86729c1c00 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalNoFormatSetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalNoFormatSetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalTest.php
index 29f0c55435..15af02dffb 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ConditionalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/CoverageGapsTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/CoverageGapsTest.php
index 6630a3fe61..8d6e6137e4 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/CoverageGapsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/CoverageGapsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationBooleanValue.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationBooleanValue.php
index 34ac211242..16b6eb663d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationBooleanValue.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationBooleanValue.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationTest.php
index ebd0b58ac1..3de53c7c7e 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DataValidationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFillTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFillTest.php
index dc61b95382..44fb8e57d9 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFillTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFillTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFontTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFontTest.php
index a4e94804bc..d000e36763 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFontTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DefaultFontTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DirectorySeparatorTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DirectorySeparatorTest.php
index e66c99e862..e90d599a10 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/DirectorySeparatorTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DirectorySeparatorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DrawingOneCellAnchorTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DrawingOneCellAnchorTest.php
index fe6b807860..b12b52e08c 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/DrawingOneCellAnchorTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DrawingOneCellAnchorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/EmptyFileTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/EmptyFileTest.php
index a2e78da4a9..2136b3a7a7 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/EmptyFileTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/EmptyFileTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/ExplicitDateTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/ExplicitDateTest.php
index 4f13264ffd..919e617aa7 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/ExplicitDateTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/ExplicitDateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenMergeCellsTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenMergeCellsTest.php
index 9d4fc81808..334a6d9299 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenMergeCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenMergeCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenWorksheetTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenWorksheetTest.php
index e11954eb51..b464cb6cfa 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenWorksheetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/HiddenWorksheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/HyperlinkTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/HyperlinkTest.php
index 81be815fa9..81bc5e1787 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/HyperlinkTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/HyperlinkTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/IgnoredErrorTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/IgnoredErrorTest.php
index bb476d6d69..aa0cbbc4b4 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/IgnoredErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/IgnoredErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/InvalidFileTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/InvalidFileTest.php
index 05acd8743c..95f49440b4 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/InvalidFileTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/InvalidFileTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue1482Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue1482Test.php
index 52536fc4cf..e1d0875504 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue1482Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue1482Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2301Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2301Test.php
index 7a5829f745..1d876a0ff8 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2301Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2301Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2331Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2331Test.php
index afa2ff5240..690c4e6f3b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2331Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2331Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use DateTimeZone;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2362Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2362Test.php
index 7efb04ad25..85e11a3572 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2362Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2362Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php
index 7e59418adf..c4ac64c39f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2387Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2450Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2450Test.php
index e6cb741bfa..4ec43f5745 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2450Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2450Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2488Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2488Test.php
index 9b77df4efd..6595cb5b42 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2488Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2488Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2490Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2490Test.php
index f65185e731..8307ce1db6 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2490Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2490Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2494Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2494Test.php
index ff400264fe..b691acd37c 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2494Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2494Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php
index 579582456d..011d00b8fb 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2501Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2516Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2516Test.php
index 13725418a1..e091d2a79d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2516Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2516Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2542Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2542Test.php
index ad9700014f..34027522fe 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2542Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2542Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2778Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2778Test.php
index 925b6fa4ff..b672f9c1c7 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2778Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2778Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2885Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2885Test.php
index 82727ef876..9f2783ce82 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2885Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue2885Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3126Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3126Test.php
index 2b8a5da701..8a1d3d7d1e 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3126Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3126Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3145Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3145Test.php
index b7d3a4cc71..df56d44bce 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3145Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3145Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3277Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3277Test.php
index 36804f4590..3ce7e7edfd 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3277Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3277Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3435Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3435Test.php
index 9d997dee39..0962724019 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3435Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3435Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3464Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3464Test.php
index 90a34f3d54..f466dc725d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3464Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3464Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3495Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3495Test.php
index b85d27e11e..5c0b71facf 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3495Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3495Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3534Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3534Test.php
index 72782ec25c..3a0146e74f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3534Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3534Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3552Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3552Test.php
index ee83d33bea..de3e738cc0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3552Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3552Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3553Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3553Test.php
index 4ae95b46eb..73c19f7e7e 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3553Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3553Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3613Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3613Test.php
index 71899039e4..fc2586643d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3613Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3613Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3665Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3665Test.php
index ba1778698e..f4990bc676 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3665Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3665Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3679ImgTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3679ImgTest.php
index 2b9559073f..5c9b380744 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3679ImgTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Issue3679ImgTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamedRangeTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamedRangeTest.php
index e4090d9832..380c6c2b8a 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamedRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamedRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceIssue2109bTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceIssue2109bTest.php
index b970f0844b..6c0e6b1e31 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceIssue2109bTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceIssue2109bTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceNonStdTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceNonStdTest.php
index cc2c03dce0..884454177c 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceNonStdTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceNonStdTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceOpenpyxl35Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceOpenpyxl35Test.php
index afb36862ac..d582530c62 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceOpenpyxl35Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceOpenpyxl35Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespacePurlTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespacePurlTest.php
index e8e9eaba3d..7d7ff3fe35 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespacePurlTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespacePurlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceStdTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceStdTest.php
index 5f8c8bc381..e859cc6a6f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceStdTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/NamespaceStdTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/OctothorpeTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/OctothorpeTest.php
index a5c6f20878..1fe65fb878 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/OctothorpeTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/OctothorpeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/OddColumnReadFilter.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/OddColumnReadFilter.php
index 859e5b56b3..f1e0c32795 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/OddColumnReadFilter.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/OddColumnReadFilter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -9,7 +11,7 @@
  */
 class OddColumnReadFilter implements IReadFilter
 {
-    public function readCell($columnAddress, $row, $worksheetName = '')
+    public function readCell($columnAddress, $row, $worksheetName = ''): bool
     {
         return (\ord(\substr($columnAddress, -1, 1)) % 2) === 1;
     }
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetup2Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetup2Test.php
index 12675b4181..7f31c7d3b1 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetup2Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetup2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetupTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetupTest.php
index 99a275e431..763dcfb07f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetupTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/PageSetupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/PropertiesTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/PropertiesTest.php
index bb414da562..9773a89fd0 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/PropertiesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/PropertiesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use DateTimeZone;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php
index 96e2003bcf..5d2713b799 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/RgbTintTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/RibbonTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/RibbonTest.php
index 68b3bb0146..6a47b27d5f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/RibbonTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/RibbonTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/RichTextTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/RichTextTest.php
index 8fb8baca6b..58a7ae1364 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/RichTextTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/RichTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/RowBreakTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/RowBreakTest.php
index 9bb75f6355..c98e1f5288 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/RowBreakTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/RowBreakTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/SharedFormulaTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/SharedFormulaTest.php
index 94f8e34923..b7e4532162 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/SharedFormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/SharedFormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetProtectionTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetProtectionTest.php
index 4f81521f72..123b39eb33 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetProtectionTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetProtectionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetsXlsxChartTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetsXlsxChartTest.php
index d47ce3114b..8af7f68543 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetsXlsxChartTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/SheetsXlsxChartTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Chart\DataSeries;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/SplitsTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/SplitsTest.php
index 424353a7a3..ddea4ae0cc 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/SplitsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/SplitsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/TableTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/TableTest.php
index 43f2e24c7d..a9a9b4e1c7 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/TableTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/TableTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/URLImageTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/URLImageTest.php
index e7f9901013..46698b2d61 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/URLImageTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/URLImageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/VerticalAlignTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/VerticalAlignTest.php
index 0d3c046768..2829a2dcf5 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/VerticalAlignTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/VerticalAlignTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/WorksheetInfoNamesTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/WorksheetInfoNamesTest.php
index 31f971a456..4c56339fb7 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/WorksheetInfoNamesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/WorksheetInfoNamesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/Xlsx2Test.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/Xlsx2Test.php
index 4f613f9f8a..9a9e1e26dc 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/Xlsx2Test.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/Xlsx2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxRootZipFilesTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxRootZipFilesTest.php
index 110c70b013..1142c0c80e 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxRootZipFilesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxRootZipFilesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxTest.php
index 8c4efd6d38..ab5081ccc6 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/XlsxTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Cell\Coordinate;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/DataValidationsTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/DataValidationsTest.php
index a90fc63e1c..151fc4235b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/DataValidationsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/DataValidationsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/PageSetupTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/PageSetupTest.php
index 26bb223c07..b5d8a33d54 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/PageSetupTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/PageSetupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/SplitsTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/SplitsTest.php
index 0fd49ca916..7f6b7f6fa6 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/SplitsTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/SplitsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlActiveSheetTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlActiveSheetTest.php
index 5df4feaa78..740efefe4d 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlActiveSheetTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlActiveSheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlColSpanTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlColSpanTest.php
index a78107fe88..05bd8f5be2 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlColSpanTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlColSpanTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlColumnRowHiddenTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlColumnRowHiddenTest.php
index b02f857e82..a17d27fb74 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlColumnRowHiddenTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlColumnRowHiddenTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlFilter.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlFilter.php
index b53fffd590..312550505b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlFilter.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlFilter.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\IReadFilter;
@@ -7,7 +9,7 @@
 /**  Define a Read Filter class implementing IReadFilter  */
 class XmlFilter implements IReadFilter
 {
-    public function readCell($columnAddress, $row, $worksheetName = '')
+    public function readCell($columnAddress, $row, $worksheetName = ''): bool
     {
         return $row !== 4;
     }
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlFontBoldItalicTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlFontBoldItalicTest.php
index 1465c99244..1328a4e083 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlFontBoldItalicTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlFontBoldItalicTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlFreezePanesTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlFreezePanesTest.php
index 440bbf50f0..b5645b7d37 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlFreezePanesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlFreezePanesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlInfoTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlInfoTest.php
index 9bab187792..623fc8be93 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlInfoTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlInfoTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlLoadTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlLoadTest.php
index 34716da13d..befac3b9ec 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlLoadTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlLoadTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use DateTimeZone;
@@ -15,8 +17,7 @@ class XmlLoadTest extends TestCase
     /** @var ?Spreadsheet */
     private $spreadsheet;
 
-    /** @var string */
-    private $locale;
+    private string $locale;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlOddTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlOddTest.php
index ace299c2c3..d479449cf7 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlOddTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlOddTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlPropertiesTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlPropertiesTest.php
index 8b4a225d3f..bcc23813e1 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlPropertiesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlPropertiesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlProtectionTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlProtectionTest.php
index acabb90fed..98f77eecf1 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlProtectionTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlProtectionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlStyleCoverageTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlStyleCoverageTest.php
index 7fd3f8e2ee..fa58c59b3f 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlStyleCoverageTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlStyleCoverageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlStylesTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlStylesTest.php
index df8f1418c3..837526325b 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlStylesTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlStylesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlTest.php
index e2e1a9ce0c..33dba13285 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Reader/Xml/XmlTopLeftTest.php b/tests/PhpSpreadsheetTests/Reader/Xml/XmlTopLeftTest.php
index 8320e83ec9..30cebca9e9 100644
--- a/tests/PhpSpreadsheetTests/Reader/Xml/XmlTopLeftTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Xml/XmlTopLeftTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Reader\Xml;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xml;
diff --git a/tests/PhpSpreadsheetTests/RefRangeTest.php b/tests/PhpSpreadsheetTests/RefRangeTest.php
index a05de9fd0a..17b4e3cd67 100644
--- a/tests/PhpSpreadsheetTests/RefRangeTest.php
+++ b/tests/PhpSpreadsheetTests/RefRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
@@ -9,11 +11,9 @@
 class RefRangeTest extends TestCase
 {
     /**
-     * @param int|string $expectedResult
-     *
      * @dataProvider providerRefRange
      */
-    public function testRefRange($expectedResult, string $rangeString): void
+    public function testRefRange(int|string $expectedResult, string $rangeString): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/ReferenceHelper2Test.php b/tests/PhpSpreadsheetTests/ReferenceHelper2Test.php
index 076ed1b6f3..c3f8484f05 100644
--- a/tests/PhpSpreadsheetTests/ReferenceHelper2Test.php
+++ b/tests/PhpSpreadsheetTests/ReferenceHelper2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/ReferenceHelper3Test.php b/tests/PhpSpreadsheetTests/ReferenceHelper3Test.php
index b1ee653fbe..4a437a0104 100644
--- a/tests/PhpSpreadsheetTests/ReferenceHelper3Test.php
+++ b/tests/PhpSpreadsheetTests/ReferenceHelper3Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/ReferenceHelperTest.php b/tests/PhpSpreadsheetTests/ReferenceHelperTest.php
index 05b3376f8e..90072d9b1a 100644
--- a/tests/PhpSpreadsheetTests/ReferenceHelperTest.php
+++ b/tests/PhpSpreadsheetTests/ReferenceHelperTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
@@ -224,7 +226,7 @@ public function testInsertRowsWithComments(): void
         $sheet->insertNewRowBefore(2, 2);
 
         $comments = array_map(
-            function (Comment $value) {
+            function (Comment $value): string {
                 return $value->getText()->getPlainText();
             },
             $sheet->getComments()
@@ -245,7 +247,7 @@ public function testDeleteRowsWithComments(): void
         $sheet->removeRow(2, 2);
 
         $comments = array_map(
-            function (Comment $value) {
+            function (Comment $value): string {
                 return $value->getText()->getPlainText();
             },
             $sheet->getComments()
diff --git a/tests/PhpSpreadsheetTests/RichTextTest.php b/tests/PhpSpreadsheetTests/RichTextTest.php
index 04a1d72a9e..3ebd099c0e 100644
--- a/tests/PhpSpreadsheetTests/RichTextTest.php
+++ b/tests/PhpSpreadsheetTests/RichTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
diff --git a/tests/PhpSpreadsheetTests/SettingsTest.php b/tests/PhpSpreadsheetTests/SettingsTest.php
index 146ddfe135..92668c96e3 100644
--- a/tests/PhpSpreadsheetTests/SettingsTest.php
+++ b/tests/PhpSpreadsheetTests/SettingsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpException;
diff --git a/tests/PhpSpreadsheetTests/Shared/CodePageTest.php b/tests/PhpSpreadsheetTests/Shared/CodePageTest.php
index dc74899757..ab3825eea4 100644
--- a/tests/PhpSpreadsheetTests/Shared/CodePageTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/CodePageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Exception;
@@ -10,11 +12,8 @@ class CodePageTest extends TestCase
 {
     /**
      * @dataProvider providerCodePage
-     *
-     * @param mixed $expectedResult
-     * @param mixed $codePageIndex
      */
-    public function testCodePageNumberToName($expectedResult, $codePageIndex): void
+    public function testCodePageNumberToName(mixed $expectedResult, mixed $codePageIndex): void
     {
         if ($expectedResult === 'exception') {
             $this->expectException(Exception::class);
diff --git a/tests/PhpSpreadsheetTests/Shared/Date2Test.php b/tests/PhpSpreadsheetTests/Shared/Date2Test.php
index 78d2b55ecd..7d66fe8717 100644
--- a/tests/PhpSpreadsheetTests/Shared/Date2Test.php
+++ b/tests/PhpSpreadsheetTests/Shared/Date2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Exception as CalculationException;
@@ -13,8 +15,7 @@ class Date2Test extends TestCase
     /** @var ?Spreadsheet */
     private $spreadsheet;
 
-    /** @var int */
-    private $calculateDateTimeType;
+    private int $calculateDateTimeType;
 
     protected function setUp(): void
     {
@@ -40,10 +41,9 @@ public function testInvalidType(): void
     /**
      * @dataProvider providerTimeOnly
      *
-     * @param float|int $expectedResult
      * @param float|int $value
      */
-    public function testTimeOnly($expectedResult, $value, ?string $format = null): void
+    public function testTimeOnly(int|float $expectedResult, int|float|string $value, ?string $format = null): void
     {
         Cell::setCalculateDateTimeType(Cell::CALCULATE_TIME_FLOAT);
         $this->spreadsheet = new Spreadsheet();
@@ -87,11 +87,8 @@ public static function providerTimeOnly(): array
 
     /**
      * @dataProvider providerDateAndTime
-     *
-     * @param float|int $expectedResult
-     * @param float|int $value
      */
-    public function testDateAndTime($expectedResult, $value, ?string $format = null): void
+    public function testDateAndTime(int|float $expectedResult, int|float|string $value, ?string $format = null): void
     {
         Cell::setCalculateDateTimeType(Cell::CALCULATE_DATE_TIME_FLOAT);
         $this->spreadsheet = new Spreadsheet();
@@ -135,11 +132,8 @@ public static function providerDateAndTime(): array
 
     /**
      * @dataProvider providerAsis
-     *
-     * @param float|int $expectedResult
-     * @param float|int $value
      */
-    public function testDefault($expectedResult, $value, ?string $format = null): void
+    public function testDefault(int|float $expectedResult, int|float|string $value, ?string $format = null): void
     {
         //Cell::setCalculateDateTimeType(Cell::CALCULATE_DATE_TIME_ASIS);
         $this->spreadsheet = new Spreadsheet();
@@ -160,11 +154,8 @@ public function testDefault($expectedResult, $value, ?string $format = null): vo
 
     /**
      * @dataProvider providerAsis
-     *
-     * @param float|int $expectedResult
-     * @param float|int $value
      */
-    public function testAsis($expectedResult, $value, ?string $format = null): void
+    public function testAsis(int|float $expectedResult, int|float|string $value, ?string $format = null): void
     {
         Cell::setCalculateDateTimeType(Cell::CALCULATE_DATE_TIME_ASIS);
         $this->spreadsheet = new Spreadsheet();
diff --git a/tests/PhpSpreadsheetTests/Shared/DateTest.php b/tests/PhpSpreadsheetTests/Shared/DateTest.php
index 9bcd6ff296..7839cfc452 100644
--- a/tests/PhpSpreadsheetTests/Shared/DateTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/DateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use DateTimeZone;
@@ -10,15 +12,9 @@
 
 class DateTest extends TestCase
 {
-    /**
-     * @var int
-     */
-    private $excelCalendar;
+    private int $excelCalendar;
 
-    /**
-     * @var null|DateTimeZone
-     */
-    private $dttimezone;
+    private ?DateTimeZone $dttimezone;
 
     protected function setUp(): void
     {
@@ -54,11 +50,8 @@ public function testSetExcelCalendarWithInvalidValue(): void
 
     /**
      * @dataProvider providerDateTimeExcelToTimestamp1900
-     *
-     * @param mixed $expectedResult
-     * @param mixed $excelDateTimeValue
      */
-    public function testDateTimeExcelToTimestamp1900($expectedResult, $excelDateTimeValue): void
+    public function testDateTimeExcelToTimestamp1900(mixed $expectedResult, mixed $excelDateTimeValue): void
     {
         if (is_numeric($expectedResult) && ($expectedResult > PHP_INT_MAX || $expectedResult < PHP_INT_MIN)) {
             self::markTestSkipped('Test invalid on 32-bit system.');
@@ -76,11 +69,8 @@ public static function providerDateTimeExcelToTimestamp1900(): array
 
     /**
      * @dataProvider providerDateTimeTimestampToExcel1900
-     *
-     * @param mixed $expectedResult
-     * @param mixed $unixTimestamp
      */
-    public function testDateTimeTimestampToExcel1900($expectedResult, $unixTimestamp): void
+    public function testDateTimeTimestampToExcel1900(mixed $expectedResult, mixed $unixTimestamp): void
     {
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
@@ -95,11 +85,8 @@ public static function providerDateTimeTimestampToExcel1900(): array
 
     /**
      * @dataProvider providerDateTimeDateTimeToExcel
-     *
-     * @param mixed $expectedResult
-     * @param mixed $dateTimeObject
      */
-    public function testDateTimeDateTimeToExcel($expectedResult, $dateTimeObject): void
+    public function testDateTimeDateTimeToExcel(mixed $expectedResult, mixed $dateTimeObject): void
     {
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
@@ -114,10 +101,8 @@ public static function providerDateTimeDateTimeToExcel(): array
 
     /**
      * @dataProvider providerDateTimeFormattedPHPToExcel1900
-     *
-     * @param mixed $expectedResult
      */
-    public function testDateTimeFormattedPHPToExcel1900($expectedResult, ...$args): void
+    public function testDateTimeFormattedPHPToExcel1900(mixed $expectedResult, mixed ...$args): void
     {
         Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
 
@@ -132,11 +117,8 @@ public static function providerDateTimeFormattedPHPToExcel1900(): array
 
     /**
      * @dataProvider providerDateTimeExcelToTimestamp1904
-     *
-     * @param mixed $expectedResult
-     * @param mixed $excelDateTimeValue
      */
-    public function testDateTimeExcelToTimestamp1904($expectedResult, $excelDateTimeValue): void
+    public function testDateTimeExcelToTimestamp1904(mixed $expectedResult, mixed $excelDateTimeValue): void
     {
         if (is_numeric($expectedResult) && ($expectedResult > PHP_INT_MAX || $expectedResult < PHP_INT_MIN)) {
             self::markTestSkipped('Test invalid on 32-bit system.');
@@ -154,11 +136,8 @@ public static function providerDateTimeExcelToTimestamp1904(): array
 
     /**
      * @dataProvider providerDateTimeTimestampToExcel1904
-     *
-     * @param mixed $expectedResult
-     * @param mixed $unixTimestamp
      */
-    public function testDateTimeTimestampToExcel1904($expectedResult, $unixTimestamp): void
+    public function testDateTimeTimestampToExcel1904(mixed $expectedResult, mixed $unixTimestamp): void
     {
         Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
 
@@ -173,10 +152,8 @@ public static function providerDateTimeTimestampToExcel1904(): array
 
     /**
      * @dataProvider providerIsDateTimeFormatCode
-     *
-     * @param mixed $expectedResult
      */
-    public function testIsDateTimeFormatCode($expectedResult, string $format): void
+    public function testIsDateTimeFormatCode(mixed $expectedResult, string $format): void
     {
         $result = Date::isDateTimeFormatCode($format);
         self::assertEquals($expectedResult, $result);
@@ -189,12 +166,8 @@ public static function providerIsDateTimeFormatCode(): array
 
     /**
      * @dataProvider providerDateTimeExcelToTimestamp1900Timezone
-     *
-     * @param mixed $expectedResult
-     * @param mixed $excelDateTimeValue
-     * @param mixed $timezone
      */
-    public function testDateTimeExcelToTimestamp1900Timezone($expectedResult, $excelDateTimeValue, $timezone): void
+    public function testDateTimeExcelToTimestamp1900Timezone(mixed $expectedResult, mixed $excelDateTimeValue, mixed $timezone): void
     {
         if (is_numeric($expectedResult) && ($expectedResult > PHP_INT_MAX || $expectedResult < PHP_INT_MIN)) {
             self::markTestSkipped('Test invalid on 32-bit system.');
diff --git a/tests/PhpSpreadsheetTests/Shared/DgContainerTest.php b/tests/PhpSpreadsheetTests/Shared/DgContainerTest.php
index 0a539f2845..57273bf665 100644
--- a/tests/PhpSpreadsheetTests/Shared/DgContainerTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/DgContainerTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Shared/DrawingTest.php b/tests/PhpSpreadsheetTests/Shared/DrawingTest.php
index 22cd1dbbc4..972576e605 100644
--- a/tests/PhpSpreadsheetTests/Shared/DrawingTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/DrawingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\Drawing;
diff --git a/tests/PhpSpreadsheetTests/Shared/ExactFontTest.php b/tests/PhpSpreadsheetTests/Shared/ExactFontTest.php
index b8573d3bf6..c5a3aa0d88 100644
--- a/tests/PhpSpreadsheetTests/Shared/ExactFontTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/ExactFontTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
@@ -36,17 +38,13 @@ class ExactFontTest extends TestCase
         ],
     ];
 
-    /** @var string */
-    private $holdDirectory;
+    private string $holdDirectory;
 
-    /** @var string */
-    private $holdAutoSizeMethod;
+    private string $holdAutoSizeMethod;
 
-    /** @var string */
-    private $directoryName = '';
+    private string $directoryName = '';
 
-    /** @var string */
-    private $incompleteMessage = '';
+    private string $incompleteMessage = '';
 
     private const KNOWN_MD5 = [
         '6a15e0a7c0367ba77a959ea27ebf11cf',
@@ -54,8 +52,7 @@ class ExactFontTest extends TestCase
         'be189a7e2711cdf2a7f6275c60cbc7e2',
     ];
 
-    /** @var null|float|int */
-    private $paddingAmountExact;
+    private float|int|null $paddingAmountExact;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Shared/FileTest.php b/tests/PhpSpreadsheetTests/Shared/FileTest.php
index cd040364a0..c4baf51ce2 100644
--- a/tests/PhpSpreadsheetTests/Shared/FileTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/FileTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
@@ -8,8 +10,7 @@
 
 class FileTest extends TestCase
 {
-    /** @var bool */
-    private $uploadFlag = false;
+    private bool $uploadFlag = false;
 
     /** @var string */
     private $tempfile = '';
diff --git a/tests/PhpSpreadsheetTests/Shared/Font2Test.php b/tests/PhpSpreadsheetTests/Shared/Font2Test.php
index adff9eba6c..2bfa429ef9 100644
--- a/tests/PhpSpreadsheetTests/Shared/Font2Test.php
+++ b/tests/PhpSpreadsheetTests/Shared/Font2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\Font;
diff --git a/tests/PhpSpreadsheetTests/Shared/Font3Test.php b/tests/PhpSpreadsheetTests/Shared/Font3Test.php
index e91e7acf08..b2801456dd 100644
--- a/tests/PhpSpreadsheetTests/Shared/Font3Test.php
+++ b/tests/PhpSpreadsheetTests/Shared/Font3Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Exception as SSException;
@@ -9,8 +11,7 @@
 
 class Font3Test extends TestCase
 {
-    /** @var string */
-    private $holdDirectory;
+    private string $holdDirectory;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Shared/FontFileNameTest.php b/tests/PhpSpreadsheetTests/Shared/FontFileNameTest.php
index 460a7851dd..bc0f0cf0b9 100644
--- a/tests/PhpSpreadsheetTests/Shared/FontFileNameTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/FontFileNameTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Exception as SSException;
@@ -12,11 +14,9 @@ class FontFileNameTest extends TestCase
     private const DEFAULT_DIRECTORY = 'tests/data/Shared/FakeFonts/Default';
     private const MAC_DIRECTORY = 'tests/data/Shared/FakeFonts/Mac';
 
-    /** @var string */
-    private $holdDirectory;
+    private string $holdDirectory;
 
-    /** @var array */
-    private $holdExtraFontArray;
+    private array $holdExtraFontArray;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Shared/FontTest.php b/tests/PhpSpreadsheetTests/Shared/FontTest.php
index 558c66f57a..27ebe43984 100644
--- a/tests/PhpSpreadsheetTests/Shared/FontTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/FontTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\Font;
@@ -41,11 +43,8 @@ public function testSetAutoSizeMethodWithInvalidValue(): void
 
     /**
      * @dataProvider providerFontSizeToPixels
-     *
-     * @param mixed $expectedResult
-     * @param mixed $size
      */
-    public function testFontSizeToPixels($expectedResult, $size): void
+    public function testFontSizeToPixels(mixed $expectedResult, mixed $size): void
     {
         $result = Font::fontSizeToPixels($size);
         self::assertEquals($expectedResult, $result);
@@ -58,11 +57,8 @@ public static function providerFontSizeToPixels(): array
 
     /**
      * @dataProvider providerInchSizeToPixels
-     *
-     * @param mixed $expectedResult
-     * @param mixed $size
      */
-    public function testInchSizeToPixels($expectedResult, $size): void
+    public function testInchSizeToPixels(mixed $expectedResult, mixed $size): void
     {
         $result = Font::inchSizeToPixels($size);
         self::assertEqualsWithDelta($expectedResult, $result, self::FONT_PRECISION);
@@ -75,11 +71,8 @@ public static function providerInchSizeToPixels(): array
 
     /**
      * @dataProvider providerCentimeterSizeToPixels
-     *
-     * @param mixed $expectedResult
-     * @param mixed $size
      */
-    public function testCentimeterSizeToPixels($expectedResult, $size): void
+    public function testCentimeterSizeToPixels(mixed $expectedResult, mixed $size): void
     {
         $result = Font::centimeterSizeToPixels($size);
         self::assertEqualsWithDelta($expectedResult, $result, self::FONT_PRECISION);
diff --git a/tests/PhpSpreadsheetTests/Shared/OLEPhpunit10Test.php b/tests/PhpSpreadsheetTests/Shared/OLEPhpunit10Test.php
index 2bf88b3ff3..7b97a979d2 100644
--- a/tests/PhpSpreadsheetTests/Shared/OLEPhpunit10Test.php
+++ b/tests/PhpSpreadsheetTests/Shared/OLEPhpunit10Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\OLE;
@@ -14,8 +16,7 @@
  */
 class OLEPhpunit10Test extends TestCase
 {
-    /** @var string */
-    private static $errorString;
+    private static string $errorString;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Shared/OLEReadTest.php b/tests/PhpSpreadsheetTests/Shared/OLEReadTest.php
index 7fe485c9cc..0790146658 100644
--- a/tests/PhpSpreadsheetTests/Shared/OLEReadTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/OLEReadTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\OLERead;
diff --git a/tests/PhpSpreadsheetTests/Shared/OLETest.php b/tests/PhpSpreadsheetTests/Shared/OLETest.php
index db81272c55..f4fe368d4f 100644
--- a/tests/PhpSpreadsheetTests/Shared/OLETest.php
+++ b/tests/PhpSpreadsheetTests/Shared/OLETest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
diff --git a/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php b/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php
index 97e63deab9..78a89386c1 100644
--- a/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/PasswordHasherTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpException;
diff --git a/tests/PhpSpreadsheetTests/Shared/PasswordReloadTest.php b/tests/PhpSpreadsheetTests/Shared/PasswordReloadTest.php
index 14007416e8..50b5b1f93c 100644
--- a/tests/PhpSpreadsheetTests/Shared/PasswordReloadTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/PasswordReloadTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\PasswordHasher;
diff --git a/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php b/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php
index 5467949993..5ee0953773 100644
--- a/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
diff --git a/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php b/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php
index bcbcd5d215..e77e02a424 100644
--- a/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/StringHelperTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
@@ -7,20 +9,11 @@
 
 class StringHelperTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $currencyCode;
-
-    /**
-     * @var string
-     */
-    private $decimalSeparator;
-
-    /**
-     * @var string
-     */
-    private $thousandsSeparator;
+    private string $currencyCode;
+
+    private string $decimalSeparator;
+
+    private string $thousandsSeparator;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php b/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php
index 3db13b25c2..ec42f59ceb 100644
--- a/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/TimeZoneTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use DateTime;
@@ -10,15 +12,9 @@
 
 class TimeZoneTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $tztimezone;
+    private string $tztimezone;
 
-    /**
-     * @var null|DateTimeZone
-     */
-    private $dttimezone;
+    private ?DateTimeZone $dttimezone;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Shared/Trend/ExponentialBestFitTest.php b/tests/PhpSpreadsheetTests/Shared/Trend/ExponentialBestFitTest.php
index f17785a615..ec44ff4c02 100644
--- a/tests/PhpSpreadsheetTests/Shared/Trend/ExponentialBestFitTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/Trend/ExponentialBestFitTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared\Trend;
 
 use PhpOffice\PhpSpreadsheet\Shared\Trend\ExponentialBestFit;
@@ -9,21 +11,14 @@ class ExponentialBestFitTest extends TestCase
 {
     /**
      * @dataProvider providerExponentialBestFit
-     *
-     * @param mixed $expectedSlope
-     * @param mixed $expectedIntersect
-     * @param mixed $expectedGoodnessOfFit
-     * @param mixed $yValues
-     * @param mixed $xValues
-     * @param mixed $expectedEquation
      */
     public function testExponentialBestFit(
-        $expectedSlope,
-        $expectedIntersect,
-        $expectedGoodnessOfFit,
-        $expectedEquation,
-        $yValues,
-        $xValues
+        mixed $expectedSlope,
+        mixed $expectedIntersect,
+        mixed $expectedGoodnessOfFit,
+        mixed $expectedEquation,
+        mixed $yValues,
+        mixed $xValues
     ): void {
         $bestFit = new ExponentialBestFit($yValues, $xValues);
         $slope = $bestFit->getSlope(1);
diff --git a/tests/PhpSpreadsheetTests/Shared/Trend/LinearBestFitTest.php b/tests/PhpSpreadsheetTests/Shared/Trend/LinearBestFitTest.php
index c88ff8d58a..6f150ffa96 100644
--- a/tests/PhpSpreadsheetTests/Shared/Trend/LinearBestFitTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/Trend/LinearBestFitTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared\Trend;
 
 use PhpOffice\PhpSpreadsheet\Shared\Trend\LinearBestFit;
@@ -11,21 +13,14 @@ class LinearBestFitTest extends TestCase
 
     /**
      * @dataProvider providerLinearBestFit
-     *
-     * @param mixed $expectedSlope
-     * @param mixed $expectedIntersect
-     * @param mixed $expectedGoodnessOfFit
-     * @param mixed $yValues
-     * @param mixed $xValues
-     * @param mixed $expectedEquation
      */
     public function testLinearBestFit(
-        $expectedSlope,
-        $expectedIntersect,
-        $expectedGoodnessOfFit,
-        $expectedEquation,
-        $yValues,
-        $xValues
+        mixed $expectedSlope,
+        mixed $expectedIntersect,
+        mixed $expectedGoodnessOfFit,
+        mixed $expectedEquation,
+        mixed $yValues,
+        mixed $xValues
     ): void {
         $bestFit = new LinearBestFit($yValues, $xValues);
         $slope = $bestFit->getSlope(1);
diff --git a/tests/PhpSpreadsheetTests/Shared/XmlWriterTest.php b/tests/PhpSpreadsheetTests/Shared/XmlWriterTest.php
index 200325137b..63bebc34d9 100644
--- a/tests/PhpSpreadsheetTests/Shared/XmlWriterTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/XmlWriterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Shared;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
@@ -8,8 +10,7 @@
 
 class XmlWriterTest extends TestCase
 {
-    /** @var bool */
-    private $debugEnabled;
+    private bool $debugEnabled;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/SpreadsheetCoverageTest.php b/tests/PhpSpreadsheetTests/SpreadsheetCoverageTest.php
index 54febf7b9d..196dabd336 100644
--- a/tests/PhpSpreadsheetTests/SpreadsheetCoverageTest.php
+++ b/tests/PhpSpreadsheetTests/SpreadsheetCoverageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Exception as SSException;
diff --git a/tests/PhpSpreadsheetTests/SpreadsheetTest.php b/tests/PhpSpreadsheetTests/SpreadsheetTest.php
index 5c61eaf2ea..fe4e986439 100644
--- a/tests/PhpSpreadsheetTests/SpreadsheetTest.php
+++ b/tests/PhpSpreadsheetTests/SpreadsheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/AlignmentMiddleTest.php b/tests/PhpSpreadsheetTests/Style/AlignmentMiddleTest.php
index 1d260a6e58..2fcb719185 100644
--- a/tests/PhpSpreadsheetTests/Style/AlignmentMiddleTest.php
+++ b/tests/PhpSpreadsheetTests/Style/AlignmentMiddleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Style/AlignmentTest.php b/tests/PhpSpreadsheetTests/Style/AlignmentTest.php
index 6f50ce2252..0f0ba5e15d 100644
--- a/tests/PhpSpreadsheetTests/Style/AlignmentTest.php
+++ b/tests/PhpSpreadsheetTests/Style/AlignmentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php b/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php
index aec5520d93..926dcb22eb 100644
--- a/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Style/BorderTest.php b/tests/PhpSpreadsheetTests/Style/BorderTest.php
index cf6cd3a964..9f18f07668 100644
--- a/tests/PhpSpreadsheetTests/Style/BorderTest.php
+++ b/tests/PhpSpreadsheetTests/Style/BorderTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Style/ColorIndexTest.php b/tests/PhpSpreadsheetTests/Style/ColorIndexTest.php
index 2913f3f5b5..31d980ebd3 100644
--- a/tests/PhpSpreadsheetTests/Style/ColorIndexTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ColorIndexTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx\Styles;
diff --git a/tests/PhpSpreadsheetTests/Style/ColorTest.php b/tests/PhpSpreadsheetTests/Style/ColorTest.php
index b4d4b1fe37..4848f5cf98 100644
--- a/tests/PhpSpreadsheetTests/Style/ColorTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ColorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Style\Color;
@@ -76,10 +78,8 @@ public function testRGBFromArray(): void
 
     /**
      * @dataProvider providerColorGetRed
-     *
-     * @param mixed $expectedResult
      */
-    public function testGetRed($expectedResult, string $color, ?bool $bool = null): void
+    public function testGetRed(mixed $expectedResult, string $color, ?bool $bool = null): void
     {
         if ($bool === null) {
             $result = Color::getRed($color);
@@ -96,10 +96,8 @@ public static function providerColorGetRed(): array
 
     /**
      * @dataProvider providerColorGetGreen
-     *
-     * @param mixed $expectedResult
      */
-    public function testGetGreen($expectedResult, string $color, ?bool $bool = null): void
+    public function testGetGreen(mixed $expectedResult, string $color, ?bool $bool = null): void
     {
         if ($bool === null) {
             $result = Color::getGreen($color);
@@ -116,10 +114,8 @@ public static function providerColorGetGreen(): array
 
     /**
      * @dataProvider providerColorGetBlue
-     *
-     * @param mixed $expectedResult
      */
-    public function testGetBlue($expectedResult, string $color, ?bool $bool = null): void
+    public function testGetBlue(mixed $expectedResult, string $color, ?bool $bool = null): void
     {
         if ($bool === null) {
             $result = Color::getBlue($color);
@@ -136,10 +132,8 @@ public static function providerColorGetBlue(): array
 
     /**
      * @dataProvider providerColorChangeBrightness
-     *
-     * @param mixed $expectedResult
      */
-    public function testChangeBrightness($expectedResult, ...$args): void
+    public function testChangeBrightness(mixed $expectedResult, mixed ...$args): void
     {
         $result = Color::changeBrightness(...$args);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalBoolTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalBoolTest.php
index 2e50fcedb8..e4b0c7fcf8 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalBoolTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalBoolTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/CellMatcherTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/CellMatcherTest.php
index 84e5dcd297..505991d4e4 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/CellMatcherTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/CellMatcherTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/BlankWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/BlankWizardTest.php
index 025376d9b6..027c0674eb 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/BlankWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/BlankWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/CellValueWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/CellValueWizardTest.php
index fa98db447f..7ccc860fc0 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/CellValueWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/CellValueWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
@@ -33,11 +35,8 @@ protected function setUp(): void
 
     /**
      * @dataProvider basicCellValueDataProvider
-     *
-     * @param mixed $operand
-     * @param mixed $expectedCondition
      */
-    public function testBasicCellValueWizard(string $operator, $operand, string $expectedOperator, $expectedCondition): void
+    public function testBasicCellValueWizard(string $operator, mixed $operand, string $expectedOperator, mixed $expectedCondition): void
     {
         $ruleType = Wizard::CELL_VALUE;
         /** @var Wizard\CellValue $wizard */
@@ -75,11 +74,8 @@ public static function basicCellValueDataProvider(): array
 
     /**
      * @dataProvider relativeCellValueDataProvider
-     *
-     * @param mixed $operand
-     * @param mixed $expectedCondition
      */
-    public function testRelativeCellValueWizard($operand, $expectedCondition): void
+    public function testRelativeCellValueWizard(mixed $operand, mixed $expectedCondition): void
     {
         $ruleType = Wizard::CELL_VALUE;
         /** @var Wizard\CellValue $wizard */
@@ -109,11 +105,8 @@ public static function relativeCellValueDataProvider(): array
 
     /**
      * @dataProvider formulaCellValueDataProvider
-     *
-     * @param mixed $operand
-     * @param mixed $expectedCondition
      */
-    public function testCellValueWizardWithFormula($operand, $expectedCondition): void
+    public function testCellValueWizardWithFormula(mixed $operand, mixed $expectedCondition): void
     {
         $ruleType = Wizard::CELL_VALUE;
         /** @var Wizard\CellValue $wizard */
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DateValueWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DateValueWizardTest.php
index 175dc03c22..824066cb98 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DateValueWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DateValueWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DuplicatesWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DuplicatesWizardTest.php
index c6ed6e034a..2b280a7aad 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DuplicatesWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/DuplicatesWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ErrorWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ErrorWizardTest.php
index f58b90e452..b845318fe3 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ErrorWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ErrorWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ExpressionWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ExpressionWizardTest.php
index 6b6547eb8b..7ce0c2be01 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ExpressionWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/ExpressionWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/TextValueWizardTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/TextValueWizardTest.php
index 505e3d7c78..de6d22aafa 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/TextValueWizardTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/TextValueWizardTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php
index 06b900c07e..b3ddc9b663 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\ConditionalFormatting\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalTest.php
index 064a52f187..e29043166a 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Style\Conditional;
diff --git a/tests/PhpSpreadsheetTests/Style/ExportArrayTest.php b/tests/PhpSpreadsheetTests/Style/ExportArrayTest.php
index a062b4cf6b..5709d5c0a2 100644
--- a/tests/PhpSpreadsheetTests/Style/ExportArrayTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ExportArrayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Style/FillTest.php b/tests/PhpSpreadsheetTests/Style/FillTest.php
index 18ee224dcc..f55b681103 100644
--- a/tests/PhpSpreadsheetTests/Style/FillTest.php
+++ b/tests/PhpSpreadsheetTests/Style/FillTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Style\Color;
diff --git a/tests/PhpSpreadsheetTests/Style/FontTest.php b/tests/PhpSpreadsheetTests/Style/FontTest.php
index 6cd4d950c7..20df75b1a5 100644
--- a/tests/PhpSpreadsheetTests/Style/FontTest.php
+++ b/tests/PhpSpreadsheetTests/Style/FontTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/AccountingTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/AccountingTest.php
index 269ecdcdca..a71153bd42 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/AccountingTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/AccountingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use NumberFormatter;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/CurrencyTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/CurrencyTest.php
index a84d5566d1..dd37d2fe39 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/CurrencyTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/CurrencyTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use NumberFormatter;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTest.php
index e4b83a0b55..cc19a4129e 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat\Wizard\Date;
@@ -13,7 +15,7 @@ class DateTest extends TestCase
      * @param null|string|string[] $separators
      * @param string[] $formatBlocks
      */
-    public function testDate(string $expectedResult, $separators = null, array $formatBlocks = []): void
+    public function testDate(string $expectedResult, string|array|null $separators = null, array $formatBlocks = []): void
     {
         $wizard = new Date($separators, ...$formatBlocks);
         self::assertSame($expectedResult, (string) $wizard);
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTimeTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTimeTest.php
index a92ae6d065..17fedffa3b 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTimeTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DateTimeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat\Wizard\Date;
@@ -15,7 +17,7 @@ class DateTimeTest extends TestCase
      * @param null|string|string[] $separators
      * @param string[] $formatBlocks
      */
-    public function testDateTime(string $expectedResult, $separators, array $formatBlocks): void
+    public function testDateTime(string $expectedResult, string|null|array $separators, array $formatBlocks): void
     {
         $wizard = new DateTime($separators, ...$formatBlocks);
         self::assertSame($expectedResult, (string) $wizard);
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DurationTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DurationTest.php
index 90cbdf68d9..0804deee02 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DurationTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/DurationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat\Wizard\Duration;
@@ -13,7 +15,7 @@ class DurationTest extends TestCase
      * @param null|string|string[] $separators
      * @param string[] $formatBlocks
      */
-    public function testTime(string $expectedResult, $separators = null, array $formatBlocks = []): void
+    public function testTime(string $expectedResult, string|array|null $separators = null, array $formatBlocks = []): void
     {
         $wizard = new Duration($separators, ...$formatBlocks);
         self::assertSame($expectedResult, (string) $wizard);
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/NumberTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/NumberTest.php
index 9f9a51a59d..950496ed45 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/NumberTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/NumberTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use NumberFormatter;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/PercentageTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/PercentageTest.php
index 913801b892..23f45b9c95 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/PercentageTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/PercentageTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use NumberFormatter;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/ScientificTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/ScientificTest.php
index 5f17046954..9120284c61 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/ScientificTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/ScientificTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use NumberFormatter;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/TimeTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/TimeTest.php
index a8e986cf98..de86ffe96d 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/TimeTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormat/Wizard/TimeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style\NumberFormat\Wizard;
 
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat\Wizard\Time;
@@ -13,7 +15,7 @@ class TimeTest extends TestCase
      * @param null|string|string[] $separators
      * @param string[] $formatBlocks
      */
-    public function testTime(string $expectedResult, $separators = null, array $formatBlocks = []): void
+    public function testTime(string $expectedResult, string|array|null $separators = null, array $formatBlocks = []): void
     {
         $wizard = new Time($separators, ...$formatBlocks);
         self::assertSame($expectedResult, (string) $wizard);
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormatBuiltinTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormatBuiltinTest.php
index dd3d672ae9..5e33ff3146 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormatBuiltinTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormatBuiltinTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormatRoundTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormatRoundTest.php
index 3401b02015..646c7f4f0d 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormatRoundTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormatRoundTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php
index 741d36e7d8..5cd09574c8 100644
--- a/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormatTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
@@ -9,20 +11,11 @@
 
 class NumberFormatTest extends TestCase
 {
-    /**
-     * @var string
-     */
-    private $currencyCode;
+    private string $currencyCode;
 
-    /**
-     * @var string
-     */
-    private $decimalSeparator;
+    private string $decimalSeparator;
 
-    /**
-     * @var string
-     */
-    private $thousandsSeparator;
+    private string $thousandsSeparator;
 
     protected function setUp(): void
     {
@@ -42,10 +35,8 @@ protected function tearDown(): void
 
     /**
      * @dataProvider providerNumberFormat
-     *
-     * @param mixed $expectedResult
      */
-    public function testFormatValueWithMask($expectedResult, ...$args): void
+    public function testFormatValueWithMask(mixed $expectedResult, mixed ...$args): void
     {
         $result = NumberFormat::toFormattedString(...$args);
         self::assertSame($expectedResult, $result);
@@ -58,11 +49,8 @@ public static function providerNumberFormat(): array
 
     /**
      * @dataProvider providerNumberFormatFractions
-     *
-     * @param mixed $expectedResult
-     * @param mixed $args
      */
-    public function testFormatValueWithMaskFraction($expectedResult, ...$args): void
+    public function testFormatValueWithMaskFraction(mixed $expectedResult, mixed ...$args): void
     {
         $result = NumberFormat::toFormattedString(...$args);
         self::assertEquals($expectedResult, $result);
@@ -75,11 +63,8 @@ public static function providerNumberFormatFractions(): array
 
     /**
      * @dataProvider providerNumberFormatDates
-     *
-     * @param mixed $expectedResult
-     * @param mixed $args
      */
-    public function testFormatValueWithMaskDate($expectedResult, ...$args): void
+    public function testFormatValueWithMaskDate(mixed $expectedResult, mixed ...$args): void
     {
         $result = NumberFormat::toFormattedString(...$args);
         self::assertEquals($expectedResult, $result);
diff --git a/tests/PhpSpreadsheetTests/Style/StyleTest.php b/tests/PhpSpreadsheetTests/Style/StyleTest.php
index 13998546aa..be67a5e792 100644
--- a/tests/PhpSpreadsheetTests/Style/StyleTest.php
+++ b/tests/PhpSpreadsheetTests/Style/StyleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Style;
 
 use PhpOffice\PhpSpreadsheet\Cell\CellAddress;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterAverageTop10Test.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterAverageTop10Test.php
index 1e82746906..55c80dfc60 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterAverageTop10Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterAverageTop10Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomNumericTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomNumericTest.php
index 72a3d1a6b1..e36135a6cb 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomNumericTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomNumericTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomTextTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomTextTest.php
index a40797b775..dcaba9ef3c 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomTextTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterCustomTextTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterMonthTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterMonthTest.php
index 480803d8eb..742e6cbc3b 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterMonthTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterMonthTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterQuarterTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterQuarterTest.php
index 9fd1a5b0de..20fd146b22 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterQuarterTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterQuarterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTest.php
index ebec36864c..7b1583d545 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTodayTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTodayTest.php
index 588316ed2d..dfe8b57400 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTodayTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterTodayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterWeekTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterWeekTest.php
index 8b1d412364..cbd5379e94 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterWeekTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterWeekTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterYearTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterYearTest.php
index 4baa8dc050..84316d2d5e 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterYearTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/AutoFilterYearTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use DateTimeImmutable;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php
index c94cb3a4b4..4e7e483482 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/ColumnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DateGroupTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DateGroupTest.php
index a89ebd5b53..dc02ca7b8b 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DateGroupTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DateGroupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DeleteAutoFilterTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DeleteAutoFilterTest.php
index f1ef1aca3b..6fd7019dc7 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DeleteAutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/DeleteAutoFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 class DeleteAutoFilterTest extends SetupTeardown
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleCustomTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleCustomTest.php
index bffd885e46..7f643e8edb 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleCustomTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleCustomTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\AutoFilter\Column;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleDateGroupTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleDateGroupTest.php
index 3a32a9ebfd..d09ce649ea 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleDateGroupTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleDateGroupTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleTest.php
index c9eaa4f2e7..0ab5ca2349 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/RuleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/SetupTeardown.php b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/SetupTeardown.php
index c77cf7f881..925c97c462 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/SetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoFilter/SetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\AutoFilter;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php
index e774b04cc2..4a4f488bb3 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowTest.php b/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowTest.php
index 48a04685b8..14ef832e5d 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowUndeprecatedTest.php b/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowUndeprecatedTest.php
index 630cf1db12..40f1d03e2d 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowUndeprecatedTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ByColumnAndRowUndeprecatedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIterator2Test.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIterator2Test.php
index 88f1e7d7c8..894a8adf7a 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIterator2Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIterator2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
index 02b9642656..593d7f1497 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnCellIteratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnDimension2Test.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnDimension2Test.php
index f5878eef56..e65c003e84 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnDimension2Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnDimension2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Helper\Dimension;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnDimensionTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnDimensionTest.php
index 1994fa81a5..ee5cc92ed2 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnDimensionTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnDimensionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Helper\Dimension;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorEmptyTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorEmptyTest.php
index 47c403729b..b1e0f07a7b 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorEmptyTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorEmptyTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php
index 7bb20cd620..8182992eef 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnIteratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception as Except;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ColumnTest.php b/tests/PhpSpreadsheetTests/Worksheet/ColumnTest.php
index 0e265156f3..b2c0b7515f 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ColumnTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ColumnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ConditionalStyleTest.php b/tests/PhpSpreadsheetTests/Worksheet/ConditionalStyleTest.php
index 6221fee4b8..e884740391 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ConditionalStyleTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ConditionalStyleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/DefaultPaperSizeTest.php b/tests/PhpSpreadsheetTests/Worksheet/DefaultPaperSizeTest.php
index 5ab3c2825d..b309bef023 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/DefaultPaperSizeTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/DefaultPaperSizeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -8,11 +10,9 @@
 
 class DefaultPaperSizeTest extends TestCase
 {
-    /** @var int */
-    private $paperSize;
+    private int $paperSize;
 
-    /** @var string */
-    private $orientation;
+    private string $orientation;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Worksheet/DrawingTest.php b/tests/PhpSpreadsheetTests/Worksheet/DrawingTest.php
index 17e17e1923..4ab1ca2e29 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/DrawingTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/DrawingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/IteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/IteratorTest.php
index b2a063439d..cf3eca54e3 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/IteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/IteratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/MemoryDrawingTest.php b/tests/PhpSpreadsheetTests/Worksheet/MemoryDrawingTest.php
index dd992dae1c..3074961436 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/MemoryDrawingTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/MemoryDrawingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use GdImage;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/MergeBehaviourTest.php b/tests/PhpSpreadsheetTests/Worksheet/MergeBehaviourTest.php
index ab79ad8302..7f0b04df64 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/MergeBehaviourTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/MergeBehaviourTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/PageBreakTest.php b/tests/PhpSpreadsheetTests/Worksheet/PageBreakTest.php
index cbeb96d68d..a211e2ad75 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/PageBreakTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/PageBreakTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\CellAddress;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/PageMarginsTest.php b/tests/PhpSpreadsheetTests/Worksheet/PageMarginsTest.php
index 084e6f786c..f6795fc99c 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/PageMarginsTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/PageMarginsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\PageMargins;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/ProtectionTest.php b/tests/PhpSpreadsheetTests/Worksheet/ProtectionTest.php
index 0be172b0e0..8f1e2733d6 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/ProtectionTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/ProtectionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Protection;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RemoveTest.php b/tests/PhpSpreadsheetTests/Worksheet/RemoveTest.php
index 73c04c0717..0dcab2d10d 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RemoveTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RemoveTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\Coordinate;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowCellIterator2Test.php b/tests/PhpSpreadsheetTests/Worksheet/RowCellIterator2Test.php
index 4b5f624e86..1f3e883e23 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowCellIterator2Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowCellIterator2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
index 9afda3cb91..09578ffb75 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowCellIteratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\Cell;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowDimensionSaveTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowDimensionSaveTest.php
index ab09de26e1..8bce187936 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowDimensionSaveTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowDimensionSaveTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowDimensionTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowDimensionTest.php
index a5b5a04d00..1782ba52fb 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowDimensionTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowDimensionTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Helper\Dimension;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowIteratorEmptyTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowIteratorEmptyTest.php
index ec062a032f..1d8a83caf9 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowIteratorEmptyTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowIteratorEmptyTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php
index 3ba3654e41..2ddc9fb6c0 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowIteratorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception as Except;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/RowTest.php b/tests/PhpSpreadsheetTests/Worksheet/RowTest.php
index dd0eb78fc6..810e763d42 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/RowTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/RowTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/SheetViewTest.php b/tests/PhpSpreadsheetTests/Worksheet/SheetViewTest.php
index f37c79581d..38926181f2 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/SheetViewTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/SheetViewTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/ColumnTest.php b/tests/PhpSpreadsheetTests/Worksheet/Table/ColumnTest.php
index c7edd86a0c..be184af1bf 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/ColumnTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/ColumnTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/FormulaTest.php b/tests/PhpSpreadsheetTests/Worksheet/Table/FormulaTest.php
index 25dc27025a..4faba0bee1 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/FormulaTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/FormulaTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3635Test.php b/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3635Test.php
index d004d8d8b8..ed687e14dd 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3635Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3635Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Table;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3659Test.php b/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3659Test.php
index fcb4c6487d..3ec7c6bd5f 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3659Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/Issue3659Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Table;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/RemoveTableTest.php b/tests/PhpSpreadsheetTests/Worksheet/Table/RemoveTableTest.php
index fb2bb93979..be46b663de 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/RemoveTableTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/RemoveTableTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Table;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/SetupTeardown.php b/tests/PhpSpreadsheetTests/Worksheet/Table/SetupTeardown.php
index 76e914f7db..41bf86ed23 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/SetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/SetupTeardown.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/TableStyleTest.php b/tests/PhpSpreadsheetTests/Worksheet/Table/TableStyleTest.php
index 830cc87b82..a84da3814d 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/TableStyleTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/TableStyleTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Table;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Table/TableTest.php b/tests/PhpSpreadsheetTests/Worksheet/Table/TableTest.php
index 5ff0daed12..33acde1259 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Table/TableTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Table/TableTest.php
@@ -1,7 +1,10 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet\Table;
 
+use PhpOffice\PhpSpreadsheet\Cell\AddressRange;
 use PhpOffice\PhpSpreadsheet\Cell\CellAddress;
 use PhpOffice\PhpSpreadsheet\Cell\CellRange;
 use PhpOffice\PhpSpreadsheet\Exception as PhpSpreadsheetException;
@@ -154,9 +157,8 @@ public function testGetRange(): void
 
     /**
      * @param AddressRange|array<int>|string $fullRange
-     * @param string $fullRange
      */
-    public function xtestSetRangeValidRange($fullRange, string $actualRange): void
+    public function xtestSetRangeValidRange(string|array|AddressRange $fullRange, string $actualRange): void
     {
         $table = new Table(self::INITIAL_RANGE);
 
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Worksheet2Test.php b/tests/PhpSpreadsheetTests/Worksheet/Worksheet2Test.php
index 2b1a2b5d82..8735caccd1 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Worksheet2Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Worksheet2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpreadsheetException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/Worksheet3Test.php b/tests/PhpSpreadsheetTests/Worksheet/Worksheet3Test.php
index 04320cb832..addd0f2ef8 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/Worksheet3Test.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/Worksheet3Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/WorksheetNamedRangesTest.php b/tests/PhpSpreadsheetTests/Worksheet/WorksheetNamedRangesTest.php
index 3b7f64c577..67777ad6ce 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/WorksheetNamedRangesTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/WorksheetNamedRangesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/WorksheetParentTest.php b/tests/PhpSpreadsheetTests/Worksheet/WorksheetParentTest.php
index 2a66340676..b5960ea30e 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/WorksheetParentTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/WorksheetParentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use PhpOffice\PhpSpreadsheet\Exception as SpException;
diff --git a/tests/PhpSpreadsheetTests/Worksheet/WorksheetTest.php b/tests/PhpSpreadsheetTests/Worksheet/WorksheetTest.php
index bd6c25a33d..87e7eab612 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/WorksheetTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/WorksheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Worksheet;
 
 use Exception;
@@ -33,12 +35,9 @@ public static function setTitleInvalidProvider(): array
     }
 
     /**
-     * @param string $title
-     * @param string $expectMessage
-     *
      * @dataProvider setTitleInvalidProvider
      */
-    public function testSetTitleInvalid($title, $expectMessage): void
+    public function testSetTitleInvalid(string $title, string $expectMessage): void
     {
         // First, test setting title with validation disabled -- should be successful
         $worksheet = new Worksheet();
@@ -93,12 +92,9 @@ public static function setCodeNameInvalidProvider(): array
     }
 
     /**
-     * @param string $codeName
-     * @param string $expectMessage
-     *
      * @dataProvider setCodeNameInvalidProvider
      */
-    public function testSetCodeNameInvalid($codeName, $expectMessage): void
+    public function testSetCodeNameInvalid(string $codeName, string $expectMessage): void
     {
         // First, test setting code name with validation disabled -- should be successful
         $worksheet = new Worksheet();
@@ -156,14 +152,9 @@ public static function extractSheetTitleProvider(): array
     }
 
     /**
-     * @param string $range
-     * @param string $expectTitle
-     * @param string $expectCell
-     * @param string $expectCell2
-     *
      * @dataProvider extractSheetTitleProvider
      */
-    public function testExtractSheetTitle($range, $expectTitle, $expectCell, $expectCell2): void
+    public function testExtractSheetTitle(string $range, string $expectTitle, string $expectCell, string $expectCell2): void
     {
         // only cell reference
         self::assertSame($expectCell, Worksheet::extractSheetTitle($range));
@@ -618,7 +609,7 @@ public function testRangeToArrayWithCellRangeObject(array $expected, string $fro
 
         $cellRange = new CellRange(new CellAddress($fromCell), new CellAddress($toCell));
 
-        self::assertSame($expected, $worksheet->rangeToArray($cellRange));
+        self::assertSame($expected, $worksheet->rangeToArray((string) $cellRange));
     }
 
     public static function rangeToArrayProvider(): array
diff --git a/tests/PhpSpreadsheetTests/Writer/Csv/CsvEnclosureTest.php b/tests/PhpSpreadsheetTests/Writer/Csv/CsvEnclosureTest.php
index 383f83abac..ffbdf453c1 100644
--- a/tests/PhpSpreadsheetTests/Writer/Csv/CsvEnclosureTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Csv/CsvEnclosureTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv as CsvReader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Csv/CsvExcelCompatibilityTest.php b/tests/PhpSpreadsheetTests/Writer/Csv/CsvExcelCompatibilityTest.php
index 9b7d16aae2..7330ae8698 100644
--- a/tests/PhpSpreadsheetTests/Writer/Csv/CsvExcelCompatibilityTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Csv/CsvExcelCompatibilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv as CsvReader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Csv/CsvOutputEncodingTest.php b/tests/PhpSpreadsheetTests/Writer/Csv/CsvOutputEncodingTest.php
index 81e4428e29..41562a5852 100644
--- a/tests/PhpSpreadsheetTests/Writer/Csv/CsvOutputEncodingTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Csv/CsvOutputEncodingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Csv;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Csv/CsvWriteTest.php b/tests/PhpSpreadsheetTests/Writer/Csv/CsvWriteTest.php
index aa9a8fc372..a45b2da7f5 100644
--- a/tests/PhpSpreadsheetTests/Writer/Csv/CsvWriteTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Csv/CsvWriteTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Csv;
 
 use PhpOffice\PhpSpreadsheet\Reader\Csv as CsvReader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Dompdf/PaperSizeArrayTest.php b/tests/PhpSpreadsheetTests/Writer/Dompdf/PaperSizeArrayTest.php
index 815d7e3dcc..adf2aa19a1 100644
--- a/tests/PhpSpreadsheetTests/Writer/Dompdf/PaperSizeArrayTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Dompdf/PaperSizeArrayTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Dompdf;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Dompdf/TextRotationTest.php b/tests/PhpSpreadsheetTests/Writer/Dompdf/TextRotationTest.php
index 2aa9d5ed80..7e8ee30880 100644
--- a/tests/PhpSpreadsheetTests/Writer/Dompdf/TextRotationTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Dompdf/TextRotationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Dompdf;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/AllOrOneSheetTest.php b/tests/PhpSpreadsheetTests/Writer/Html/AllOrOneSheetTest.php
index 31ed438e26..2a0cb9feb0 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/AllOrOneSheetTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/AllOrOneSheetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use DOMDocument;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/CallbackTest.php b/tests/PhpSpreadsheetTests/Writer/Html/CallbackTest.php
index 818ee9a320..2684cd559c 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/CallbackTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/CallbackTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/ExtendForChartsAndImagesTest.php b/tests/PhpSpreadsheetTests/Writer/Html/ExtendForChartsAndImagesTest.php
index e3d23230c1..3802196590 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/ExtendForChartsAndImagesTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/ExtendForChartsAndImagesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/FixHeightTest.php b/tests/PhpSpreadsheetTests/Writer/Html/FixHeightTest.php
index 745aabb698..48b9ba7d57 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/FixHeightTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/FixHeightTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/GridlinesTest.php b/tests/PhpSpreadsheetTests/Writer/Html/GridlinesTest.php
index 08af7c59f5..89455bd030 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/GridlinesTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/GridlinesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use DOMDocument;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/HtmlCommentsTest.php b/tests/PhpSpreadsheetTests/Writer/Html/HtmlCommentsTest.php
index 22b2d4c1d9..53c62ece0f 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/HtmlCommentsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/HtmlCommentsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
@@ -52,10 +54,8 @@ public static function providerCommentRichText(): array
 
     /**
      * @dataProvider providerCommentRichText
-     *
-     * @param mixed $richText
      */
-    public function testComments($richText): void
+    public function testComments(RichText $richText): void
     {
         $this->spreadsheet = new Spreadsheet();
 
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/HtmlNumberFormatTest.php b/tests/PhpSpreadsheetTests/Writer/Html/HtmlNumberFormatTest.php
index 92a904660c..1594a6fa34 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/HtmlNumberFormatTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/HtmlNumberFormatTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use DOMDocument;
@@ -11,20 +13,11 @@
 
 class HtmlNumberFormatTest extends Functional\AbstractFunctional
 {
-    /**
-     * @var string
-     */
-    private $currency;
+    private string $currency;
 
-    /**
-     * @var string
-     */
-    private $decsep;
+    private string $decsep;
 
-    /**
-     * @var string
-     */
-    private $thosep;
+    private string $thosep;
 
     protected function setUp(): void
     {
@@ -153,12 +146,8 @@ public function testColorNumberFormatComplex(): void
 
     /**
      * @dataProvider providerNumberFormat
-     *
-     * @param mixed $expectedResult
-     * @param mixed $val
-     * @param mixed $fmt
      */
-    public function testFormatValueWithMask($expectedResult, $val, $fmt): void
+    public function testFormatValueWithMask(mixed $expectedResult, mixed $val, mixed $fmt): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
@@ -189,12 +178,8 @@ public static function providerNumberFormat(): array
 
     /**
      * @dataProvider providerNumberFormatDates
-     *
-     * @param mixed $expectedResult
-     * @param mixed $val
-     * @param mixed $fmt
      */
-    public function testFormatValueWithMaskDate($expectedResult, $val, $fmt): void
+    public function testFormatValueWithMaskDate(mixed $expectedResult, mixed $val, mixed $fmt): void
     {
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/ImageCopyTest.php b/tests/PhpSpreadsheetTests/Writer/Html/ImageCopyTest.php
index adee76b08d..83e8bdf041 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/ImageCopyTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/ImageCopyTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls as XlsReader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/ImagesRootTest.php b/tests/PhpSpreadsheetTests/Writer/Html/ImagesRootTest.php
index b36a87c0b1..f36fa3b95d 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/ImagesRootTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/ImagesRootTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use DOMDocument;
@@ -9,10 +11,7 @@
 
 class ImagesRootTest extends Functional\AbstractFunctional
 {
-    /**
-     * @var string
-     */
-    private $curdir = '';
+    private string $curdir = '';
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/InvalidFileNameTest.php b/tests/PhpSpreadsheetTests/Writer/Html/InvalidFileNameTest.php
index 36a40e965b..e4621c58a3 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/InvalidFileNameTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/InvalidFileNameTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/Issue3678Test.php b/tests/PhpSpreadsheetTests/Writer/Html/Issue3678Test.php
index 5c0a7cd02b..cabcaca8ff 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/Issue3678Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/Issue3678Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/MemoryDrawingOffsetTest.php b/tests/PhpSpreadsheetTests/Writer/Html/MemoryDrawingOffsetTest.php
index e367f174df..ab2baea817 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/MemoryDrawingOffsetTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/MemoryDrawingOffsetTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/RepeatedRowsTest.php b/tests/PhpSpreadsheetTests/Writer/Html/RepeatedRowsTest.php
index 2a0f60c1a3..50d505d9a5 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/RepeatedRowsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/RepeatedRowsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use DOMDocument;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/TextRotationTest.php b/tests/PhpSpreadsheetTests/Writer/Html/TextRotationTest.php
index da92845764..2480e04b9e 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/TextRotationTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/TextRotationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/VisibilityTest.php b/tests/PhpSpreadsheetTests/Writer/Html/VisibilityTest.php
index 1c1ffb0698..75987f83a7 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/VisibilityTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/VisibilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Html/XssVulnerabilityTest.php b/tests/PhpSpreadsheetTests/Writer/Html/XssVulnerabilityTest.php
index d5396b2212..9f7d6894da 100644
--- a/tests/PhpSpreadsheetTests/Writer/Html/XssVulnerabilityTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Html/XssVulnerabilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Html;
 
 use PhpOffice\PhpSpreadsheet\IOFactory;
@@ -20,11 +22,8 @@ public static function providerAcceptableMarkupRichText(): array
 
     /**
      * @dataProvider providerAcceptableMarkupRichText
-     *
-     * @param string $safeTextString
-     * @param string $adjustedTextString
      */
-    public function testMarkupInComment($safeTextString, $adjustedTextString): void
+    public function testMarkupInComment(string $safeTextString, string $adjustedTextString): void
     {
         $spreadsheet = new Spreadsheet();
 
@@ -61,10 +60,8 @@ public static function providerXssRichText(): array
 
     /**
      * @dataProvider providerXssRichText
-     *
-     * @param string $xssTextString
      */
-    public function testXssInComment($xssTextString): void
+    public function testXssInComment(string $xssTextString): void
     {
         $spreadsheet = new Spreadsheet();
 
diff --git a/tests/PhpSpreadsheetTests/Writer/Mpdf/ImageCopyPdfTest.php b/tests/PhpSpreadsheetTests/Writer/Mpdf/ImageCopyPdfTest.php
index 5d31bc0108..c9aae25b71 100644
--- a/tests/PhpSpreadsheetTests/Writer/Mpdf/ImageCopyPdfTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Mpdf/ImageCopyPdfTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Mpdf;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xls as XlsReader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Mpdf/OrientationTest.php b/tests/PhpSpreadsheetTests/Writer/Mpdf/OrientationTest.php
index c04e8432ea..8f5fde5bc7 100644
--- a/tests/PhpSpreadsheetTests/Writer/Mpdf/OrientationTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Mpdf/OrientationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Mpdf;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Mpdf/TextRotationTest.php b/tests/PhpSpreadsheetTests/Writer/Mpdf/TextRotationTest.php
index 000a33b4b2..4f9c7557c3 100644
--- a/tests/PhpSpreadsheetTests/Writer/Mpdf/TextRotationTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Mpdf/TextRotationTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Mpdf;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Ods/AutoFilterTest.php b/tests/PhpSpreadsheetTests/Writer/Ods/AutoFilterTest.php
index 4368ef76e3..ddfe85570a 100644
--- a/tests/PhpSpreadsheetTests/Writer/Ods/AutoFilterTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Ods/AutoFilterTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Ods;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php b/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php
index 81c244a768..ae8239cca5 100644
--- a/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Ods/ContentTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Ods;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Functions;
@@ -22,14 +24,7 @@ class ContentTest extends TestCase
      */
     private $samplesPath = 'tests/data/Writer/Ods';
 
-    /**
-     * @var string
-     */
-
-    /**
-     * @var string
-     */
-    private $compatibilityMode;
+    private string $compatibilityMode;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Writer/Ods/DefinedNamesTest.php b/tests/PhpSpreadsheetTests/Writer/Ods/DefinedNamesTest.php
index 1b2e30b28a..771b90b6e9 100644
--- a/tests/PhpSpreadsheetTests/Writer/Ods/DefinedNamesTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Ods/DefinedNamesTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Ods;
 
 use PhpOffice\PhpSpreadsheet\NamedFormula;
diff --git a/tests/PhpSpreadsheetTests/Writer/Ods/MergeRangeTest.php b/tests/PhpSpreadsheetTests/Writer/Ods/MergeRangeTest.php
index 30ca697006..c029b08d05 100644
--- a/tests/PhpSpreadsheetTests/Writer/Ods/MergeRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Ods/MergeRangeTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Ods;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/PreCalcTest.php b/tests/PhpSpreadsheetTests/Writer/PreCalcTest.php
index 04cbc77f8b..8dd6ee4a3f 100644
--- a/tests/PhpSpreadsheetTests/Writer/PreCalcTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/PreCalcTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Writer/RetainSelectedCellsTest.php b/tests/PhpSpreadsheetTests/Writer/RetainSelectedCellsTest.php
index 13670b8584..70e2ccd2bd 100644
--- a/tests/PhpSpreadsheetTests/Writer/RetainSelectedCellsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/RetainSelectedCellsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/BooleanLiteralTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/BooleanLiteralTest.php
index 3528308b14..69d267f4ed 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/BooleanLiteralTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/BooleanLiteralTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/FormulaErrTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/FormulaErrTest.php
index 48cba12a64..9dc7281b69 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/FormulaErrTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/FormulaErrTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheet\NamedRange;
@@ -16,8 +18,7 @@ class FormulaErrTest extends AbstractFunctional
     /** @var ?Spreadsheet */
     private $reloadedSpreadsheet;
 
-    /** @var bool */
-    private $allowThrow;
+    private bool $allowThrow;
 
     protected function setUp(): void
     {
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/Issue642Test.php b/tests/PhpSpreadsheetTests/Writer/Xls/Issue642Test.php
index 1a86c7993c..1334249846 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/Issue642Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/Issue642Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/ParserTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/ParserTest.php
index 38fd29d336..9a283ddbee 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/ParserTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/ParserTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/Sample19Test.php b/tests/PhpSpreadsheetTests/Writer/Xls/Sample19Test.php
index 13fa9fa1df..23d3bc1135 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/Sample19Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/Sample19Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheetTests\Functional\AbstractFunctional;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/VisibilityTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/VisibilityTest.php
index 07aeaeaa5d..cd0de111db 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/VisibilityTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/VisibilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php
index ed3deb3e6a..532f22b0be 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/WorkbookTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -136,12 +138,8 @@ public function arrayAddColor(): array
 
     /**
      * Change palette color to rgb string.
-     *
-     * @param array $palette palette color
-     *
-     * @return string rgb string
      */
-    private function paletteToColor($palette)
+    private function paletteToColor(array $palette): string
     {
         return $this->right('00' . dechex((int) ($palette[0])), 2)
             . $this->right('00' . dechex((int) ($palette[1])), 2)
@@ -153,10 +151,8 @@ private function paletteToColor($palette)
      *
      * @param string $value text to get right character
      * @param int $nbchar number of char at right of string
-     *
-     * @return string
      */
-    private function right($value, $nbchar)
+    private function right(string $value, int $nbchar): string
     {
         return mb_substr($value, mb_strlen($value) - $nbchar, $nbchar);
     }
diff --git a/tests/PhpSpreadsheetTests/Writer/Xls/XlsGifBmpTest.php b/tests/PhpSpreadsheetTests/Writer/Xls/XlsGifBmpTest.php
index 412ca45be2..5f9c5d91d6 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xls/XlsGifBmpTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xls/XlsGifBmpTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xls;
 
 use DateTime;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/ArrayFormulaPrefixTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/ArrayFormulaPrefixTest.php
index 1e9505af54..e6d6e085f3 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/ArrayFormulaPrefixTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/ArrayFormulaPrefixTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/CalculationErrorTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/CalculationErrorTest.php
index d4b4e6eab6..9b61bf6360 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/CalculationErrorTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/CalculationErrorTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalFillTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalFillTest.php
index 541a6193b4..42930c1dbb 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalFillTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalFillTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalTest.php
index da2e0eecaa..bceed1050f 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/ConditionalTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsInsertRowsTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsInsertRowsTest.php
index e2cbbff37a..fcae0fd055 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsInsertRowsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsInsertRowsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsTest.php
index 26edd23d01..26c55a0560 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/DrawingsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Comment;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/FloatsRetainedTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/FloatsRetainedTest.php
index d8d2119adf..85b68cc40e 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/FloatsRetainedTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/FloatsRetainedTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as Reader;
@@ -12,10 +14,8 @@ class FloatsRetainedTest extends TestCase
 {
     /**
      * @dataProvider providerIntyFloatsRetainedByWriter
-     *
-     * @param float|int $value
      */
-    public function testIntyFloatsRetainedByWriter($value): void
+    public function testIntyFloatsRetainedByWriter(float|int $value): void
     {
         $outputFilename = File::temporaryFilename();
         $spreadsheet = new Spreadsheet();
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/FunctionPrefixTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/FunctionPrefixTest.php
index 3efeb65c78..85c0c67e60 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/FunctionPrefixTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/FunctionPrefixTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Writer\Xlsx\FunctionPrefix;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2082Test.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2082Test.php
index 1f72a3821d..11a3c6f250 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2082Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2082Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2266Test.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2266Test.php
index da6fea4e6f..637dec1d09 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2266Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2266Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as Reader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2368Test.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2368Test.php
index 8915f5df9b..6a03a9cbb9 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2368Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue2368Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataValidation;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue3443Test.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue3443Test.php
index a54cb46ce5..8b658bbf0b 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue3443Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/Issue3443Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php
index 7a4b9ca28a..185154e1bd 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/LocaleFloatsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
@@ -7,10 +9,7 @@
 
 class LocaleFloatsTest extends AbstractFunctional
 {
-    /**
-     * @var bool
-     */
-    private $localeAdjusted;
+    private bool $localeAdjusted;
 
     /**
      * @var false|string
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php
index bbc7fe230c..67380e1ba8 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/MemoryDrawingTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use GdImage;
@@ -67,10 +69,8 @@ public function testIssue3624(): void
      * Determine if image uses transparency.
      *
      * @see https://stackoverflow.com/questions/5495275/how-to-check-if-a-png-image-has-transparency-using-gd
-     *
-     * @param GdImage|resource $im
      */
-    private static function checkTransparent($im): bool
+    private static function checkTransparent(GdImage $im): bool
     {
         $width = imagesx($im); // Get the width of the image
         $height = imagesy($im); // Get the height of the image
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/StartsWithHashTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/StartsWithHashTest.php
index ebc3c92f9d..9b87c11ad3 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/StartsWithHashTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/StartsWithHashTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/TableTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/TableTest.php
index c3de920463..6636af5ddb 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/TableTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/TableTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeColorsTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeColorsTest.php
index 7eae3e5170..1b18603c5b 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeColorsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeColorsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeFontsTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeFontsTest.php
index 8c99ac9770..6e7f66f0b8 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeFontsTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/ThemeFontsTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/Unparsed2396Test.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/Unparsed2396Test.php
index 92a05efa6a..a27758b38c 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/Unparsed2396Test.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/Unparsed2396Test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as Reader;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php
index eba7288f10..94ddaf42e5 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataCloneTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Shared\File;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataTest.php
index 72d85a25b5..f31e6718c2 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/UnparsedDataTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use Exception;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/VisibilityTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/VisibilityTest.php
index 8ff6ceff4b..af3b040b1c 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/VisibilityTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/VisibilityTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
diff --git a/tests/PhpSpreadsheetTests/Writer/Xlsx/WmfTest.php b/tests/PhpSpreadsheetTests/Writer/Xlsx/WmfTest.php
index b43b135884..76dde67aae 100644
--- a/tests/PhpSpreadsheetTests/Writer/Xlsx/WmfTest.php
+++ b/tests/PhpSpreadsheetTests/Writer/Xlsx/WmfTest.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PhpOffice\PhpSpreadsheetTests\Writer\Xlsx;
 
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 6b6dc01c88..4cd23357de 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,9 +1,8 @@
 <?php
 
-setlocale(LC_ALL, 'en_US.utf8');
+declare(strict_types=1);
 
-// PHP 5.3 Compat
-//date_default_timezone_set('Europe/London');
+setlocale(LC_ALL, 'en_US.utf8');
 
 function phpunit10ErrorHandler(int $errno, string $errstr, string $filename, int $lineno): bool
 {
diff --git a/tests/data/Calculation/BinaryComparisonOperations.php b/tests/data/Calculation/BinaryComparisonOperations.php
index 8a6d79f879..bbaba28401 100644
--- a/tests/data/Calculation/BinaryComparisonOperations.php
+++ b/tests/data/Calculation/BinaryComparisonOperations.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [null, null, '=', true, true],
     [null, null, '<>', false, false],
diff --git a/tests/data/Calculation/Calculation.php b/tests/data/Calculation/Calculation.php
index e49bed9fed..27cafc90bc 100644
--- a/tests/data/Calculation/Calculation.php
+++ b/tests/data/Calculation/Calculation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 function calculationTestDataGenerator(): array
 {
     $dataArray1 = [
diff --git a/tests/data/Calculation/DateTime/DATE.php b/tests/data/Calculation/DateTime/DATE.php
index 3bed36f1cb..d585846da2 100644
--- a/tests/data/Calculation/DateTime/DATE.php
+++ b/tests/data/Calculation/DateTime/DATE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/DATEDIF.php b/tests/data/Calculation/DateTime/DATEDIF.php
index 1da3c66431..80746a7e0d 100644
--- a/tests/data/Calculation/DateTime/DATEDIF.php
+++ b/tests/data/Calculation/DateTime/DATEDIF.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/DATEVALUE.php b/tests/data/Calculation/DateTime/DATEVALUE.php
index 508a06c1e7..3f5ea10ec0 100644
--- a/tests/data/Calculation/DateTime/DATEVALUE.php
+++ b/tests/data/Calculation/DateTime/DATEVALUE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 //  Date String, Result
diff --git a/tests/data/Calculation/DateTime/DAY.php b/tests/data/Calculation/DateTime/DAY.php
index a2ccc55c3c..b23db50944 100644
--- a/tests/data/Calculation/DateTime/DAY.php
+++ b/tests/data/Calculation/DateTime/DAY.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 //  Excel Result, Argument
diff --git a/tests/data/Calculation/DateTime/DAYOpenOffice.php b/tests/data/Calculation/DateTime/DAYOpenOffice.php
index a9cef9e609..9f3799fb15 100644
--- a/tests/data/Calculation/DateTime/DAYOpenOffice.php
+++ b/tests/data/Calculation/DateTime/DAYOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 //  OpenOffice Result, Argument
diff --git a/tests/data/Calculation/DateTime/DAYS.php b/tests/data/Calculation/DateTime/DAYS.php
index 8fd2a91a57..811198c09d 100644
--- a/tests/data/Calculation/DateTime/DAYS.php
+++ b/tests/data/Calculation/DateTime/DAYS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/DAYS360.php b/tests/data/Calculation/DateTime/DAYS360.php
index 02ea5f377a..aeadaae2c7 100644
--- a/tests/data/Calculation/DateTime/DAYS360.php
+++ b/tests/data/Calculation/DateTime/DAYS360.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/EDATE.php b/tests/data/Calculation/DateTime/EDATE.php
index 197f433355..c4d284677f 100644
--- a/tests/data/Calculation/DateTime/EDATE.php
+++ b/tests/data/Calculation/DateTime/EDATE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/EOMONTH.php b/tests/data/Calculation/DateTime/EOMONTH.php
index 57edf58bc2..8143a40dfe 100644
--- a/tests/data/Calculation/DateTime/EOMONTH.php
+++ b/tests/data/Calculation/DateTime/EOMONTH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/HOUR.php b/tests/data/Calculation/DateTime/HOUR.php
index 0ed74119bd..ea4fb32670 100644
--- a/tests/data/Calculation/DateTime/HOUR.php
+++ b/tests/data/Calculation/DateTime/HOUR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/ISOWEEKNUM.php b/tests/data/Calculation/DateTime/ISOWEEKNUM.php
index 0d48ef1c22..6758f0f138 100644
--- a/tests/data/Calculation/DateTime/ISOWEEKNUM.php
+++ b/tests/data/Calculation/DateTime/ISOWEEKNUM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/ISOWEEKNUM1904.php b/tests/data/Calculation/DateTime/ISOWEEKNUM1904.php
index 6eedca42bb..649c45708e 100644
--- a/tests/data/Calculation/DateTime/ISOWEEKNUM1904.php
+++ b/tests/data/Calculation/DateTime/ISOWEEKNUM1904.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/MINUTE.php b/tests/data/Calculation/DateTime/MINUTE.php
index 1ef39982eb..cb984be9a3 100644
--- a/tests/data/Calculation/DateTime/MINUTE.php
+++ b/tests/data/Calculation/DateTime/MINUTE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/MONTH.php b/tests/data/Calculation/DateTime/MONTH.php
index 631ac791a1..4aed030fe2 100644
--- a/tests/data/Calculation/DateTime/MONTH.php
+++ b/tests/data/Calculation/DateTime/MONTH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/NETWORKDAYS.php b/tests/data/Calculation/DateTime/NETWORKDAYS.php
index cc4ef578df..f364c51933 100644
--- a/tests/data/Calculation/DateTime/NETWORKDAYS.php
+++ b/tests/data/Calculation/DateTime/NETWORKDAYS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/SECOND.php b/tests/data/Calculation/DateTime/SECOND.php
index 177c471d62..1128385204 100644
--- a/tests/data/Calculation/DateTime/SECOND.php
+++ b/tests/data/Calculation/DateTime/SECOND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/TIME.php b/tests/data/Calculation/DateTime/TIME.php
index 36460cdc3f..7d46b09fe6 100644
--- a/tests/data/Calculation/DateTime/TIME.php
+++ b/tests/data/Calculation/DateTime/TIME.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/TIMEVALUE.php b/tests/data/Calculation/DateTime/TIMEVALUE.php
index 44f4212a9b..008d923fcd 100644
--- a/tests/data/Calculation/DateTime/TIMEVALUE.php
+++ b/tests/data/Calculation/DateTime/TIMEVALUE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/WEEKDAY.php b/tests/data/Calculation/DateTime/WEEKDAY.php
index 32423f070e..bd66b8c8d8 100644
--- a/tests/data/Calculation/DateTime/WEEKDAY.php
+++ b/tests/data/Calculation/DateTime/WEEKDAY.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/WEEKNUM.php b/tests/data/Calculation/DateTime/WEEKNUM.php
index c77ff1a579..bb6ee2a2af 100644
--- a/tests/data/Calculation/DateTime/WEEKNUM.php
+++ b/tests/data/Calculation/DateTime/WEEKNUM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/WEEKNUM1904.php b/tests/data/Calculation/DateTime/WEEKNUM1904.php
index a8347f8956..a70ebe756e 100644
--- a/tests/data/Calculation/DateTime/WEEKNUM1904.php
+++ b/tests/data/Calculation/DateTime/WEEKNUM1904.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/WORKDAY.php b/tests/data/Calculation/DateTime/WORKDAY.php
index 7bb6a012ac..f1d15424e2 100644
--- a/tests/data/Calculation/DateTime/WORKDAY.php
+++ b/tests/data/Calculation/DateTime/WORKDAY.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/YEAR.php b/tests/data/Calculation/DateTime/YEAR.php
index bcb3e2bf16..d8bd371884 100644
--- a/tests/data/Calculation/DateTime/YEAR.php
+++ b/tests/data/Calculation/DateTime/YEAR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/DateTime/YEARFRAC.php b/tests/data/Calculation/DateTime/YEARFRAC.php
index 13de34b4d8..7613519c58 100644
--- a/tests/data/Calculation/DateTime/YEARFRAC.php
+++ b/tests/data/Calculation/DateTime/YEARFRAC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BESSELI.php b/tests/data/Calculation/Engineering/BESSELI.php
index c086f4fb69..f726403567 100644
--- a/tests/data/Calculation/Engineering/BESSELI.php
+++ b/tests/data/Calculation/Engineering/BESSELI.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BESSELJ.php b/tests/data/Calculation/Engineering/BESSELJ.php
index 943f91a8f7..7f0f0908b5 100644
--- a/tests/data/Calculation/Engineering/BESSELJ.php
+++ b/tests/data/Calculation/Engineering/BESSELJ.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BESSELK.php b/tests/data/Calculation/Engineering/BESSELK.php
index 431997ccfa..507f827097 100644
--- a/tests/data/Calculation/Engineering/BESSELK.php
+++ b/tests/data/Calculation/Engineering/BESSELK.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BESSELY.php b/tests/data/Calculation/Engineering/BESSELY.php
index fa2ca3cd3b..006e74c669 100644
--- a/tests/data/Calculation/Engineering/BESSELY.php
+++ b/tests/data/Calculation/Engineering/BESSELY.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BIN2DEC.php b/tests/data/Calculation/Engineering/BIN2DEC.php
index d510d0bbcf..48fa613e6c 100644
--- a/tests/data/Calculation/Engineering/BIN2DEC.php
+++ b/tests/data/Calculation/Engineering/BIN2DEC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BIN2DECOpenOffice.php b/tests/data/Calculation/Engineering/BIN2DECOpenOffice.php
index 54fe1700a3..1b26a8f04c 100644
--- a/tests/data/Calculation/Engineering/BIN2DECOpenOffice.php
+++ b/tests/data/Calculation/Engineering/BIN2DECOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // Boolean okay for ODS, not for Excel/Gnumeric
     ['0', false], // Boolean okay for ODS, not for Excel/Gnumeric
diff --git a/tests/data/Calculation/Engineering/BIN2HEX.php b/tests/data/Calculation/Engineering/BIN2HEX.php
index ffb89706c2..1cd240cdff 100644
--- a/tests/data/Calculation/Engineering/BIN2HEX.php
+++ b/tests/data/Calculation/Engineering/BIN2HEX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BIN2HEXOpenOffice.php b/tests/data/Calculation/Engineering/BIN2HEXOpenOffice.php
index 54fe1700a3..1b26a8f04c 100644
--- a/tests/data/Calculation/Engineering/BIN2HEXOpenOffice.php
+++ b/tests/data/Calculation/Engineering/BIN2HEXOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // Boolean okay for ODS, not for Excel/Gnumeric
     ['0', false], // Boolean okay for ODS, not for Excel/Gnumeric
diff --git a/tests/data/Calculation/Engineering/BIN2OCT.php b/tests/data/Calculation/Engineering/BIN2OCT.php
index bd656192d8..55cddb61c2 100644
--- a/tests/data/Calculation/Engineering/BIN2OCT.php
+++ b/tests/data/Calculation/Engineering/BIN2OCT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BIN2OCTOpenOffice.php b/tests/data/Calculation/Engineering/BIN2OCTOpenOffice.php
index 54fe1700a3..1b26a8f04c 100644
--- a/tests/data/Calculation/Engineering/BIN2OCTOpenOffice.php
+++ b/tests/data/Calculation/Engineering/BIN2OCTOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // Boolean okay for ODS, not for Excel/Gnumeric
     ['0', false], // Boolean okay for ODS, not for Excel/Gnumeric
diff --git a/tests/data/Calculation/Engineering/BITAND.php b/tests/data/Calculation/Engineering/BITAND.php
index 4cfe42c06b..a6608459de 100644
--- a/tests/data/Calculation/Engineering/BITAND.php
+++ b/tests/data/Calculation/Engineering/BITAND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BITLSHIFT.php b/tests/data/Calculation/Engineering/BITLSHIFT.php
index c63572408d..b6059cd281 100644
--- a/tests/data/Calculation/Engineering/BITLSHIFT.php
+++ b/tests/data/Calculation/Engineering/BITLSHIFT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BITOR.php b/tests/data/Calculation/Engineering/BITOR.php
index 8f1c2290a4..745c98224f 100644
--- a/tests/data/Calculation/Engineering/BITOR.php
+++ b/tests/data/Calculation/Engineering/BITOR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BITRSHIFT.php b/tests/data/Calculation/Engineering/BITRSHIFT.php
index 08e46ea6b8..9ddc2e83e0 100644
--- a/tests/data/Calculation/Engineering/BITRSHIFT.php
+++ b/tests/data/Calculation/Engineering/BITRSHIFT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/BITXOR.php b/tests/data/Calculation/Engineering/BITXOR.php
index 2a538f155a..ec886a6bd1 100644
--- a/tests/data/Calculation/Engineering/BITXOR.php
+++ b/tests/data/Calculation/Engineering/BITXOR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/COMPLEX.php b/tests/data/Calculation/Engineering/COMPLEX.php
index 0979caa660..56f5f61df9 100644
--- a/tests/data/Calculation/Engineering/COMPLEX.php
+++ b/tests/data/Calculation/Engineering/COMPLEX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/CONVERTUOM.php b/tests/data/Calculation/Engineering/CONVERTUOM.php
index c6f90c82a3..7e74a4b980 100644
--- a/tests/data/Calculation/Engineering/CONVERTUOM.php
+++ b/tests/data/Calculation/Engineering/CONVERTUOM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/DEC2BIN.php b/tests/data/Calculation/Engineering/DEC2BIN.php
index 7d7bd0cfae..c3346af70a 100644
--- a/tests/data/Calculation/Engineering/DEC2BIN.php
+++ b/tests/data/Calculation/Engineering/DEC2BIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/DEC2BINOpenOffice.php b/tests/data/Calculation/Engineering/DEC2BINOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/DEC2BINOpenOffice.php
+++ b/tests/data/Calculation/Engineering/DEC2BINOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Engineering/DEC2HEX.php b/tests/data/Calculation/Engineering/DEC2HEX.php
index 49a6683f62..2b9c708cca 100644
--- a/tests/data/Calculation/Engineering/DEC2HEX.php
+++ b/tests/data/Calculation/Engineering/DEC2HEX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/DEC2HEXOpenOffice.php b/tests/data/Calculation/Engineering/DEC2HEXOpenOffice.php
index b0972e3ce6..bd2b7fe826 100644
--- a/tests/data/Calculation/Engineering/DEC2HEXOpenOffice.php
+++ b/tests/data/Calculation/Engineering/DEC2HEXOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts bool, Excel/Gnumeric do not
     ['0', false],
diff --git a/tests/data/Calculation/Engineering/DEC2OCT.php b/tests/data/Calculation/Engineering/DEC2OCT.php
index 400ffdec51..72cd06a900 100644
--- a/tests/data/Calculation/Engineering/DEC2OCT.php
+++ b/tests/data/Calculation/Engineering/DEC2OCT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/DEC2OCTOpenOffice.php b/tests/data/Calculation/Engineering/DEC2OCTOpenOffice.php
index b0972e3ce6..bd2b7fe826 100644
--- a/tests/data/Calculation/Engineering/DEC2OCTOpenOffice.php
+++ b/tests/data/Calculation/Engineering/DEC2OCTOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts bool, Excel/Gnumeric do not
     ['0', false],
diff --git a/tests/data/Calculation/Engineering/DELTA.php b/tests/data/Calculation/Engineering/DELTA.php
index d2e605b9f4..df72447b83 100644
--- a/tests/data/Calculation/Engineering/DELTA.php
+++ b/tests/data/Calculation/Engineering/DELTA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/ERF.php b/tests/data/Calculation/Engineering/ERF.php
index 68fd0e4b5f..5f7c821806 100644
--- a/tests/data/Calculation/Engineering/ERF.php
+++ b/tests/data/Calculation/Engineering/ERF.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 //  Result, lower bound, upper bound,
diff --git a/tests/data/Calculation/Engineering/ERFC.php b/tests/data/Calculation/Engineering/ERFC.php
index 5bc85cf7d2..259d493e6d 100644
--- a/tests/data/Calculation/Engineering/ERFC.php
+++ b/tests/data/Calculation/Engineering/ERFC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 //  Result, x value
diff --git a/tests/data/Calculation/Engineering/ERFPRECISE.php b/tests/data/Calculation/Engineering/ERFPRECISE.php
index 0cc53abbc1..ba902b9706 100644
--- a/tests/data/Calculation/Engineering/ERFPRECISE.php
+++ b/tests/data/Calculation/Engineering/ERFPRECISE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 //  Result, lower bound, upper bound
 return [
     [0.0, 0],
diff --git a/tests/data/Calculation/Engineering/GESTEP.php b/tests/data/Calculation/Engineering/GESTEP.php
index 3d462df88f..8ac1a467f3 100644
--- a/tests/data/Calculation/Engineering/GESTEP.php
+++ b/tests/data/Calculation/Engineering/GESTEP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/HEX2BIN.php b/tests/data/Calculation/Engineering/HEX2BIN.php
index 130cad285c..81f3a64283 100644
--- a/tests/data/Calculation/Engineering/HEX2BIN.php
+++ b/tests/data/Calculation/Engineering/HEX2BIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/HEX2BINOpenOffice.php b/tests/data/Calculation/Engineering/HEX2BINOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/HEX2BINOpenOffice.php
+++ b/tests/data/Calculation/Engineering/HEX2BINOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Engineering/HEX2DEC.php b/tests/data/Calculation/Engineering/HEX2DEC.php
index 965ac6d211..54c95ade95 100644
--- a/tests/data/Calculation/Engineering/HEX2DEC.php
+++ b/tests/data/Calculation/Engineering/HEX2DEC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/HEX2DECOpenOffice.php b/tests/data/Calculation/Engineering/HEX2DECOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/HEX2DECOpenOffice.php
+++ b/tests/data/Calculation/Engineering/HEX2DECOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Engineering/HEX2OCT.php b/tests/data/Calculation/Engineering/HEX2OCT.php
index 56047372fa..713011b245 100644
--- a/tests/data/Calculation/Engineering/HEX2OCT.php
+++ b/tests/data/Calculation/Engineering/HEX2OCT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/HEX2OCTOpenOffice.php b/tests/data/Calculation/Engineering/HEX2OCTOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/HEX2OCTOpenOffice.php
+++ b/tests/data/Calculation/Engineering/HEX2OCTOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Engineering/IMABS.php b/tests/data/Calculation/Engineering/IMABS.php
index 8e3a752aa5..cb500608cc 100644
--- a/tests/data/Calculation/Engineering/IMABS.php
+++ b/tests/data/Calculation/Engineering/IMABS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMAGINARY.php b/tests/data/Calculation/Engineering/IMAGINARY.php
index 1496291646..e2ed7042dd 100644
--- a/tests/data/Calculation/Engineering/IMAGINARY.php
+++ b/tests/data/Calculation/Engineering/IMAGINARY.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMARGUMENT.php b/tests/data/Calculation/Engineering/IMARGUMENT.php
index 6c8dc928e1..65a0aa3b2b 100644
--- a/tests/data/Calculation/Engineering/IMARGUMENT.php
+++ b/tests/data/Calculation/Engineering/IMARGUMENT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMCONJUGATE.php b/tests/data/Calculation/Engineering/IMCONJUGATE.php
index ff9ae34185..ad5ba26528 100644
--- a/tests/data/Calculation/Engineering/IMCONJUGATE.php
+++ b/tests/data/Calculation/Engineering/IMCONJUGATE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMCOS.php b/tests/data/Calculation/Engineering/IMCOS.php
index 409b614ecc..7a7f64c935 100644
--- a/tests/data/Calculation/Engineering/IMCOS.php
+++ b/tests/data/Calculation/Engineering/IMCOS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMCOSH.php b/tests/data/Calculation/Engineering/IMCOSH.php
index b7458535e5..308b487980 100644
--- a/tests/data/Calculation/Engineering/IMCOSH.php
+++ b/tests/data/Calculation/Engineering/IMCOSH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMCOT.php b/tests/data/Calculation/Engineering/IMCOT.php
index 28dded62c3..48055b1c09 100644
--- a/tests/data/Calculation/Engineering/IMCOT.php
+++ b/tests/data/Calculation/Engineering/IMCOT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMCSC.php b/tests/data/Calculation/Engineering/IMCSC.php
index 9999c7bd2d..2ead169d69 100644
--- a/tests/data/Calculation/Engineering/IMCSC.php
+++ b/tests/data/Calculation/Engineering/IMCSC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMCSCH.php b/tests/data/Calculation/Engineering/IMCSCH.php
index a293f49e65..7727aac0e4 100644
--- a/tests/data/Calculation/Engineering/IMCSCH.php
+++ b/tests/data/Calculation/Engineering/IMCSCH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMDIV.php b/tests/data/Calculation/Engineering/IMDIV.php
index 4c4b371914..179265eef5 100644
--- a/tests/data/Calculation/Engineering/IMDIV.php
+++ b/tests/data/Calculation/Engineering/IMDIV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMEXP.php b/tests/data/Calculation/Engineering/IMEXP.php
index 8a00dc6781..e360745e2d 100644
--- a/tests/data/Calculation/Engineering/IMEXP.php
+++ b/tests/data/Calculation/Engineering/IMEXP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMLN.php b/tests/data/Calculation/Engineering/IMLN.php
index a74aed375d..9f39964bec 100644
--- a/tests/data/Calculation/Engineering/IMLN.php
+++ b/tests/data/Calculation/Engineering/IMLN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMLOG10.php b/tests/data/Calculation/Engineering/IMLOG10.php
index ac9957f94f..7b6b4a2bf6 100644
--- a/tests/data/Calculation/Engineering/IMLOG10.php
+++ b/tests/data/Calculation/Engineering/IMLOG10.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMLOG2.php b/tests/data/Calculation/Engineering/IMLOG2.php
index 5dd729e075..a68d04df20 100644
--- a/tests/data/Calculation/Engineering/IMLOG2.php
+++ b/tests/data/Calculation/Engineering/IMLOG2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMPOWER.php b/tests/data/Calculation/Engineering/IMPOWER.php
index 5a8bdf4e5a..04296ca07e 100644
--- a/tests/data/Calculation/Engineering/IMPOWER.php
+++ b/tests/data/Calculation/Engineering/IMPOWER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMPRODUCT.php b/tests/data/Calculation/Engineering/IMPRODUCT.php
index 9987ba69da..db60961db6 100644
--- a/tests/data/Calculation/Engineering/IMPRODUCT.php
+++ b/tests/data/Calculation/Engineering/IMPRODUCT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMREAL.php b/tests/data/Calculation/Engineering/IMREAL.php
index 2586f864ee..65537d4bbd 100644
--- a/tests/data/Calculation/Engineering/IMREAL.php
+++ b/tests/data/Calculation/Engineering/IMREAL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSEC.php b/tests/data/Calculation/Engineering/IMSEC.php
index 5e9e51284b..2b7cc3cb4b 100644
--- a/tests/data/Calculation/Engineering/IMSEC.php
+++ b/tests/data/Calculation/Engineering/IMSEC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSECH.php b/tests/data/Calculation/Engineering/IMSECH.php
index e7fd30cfc0..13aa4f805c 100644
--- a/tests/data/Calculation/Engineering/IMSECH.php
+++ b/tests/data/Calculation/Engineering/IMSECH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSIN.php b/tests/data/Calculation/Engineering/IMSIN.php
index b68b2e7163..c45fd94132 100644
--- a/tests/data/Calculation/Engineering/IMSIN.php
+++ b/tests/data/Calculation/Engineering/IMSIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSINH.php b/tests/data/Calculation/Engineering/IMSINH.php
index 4545d5013f..31ff846949 100644
--- a/tests/data/Calculation/Engineering/IMSINH.php
+++ b/tests/data/Calculation/Engineering/IMSINH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSQRT.php b/tests/data/Calculation/Engineering/IMSQRT.php
index 0b0259f3b4..8a5cc1aa65 100644
--- a/tests/data/Calculation/Engineering/IMSQRT.php
+++ b/tests/data/Calculation/Engineering/IMSQRT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSUB.php b/tests/data/Calculation/Engineering/IMSUB.php
index 068558760e..90f4c7462c 100644
--- a/tests/data/Calculation/Engineering/IMSUB.php
+++ b/tests/data/Calculation/Engineering/IMSUB.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMSUM.php b/tests/data/Calculation/Engineering/IMSUM.php
index 25f877bdcb..6b2dfa2033 100644
--- a/tests/data/Calculation/Engineering/IMSUM.php
+++ b/tests/data/Calculation/Engineering/IMSUM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/IMTAN.php b/tests/data/Calculation/Engineering/IMTAN.php
index 46fa35c9a2..5b4d021b66 100644
--- a/tests/data/Calculation/Engineering/IMTAN.php
+++ b/tests/data/Calculation/Engineering/IMTAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/OCT2BIN.php b/tests/data/Calculation/Engineering/OCT2BIN.php
index 2ab74e71ae..79da0e0efa 100644
--- a/tests/data/Calculation/Engineering/OCT2BIN.php
+++ b/tests/data/Calculation/Engineering/OCT2BIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/OCT2BINOpenOffice.php b/tests/data/Calculation/Engineering/OCT2BINOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/OCT2BINOpenOffice.php
+++ b/tests/data/Calculation/Engineering/OCT2BINOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Engineering/OCT2DEC.php b/tests/data/Calculation/Engineering/OCT2DEC.php
index caea03986c..fb88a71f54 100644
--- a/tests/data/Calculation/Engineering/OCT2DEC.php
+++ b/tests/data/Calculation/Engineering/OCT2DEC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/OCT2DECOpenOffice.php b/tests/data/Calculation/Engineering/OCT2DECOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/OCT2DECOpenOffice.php
+++ b/tests/data/Calculation/Engineering/OCT2DECOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Engineering/OCT2HEX.php b/tests/data/Calculation/Engineering/OCT2HEX.php
index a6b5536f53..a8897989a0 100644
--- a/tests/data/Calculation/Engineering/OCT2HEX.php
+++ b/tests/data/Calculation/Engineering/OCT2HEX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Engineering/OCT2HEXOpenOffice.php b/tests/data/Calculation/Engineering/OCT2HEXOpenOffice.php
index 31adb5f274..f0e2686358 100644
--- a/tests/data/Calculation/Engineering/OCT2HEXOpenOffice.php
+++ b/tests/data/Calculation/Engineering/OCT2HEXOpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['1', true], // ODS accepts boolean, Excel/Gnumeric don't
     ['0', false], // ODS accepts boolean, Excel/Gnumeric don't
diff --git a/tests/data/Calculation/Financial/ACCRINT.php b/tests/data/Calculation/Financial/ACCRINT.php
index a7b508d16a..d707b36eee 100644
--- a/tests/data/Calculation/Financial/ACCRINT.php
+++ b/tests/data/Calculation/Financial/ACCRINT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Issue date, 1st Interest, Settlement, Rate, Par, Freq, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/ACCRINTM.php b/tests/data/Calculation/Financial/ACCRINTM.php
index 444e41f90b..8a9e1b1222 100644
--- a/tests/data/Calculation/Financial/ACCRINTM.php
+++ b/tests/data/Calculation/Financial/ACCRINTM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Issue date, Settlement, Rate, Par, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/AMORDEGRC.php b/tests/data/Calculation/Financial/AMORDEGRC.php
index fa546c8cd4..caaa29cc4c 100644
--- a/tests/data/Calculation/Financial/AMORDEGRC.php
+++ b/tests/data/Calculation/Financial/AMORDEGRC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Cost, Date purchased, End of the 1st period, Salvage, Period, Depreciation, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/AMORLINC.php b/tests/data/Calculation/Financial/AMORLINC.php
index c017553684..d27c1b83de 100644
--- a/tests/data/Calculation/Financial/AMORLINC.php
+++ b/tests/data/Calculation/Financial/AMORLINC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Cost, Date purchased, End of the 1st period, Salvage, Period, Depreciation, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/COUPDAYBS.php b/tests/data/Calculation/Financial/COUPDAYBS.php
index f41d3620c0..8f8c873c52 100644
--- a/tests/data/Calculation/Financial/COUPDAYBS.php
+++ b/tests/data/Calculation/Financial/COUPDAYBS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Frequency, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/COUPDAYS.php b/tests/data/Calculation/Financial/COUPDAYS.php
index caba56e55a..50834c4289 100644
--- a/tests/data/Calculation/Financial/COUPDAYS.php
+++ b/tests/data/Calculation/Financial/COUPDAYS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Frequency, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/COUPDAYSNC.php b/tests/data/Calculation/Financial/COUPDAYSNC.php
index e8500263c9..e3de4a6a00 100644
--- a/tests/data/Calculation/Financial/COUPDAYSNC.php
+++ b/tests/data/Calculation/Financial/COUPDAYSNC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Frequency, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/COUPNCD.php b/tests/data/Calculation/Financial/COUPNCD.php
index d690525c9b..e913ced01c 100644
--- a/tests/data/Calculation/Financial/COUPNCD.php
+++ b/tests/data/Calculation/Financial/COUPNCD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Frequency, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/COUPNUM.php b/tests/data/Calculation/Financial/COUPNUM.php
index 4cf0cc29b1..f46c7c2d7d 100644
--- a/tests/data/Calculation/Financial/COUPNUM.php
+++ b/tests/data/Calculation/Financial/COUPNUM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Frequency, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/COUPPCD.php b/tests/data/Calculation/Financial/COUPPCD.php
index 88b93af5c6..35ec8484ce 100644
--- a/tests/data/Calculation/Financial/COUPPCD.php
+++ b/tests/data/Calculation/Financial/COUPPCD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Frequency, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/CUMIPMT.php b/tests/data/Calculation/Financial/CUMIPMT.php
index 2ccc5ff245..2e5deeab70 100644
--- a/tests/data/Calculation/Financial/CUMIPMT.php
+++ b/tests/data/Calculation/Financial/CUMIPMT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, nper, pv, start_period, end_period, type, result
 
 return [
diff --git a/tests/data/Calculation/Financial/CUMPRINC.php b/tests/data/Calculation/Financial/CUMPRINC.php
index e14d5adc16..684e65f459 100644
--- a/tests/data/Calculation/Financial/CUMPRINC.php
+++ b/tests/data/Calculation/Financial/CUMPRINC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, nper, pv, start_period, end_period, type, result
 
 return [
diff --git a/tests/data/Calculation/Financial/DB.php b/tests/data/Calculation/Financial/DB.php
index 89bd22f2ca..6e7ca02bfe 100644
--- a/tests/data/Calculation/Financial/DB.php
+++ b/tests/data/Calculation/Financial/DB.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // cost, salvage, life, period, month, result
 
 return [
diff --git a/tests/data/Calculation/Financial/DDB.php b/tests/data/Calculation/Financial/DDB.php
index 67962ea2eb..7c6eb35d9c 100644
--- a/tests/data/Calculation/Financial/DDB.php
+++ b/tests/data/Calculation/Financial/DDB.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // cost, salvage, life, period, month, result
 
 return [
diff --git a/tests/data/Calculation/Financial/DISC.php b/tests/data/Calculation/Financial/DISC.php
index f33ed21bf1..f301081d56 100644
--- a/tests/data/Calculation/Financial/DISC.php
+++ b/tests/data/Calculation/Financial/DISC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // settlement, maturity, price, redemption, basis, result
 
 return [
diff --git a/tests/data/Calculation/Financial/DOLLARDE.php b/tests/data/Calculation/Financial/DOLLARDE.php
index 7f4c419521..0c9d82eecb 100644
--- a/tests/data/Calculation/Financial/DOLLARDE.php
+++ b/tests/data/Calculation/Financial/DOLLARDE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // fractional_dollar, fraction, result
 
 return [
diff --git a/tests/data/Calculation/Financial/DOLLARFR.php b/tests/data/Calculation/Financial/DOLLARFR.php
index 42ae133ecf..e4b49ad499 100644
--- a/tests/data/Calculation/Financial/DOLLARFR.php
+++ b/tests/data/Calculation/Financial/DOLLARFR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // decimal_dollar, fraction, result
 
 return [
diff --git a/tests/data/Calculation/Financial/DaysPerYear.php b/tests/data/Calculation/Financial/DaysPerYear.php
index 2eb51a034d..f49962cd9d 100644
--- a/tests/data/Calculation/Financial/DaysPerYear.php
+++ b/tests/data/Calculation/Financial/DaysPerYear.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Financial\Constants as FinancialConstants;
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
diff --git a/tests/data/Calculation/Financial/EFFECT.php b/tests/data/Calculation/Financial/EFFECT.php
index c81ca7f03a..cd3a336381 100644
--- a/tests/data/Calculation/Financial/EFFECT.php
+++ b/tests/data/Calculation/Financial/EFFECT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // nominal_rate, npery, Result
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/data/Calculation/Financial/FV.php b/tests/data/Calculation/Financial/FV.php
index 4dce5373ff..c7066df2e8 100644
--- a/tests/data/Calculation/Financial/FV.php
+++ b/tests/data/Calculation/Financial/FV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, nper, pmt, pv, type, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/FVSCHEDULE.php b/tests/data/Calculation/Financial/FVSCHEDULE.php
index fde67411a5..c2420b5dfb 100644
--- a/tests/data/Calculation/Financial/FVSCHEDULE.php
+++ b/tests/data/Calculation/Financial/FVSCHEDULE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // principal, schedule, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/INTRATE.php b/tests/data/Calculation/Financial/INTRATE.php
index 05e73c59f2..7162e2f017 100644
--- a/tests/data/Calculation/Financial/INTRATE.php
+++ b/tests/data/Calculation/Financial/INTRATE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Settlement, Maturity, Investment, Redemption, Basis, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/IPMT.php b/tests/data/Calculation/Financial/IPMT.php
index c8f66dea3b..5d16c07fa1 100644
--- a/tests/data/Calculation/Financial/IPMT.php
+++ b/tests/data/Calculation/Financial/IPMT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, per, nper, pv, fv, type, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/IRR.php b/tests/data/Calculation/Financial/IRR.php
index 5051182a5c..7177995c19 100644
--- a/tests/data/Calculation/Financial/IRR.php
+++ b/tests/data/Calculation/Financial/IRR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // values, guess, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/ISPMT.php b/tests/data/Calculation/Financial/ISPMT.php
index 7209f19553..e2af00fde7 100644
--- a/tests/data/Calculation/Financial/ISPMT.php
+++ b/tests/data/Calculation/Financial/ISPMT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, per, nper, pv, result
 
 return [
diff --git a/tests/data/Calculation/Financial/MIRR.php b/tests/data/Calculation/Financial/MIRR.php
index 460eb20727..d760982fd6 100644
--- a/tests/data/Calculation/Financial/MIRR.php
+++ b/tests/data/Calculation/Financial/MIRR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // values, finance_rate, reinvestment_rate, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/NOMINAL.php b/tests/data/Calculation/Financial/NOMINAL.php
index aade7da097..d81147462a 100644
--- a/tests/data/Calculation/Financial/NOMINAL.php
+++ b/tests/data/Calculation/Financial/NOMINAL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // effect_rate, npery, result
 
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
diff --git a/tests/data/Calculation/Financial/NPER.php b/tests/data/Calculation/Financial/NPER.php
index db53c501bd..92030e667a 100644
--- a/tests/data/Calculation/Financial/NPER.php
+++ b/tests/data/Calculation/Financial/NPER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, pmt, pv, fv, type, result
 
 return [
diff --git a/tests/data/Calculation/Financial/NPV.php b/tests/data/Calculation/Financial/NPV.php
index ac854269a5..8977ef1db8 100644
--- a/tests/data/Calculation/Financial/NPV.php
+++ b/tests/data/Calculation/Financial/NPV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // rate, values, result
 
 return [
diff --git a/tests/data/Calculation/Financial/PDURATION.php b/tests/data/Calculation/Financial/PDURATION.php
index e2ae671911..2a166062fa 100644
--- a/tests/data/Calculation/Financial/PDURATION.php
+++ b/tests/data/Calculation/Financial/PDURATION.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         10.33803507,
diff --git a/tests/data/Calculation/Financial/PMT.php b/tests/data/Calculation/Financial/PMT.php
index ed1907deb4..b805323c16 100644
--- a/tests/data/Calculation/Financial/PMT.php
+++ b/tests/data/Calculation/Financial/PMT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         -1037.032089359164,
diff --git a/tests/data/Calculation/Financial/PPMT.php b/tests/data/Calculation/Financial/PPMT.php
index 136e54791b..972e056e21 100644
--- a/tests/data/Calculation/Financial/PPMT.php
+++ b/tests/data/Calculation/Financial/PPMT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         -75.623186008367,
diff --git a/tests/data/Calculation/Financial/PRICE.php b/tests/data/Calculation/Financial/PRICE.php
index f1f5c50771..4e9ad13070 100644
--- a/tests/data/Calculation/Financial/PRICE.php
+++ b/tests/data/Calculation/Financial/PRICE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Result, Settlement, Maturity, Rate, Yield, Redemption, Frequency, Basis
 
 return [
diff --git a/tests/data/Calculation/Financial/PRICE3.php b/tests/data/Calculation/Financial/PRICE3.php
index c5a5c07f15..90327ac5cc 100644
--- a/tests/data/Calculation/Financial/PRICE3.php
+++ b/tests/data/Calculation/Financial/PRICE3.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Result, Settlement, Maturity, Rate, Yield, Redemption, Frequency, Basis
 // On the result line, the value is ODS's calculation.
 //     This agrees with Gnumeric, PhpSpreadsheet, and the published algorithm at:
diff --git a/tests/data/Calculation/Financial/PRICEDISC.php b/tests/data/Calculation/Financial/PRICEDISC.php
index bd3021a168..a71bfc3db4 100644
--- a/tests/data/Calculation/Financial/PRICEDISC.php
+++ b/tests/data/Calculation/Financial/PRICEDISC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         90.0,
diff --git a/tests/data/Calculation/Financial/PRICEMAT.php b/tests/data/Calculation/Financial/PRICEMAT.php
index 433b523e2d..93aab92a1b 100644
--- a/tests/data/Calculation/Financial/PRICEMAT.php
+++ b/tests/data/Calculation/Financial/PRICEMAT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         99.98449887555694,
diff --git a/tests/data/Calculation/Financial/PV.php b/tests/data/Calculation/Financial/PV.php
index b0abf57a57..81ff88aa9a 100644
--- a/tests/data/Calculation/Financial/PV.php
+++ b/tests/data/Calculation/Financial/PV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         -52990.70632392715,
diff --git a/tests/data/Calculation/Financial/RATE.php b/tests/data/Calculation/Financial/RATE.php
index f2026967ba..f5a5ab4920 100644
--- a/tests/data/Calculation/Financial/RATE.php
+++ b/tests/data/Calculation/Financial/RATE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Periods, Payment, Present Value, Future Value, Type, Guess, Result
 
 return [
diff --git a/tests/data/Calculation/Financial/RECEIVED.php b/tests/data/Calculation/Financial/RECEIVED.php
index af183ba948..e16c06f1e6 100644
--- a/tests/data/Calculation/Financial/RECEIVED.php
+++ b/tests/data/Calculation/Financial/RECEIVED.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1014584.6544071021,
diff --git a/tests/data/Calculation/Financial/RRI.php b/tests/data/Calculation/Financial/RRI.php
index d71211b5d5..0318f45c72 100644
--- a/tests/data/Calculation/Financial/RRI.php
+++ b/tests/data/Calculation/Financial/RRI.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.04137974399241062,
diff --git a/tests/data/Calculation/Financial/SLN.php b/tests/data/Calculation/Financial/SLN.php
index f63120c19a..766d64c72d 100644
--- a/tests/data/Calculation/Financial/SLN.php
+++ b/tests/data/Calculation/Financial/SLN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1800,
diff --git a/tests/data/Calculation/Financial/SYD.php b/tests/data/Calculation/Financial/SYD.php
index a8dd078cb5..9a0056e7f8 100644
--- a/tests/data/Calculation/Financial/SYD.php
+++ b/tests/data/Calculation/Financial/SYD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3000,
diff --git a/tests/data/Calculation/Financial/TBILLEQ.php b/tests/data/Calculation/Financial/TBILLEQ.php
index 3624d171a5..bacd1fa156 100644
--- a/tests/data/Calculation/Financial/TBILLEQ.php
+++ b/tests/data/Calculation/Financial/TBILLEQ.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Financial/TBILLPRICE.php b/tests/data/Calculation/Financial/TBILLPRICE.php
index 8a1bb85a49..720c0bfad5 100644
--- a/tests/data/Calculation/Financial/TBILLPRICE.php
+++ b/tests/data/Calculation/Financial/TBILLPRICE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Financial/TBILLYIELD.php b/tests/data/Calculation/Financial/TBILLYIELD.php
index 30b417daf0..244a7481c0 100644
--- a/tests/data/Calculation/Financial/TBILLYIELD.php
+++ b/tests/data/Calculation/Financial/TBILLYIELD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Financial/USDOLLAR.php b/tests/data/Calculation/Financial/USDOLLAR.php
index 25cb4eae7c..f5fbc16183 100644
--- a/tests/data/Calculation/Financial/USDOLLAR.php
+++ b/tests/data/Calculation/Financial/USDOLLAR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['$12,345.67890', 12345.6789, 5],
 ];
diff --git a/tests/data/Calculation/Financial/XIRR.php b/tests/data/Calculation/Financial/XIRR.php
index 03bf6fee5c..f22104c15e 100644
--- a/tests/data/Calculation/Financial/XIRR.php
+++ b/tests/data/Calculation/Financial/XIRR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // result, message, values, dates, guess
 
 return [
diff --git a/tests/data/Calculation/Financial/XNPV.php b/tests/data/Calculation/Financial/XNPV.php
index 66e4d43e00..422e855dd8 100644
--- a/tests/data/Calculation/Financial/XNPV.php
+++ b/tests/data/Calculation/Financial/XNPV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // result, message, rate, values, dates
 
 return [
diff --git a/tests/data/Calculation/Financial/YIELDDISC.php b/tests/data/Calculation/Financial/YIELDDISC.php
index d9ab1957a7..b09f0c9fc8 100644
--- a/tests/data/Calculation/Financial/YIELDDISC.php
+++ b/tests/data/Calculation/Financial/YIELDDISC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.05282257198685834,
diff --git a/tests/data/Calculation/Financial/YIELDMAT.php b/tests/data/Calculation/Financial/YIELDMAT.php
index 9980f4657f..18eb9092e0 100644
--- a/tests/data/Calculation/Financial/YIELDMAT.php
+++ b/tests/data/Calculation/Financial/YIELDMAT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.06095433369153867,
diff --git a/tests/data/Calculation/Functions/IF_CONDITION.php b/tests/data/Calculation/Functions/IF_CONDITION.php
index fce8c6410b..b555f7ee02 100644
--- a/tests/data/Calculation/Functions/IF_CONDITION.php
+++ b/tests/data/Calculation/Functions/IF_CONDITION.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '<"A"',
diff --git a/tests/data/Calculation/FunctionsAsString.php b/tests/data/Calculation/FunctionsAsString.php
index 8595347239..57606c1a10 100644
--- a/tests/data/Calculation/FunctionsAsString.php
+++ b/tests/data/Calculation/FunctionsAsString.php
@@ -1,24 +1,26 @@
 <?php
 
-    return [
-        // Note that these are meant to test the parser, not a comprehensive
-        // test of all Excel functions, which tests are handled elsewhere.
-        [6, '=SUM(1,2,3)'],
-        [60, '=SUM(A1:A3)'],
-        [70, '=SUM(A1,A2,A4)'],
-        [41, '=SUM(1,namedCell)'],
-        [50, '=A1+namedCell'],
-        [3, '=MATCH(6,{4,5,6,2},0)'],
-        ['#N/A', '=MATCH(8,{4,5,6,2},0)'],
-        [7, '=HLOOKUP(5,{1,5,10;2,6,11;3,7,12;4,8,13},3,FALSE)'],
-        ['Hello, World.', '=CONCATENATE("Hello, ", "World.")'],
-        ['{NON-EMPTY SET}', '=UPPER("{non-EMPTY set}")'], // braces not used for matrix
-        ['upper', '=LOWER(B1)'],
-        [false, '=and(B2,B3)'],
-        [0, '=acos(1)'],
-        [0.785398, '=round(atan({1,2,3}),6)'], // {1,2,3} will be flattened to 1
-        [2, '=minverse({-2.5,1.5;2,-1})'], // 2 is the flattened result of {2,3;4,5}
-        [4, '=MDETERM(MMULT({1,2;3,4},{5,6;7,8}))'], // multiple matrices
-        [110, '=SUM(A1,Sheet2!$A$1)'], // different sheet absolute address
-        [220, '=SUM(A2,A2B)'], // defined name on different sheet
-    ];
+declare(strict_types=1);
+
+return [
+    // Note that these are meant to test the parser, not a comprehensive
+    // test of all Excel functions, which tests are handled elsewhere.
+    [6, '=SUM(1,2,3)'],
+    [60, '=SUM(A1:A3)'],
+    [70, '=SUM(A1,A2,A4)'],
+    [41, '=SUM(1,namedCell)'],
+    [50, '=A1+namedCell'],
+    [3, '=MATCH(6,{4,5,6,2},0)'],
+    ['#N/A', '=MATCH(8,{4,5,6,2},0)'],
+    [7, '=HLOOKUP(5,{1,5,10;2,6,11;3,7,12;4,8,13},3,FALSE)'],
+    ['Hello, World.', '=CONCATENATE("Hello, ", "World.")'],
+    ['{NON-EMPTY SET}', '=UPPER("{non-EMPTY set}")'], // braces not used for matrix
+    ['upper', '=LOWER(B1)'],
+    [false, '=and(B2,B3)'],
+    [0, '=acos(1)'],
+    [0.785398, '=round(atan({1,2,3}),6)'], // {1,2,3} will be flattened to 1
+    [2, '=minverse({-2.5,1.5;2,-1})'], // 2 is the flattened result of {2,3;4,5}
+    [4, '=MDETERM(MMULT({1,2;3,4},{5,6;7,8}))'], // multiple matrices
+    [110, '=SUM(A1,Sheet2!$A$1)'], // different sheet absolute address
+    [220, '=SUM(A2,A2B)'], // defined name on different sheet
+];
diff --git a/tests/data/Calculation/Information/ERROR_TYPE.php b/tests/data/Calculation/Information/ERROR_TYPE.php
index 45f279704b..3a3fb857b0 100644
--- a/tests/data/Calculation/Information/ERROR_TYPE.php
+++ b/tests/data/Calculation/Information/ERROR_TYPE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#N/A',
diff --git a/tests/data/Calculation/Information/IS_BLANK.php b/tests/data/Calculation/Information/IS_BLANK.php
index c2c9aec184..a439b4dcf8 100644
--- a/tests/data/Calculation/Information/IS_BLANK.php
+++ b/tests/data/Calculation/Information/IS_BLANK.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         true,
diff --git a/tests/data/Calculation/Information/IS_ERR.php b/tests/data/Calculation/Information/IS_ERR.php
index 2e73734734..894be27143 100644
--- a/tests/data/Calculation/Information/IS_ERR.php
+++ b/tests/data/Calculation/Information/IS_ERR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Calculation/Information/IS_ERROR.php b/tests/data/Calculation/Information/IS_ERROR.php
index 24e864fe99..39814fb947 100644
--- a/tests/data/Calculation/Information/IS_ERROR.php
+++ b/tests/data/Calculation/Information/IS_ERROR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Calculation/Information/IS_EVEN.php b/tests/data/Calculation/Information/IS_EVEN.php
index ad009b58d1..2bae506359 100644
--- a/tests/data/Calculation/Information/IS_EVEN.php
+++ b/tests/data/Calculation/Information/IS_EVEN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#NAME?',
diff --git a/tests/data/Calculation/Information/IS_LOGICAL.php b/tests/data/Calculation/Information/IS_LOGICAL.php
index e63fff9ba2..fcc15db8d0 100644
--- a/tests/data/Calculation/Information/IS_LOGICAL.php
+++ b/tests/data/Calculation/Information/IS_LOGICAL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Calculation/Information/IS_NA.php b/tests/data/Calculation/Information/IS_NA.php
index c5ebdf7987..672e777d35 100644
--- a/tests/data/Calculation/Information/IS_NA.php
+++ b/tests/data/Calculation/Information/IS_NA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Calculation/Information/IS_NONTEXT.php b/tests/data/Calculation/Information/IS_NONTEXT.php
index 2fd5872c34..ccde83be32 100644
--- a/tests/data/Calculation/Information/IS_NONTEXT.php
+++ b/tests/data/Calculation/Information/IS_NONTEXT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         true,
diff --git a/tests/data/Calculation/Information/IS_NUMBER.php b/tests/data/Calculation/Information/IS_NUMBER.php
index a9e33453f3..013f37f408 100644
--- a/tests/data/Calculation/Information/IS_NUMBER.php
+++ b/tests/data/Calculation/Information/IS_NUMBER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Calculation/Information/IS_ODD.php b/tests/data/Calculation/Information/IS_ODD.php
index 890bd6a275..cb4536acfe 100644
--- a/tests/data/Calculation/Information/IS_ODD.php
+++ b/tests/data/Calculation/Information/IS_ODD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#NAME?',
diff --git a/tests/data/Calculation/Information/IS_TEXT.php b/tests/data/Calculation/Information/IS_TEXT.php
index 998f8e27e5..68022948df 100644
--- a/tests/data/Calculation/Information/IS_TEXT.php
+++ b/tests/data/Calculation/Information/IS_TEXT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Calculation/Information/N.php b/tests/data/Calculation/Information/N.php
index 3fc527da31..bac301592d 100644
--- a/tests/data/Calculation/Information/N.php
+++ b/tests/data/Calculation/Information/N.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0,
diff --git a/tests/data/Calculation/Information/TYPE.php b/tests/data/Calculation/Information/TYPE.php
index c6aefb776a..9cbc59dd38 100644
--- a/tests/data/Calculation/Information/TYPE.php
+++ b/tests/data/Calculation/Information/TYPE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/Logical/AND.php b/tests/data/Calculation/Logical/AND.php
index 3d08a3a6a3..30a7e9d30b 100644
--- a/tests/data/Calculation/Logical/AND.php
+++ b/tests/data/Calculation/Logical/AND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => [
         'exception',
diff --git a/tests/data/Calculation/Logical/ANDLiteral.php b/tests/data/Calculation/Logical/ANDLiteral.php
index 0dff483bb7..0747f8a4a2 100644
--- a/tests/data/Calculation/Logical/ANDLiteral.php
+++ b/tests/data/Calculation/Logical/ANDLiteral.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'both boolean true' => [true, 'true, true'],
     'boolean and string-true' => [true, 'true, "true"'],
diff --git a/tests/data/Calculation/Logical/IF.php b/tests/data/Calculation/Logical/IF.php
index 3bf7d90f28..1f69d10995 100644
--- a/tests/data/Calculation/Logical/IF.php
+++ b/tests/data/Calculation/Logical/IF.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => [
         'exception',
diff --git a/tests/data/Calculation/Logical/IFERROR.php b/tests/data/Calculation/Logical/IFERROR.php
index a379a5fbf4..ebc6b40605 100644
--- a/tests/data/Calculation/Logical/IFERROR.php
+++ b/tests/data/Calculation/Logical/IFERROR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'empty cell treated as 0' => [
         0,
diff --git a/tests/data/Calculation/Logical/IFNA.php b/tests/data/Calculation/Logical/IFNA.php
index d7fb7193f2..4216212a02 100644
--- a/tests/data/Calculation/Logical/IFNA.php
+++ b/tests/data/Calculation/Logical/IFNA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         55,
diff --git a/tests/data/Calculation/Logical/IFS.php b/tests/data/Calculation/Logical/IFS.php
index d4dd607e43..2981e74c56 100644
--- a/tests/data/Calculation/Logical/IFS.php
+++ b/tests/data/Calculation/Logical/IFS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => ['exception'],
     [
diff --git a/tests/data/Calculation/Logical/NOT.php b/tests/data/Calculation/Logical/NOT.php
index 9936c26812..37b94968de 100644
--- a/tests/data/Calculation/Logical/NOT.php
+++ b/tests/data/Calculation/Logical/NOT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => [
         'exception',
diff --git a/tests/data/Calculation/Logical/OR.php b/tests/data/Calculation/Logical/OR.php
index c5317b3bcb..53aab19704 100644
--- a/tests/data/Calculation/Logical/OR.php
+++ b/tests/data/Calculation/Logical/OR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => [
         'exception',
diff --git a/tests/data/Calculation/Logical/ORLiteral.php b/tests/data/Calculation/Logical/ORLiteral.php
index 17f4988226..d8331d60ee 100644
--- a/tests/data/Calculation/Logical/ORLiteral.php
+++ b/tests/data/Calculation/Logical/ORLiteral.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'both boolean true' => [true, 'true, true'],
     'boolean or string-true' => [true, 'true, "true"'],
diff --git a/tests/data/Calculation/Logical/SWITCH.php b/tests/data/Calculation/Logical/SWITCH.php
index 689d1d8faa..724aa09dbf 100644
--- a/tests/data/Calculation/Logical/SWITCH.php
+++ b/tests/data/Calculation/Logical/SWITCH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'match value1 A result is C' => [
         'C',
diff --git a/tests/data/Calculation/Logical/XOR.php b/tests/data/Calculation/Logical/XOR.php
index 57a170a48c..52895d44b8 100644
--- a/tests/data/Calculation/Logical/XOR.php
+++ b/tests/data/Calculation/Logical/XOR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => [
         'exception',
diff --git a/tests/data/Calculation/Logical/XORLiteral.php b/tests/data/Calculation/Logical/XORLiteral.php
index a0c0be7073..086fb7e83c 100644
--- a/tests/data/Calculation/Logical/XORLiteral.php
+++ b/tests/data/Calculation/Logical/XORLiteral.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'both boolean true' => [false, 'true, true'],
     'boolean xor string-true' => [false, 'true, "true"'],
diff --git a/tests/data/Calculation/LookupRef/ADDRESS.php b/tests/data/Calculation/LookupRef/ADDRESS.php
index 14a3cf7db8..aaaada75a3 100644
--- a/tests/data/Calculation/LookupRef/ADDRESS.php
+++ b/tests/data/Calculation/LookupRef/ADDRESS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '$C$2',
diff --git a/tests/data/Calculation/LookupRef/CHOOSE.php b/tests/data/Calculation/LookupRef/CHOOSE.php
index 96c2978037..8d9ce259e3 100644
--- a/tests/data/Calculation/LookupRef/CHOOSE.php
+++ b/tests/data/Calculation/LookupRef/CHOOSE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'brown',
diff --git a/tests/data/Calculation/LookupRef/COLUMN.php b/tests/data/Calculation/LookupRef/COLUMN.php
index f5119ba821..ae6e8ead9f 100644
--- a/tests/data/Calculation/LookupRef/COLUMN.php
+++ b/tests/data/Calculation/LookupRef/COLUMN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/LookupRef/COLUMNS.php b/tests/data/Calculation/LookupRef/COLUMNS.php
index 3a6a587c4b..09dd0ca76a 100644
--- a/tests/data/Calculation/LookupRef/COLUMNS.php
+++ b/tests/data/Calculation/LookupRef/COLUMNS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/LookupRef/COLUMNSonSpreadsheet.php b/tests/data/Calculation/LookupRef/COLUMNSonSpreadsheet.php
index 4002c2f16d..76505334ba 100644
--- a/tests/data/Calculation/LookupRef/COLUMNSonSpreadsheet.php
+++ b/tests/data/Calculation/LookupRef/COLUMNSonSpreadsheet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'global $e$2-$e$6' => [1, 'namedrangex'],
     'global $f$2:$h$2' => [3, 'namedrangey'],
diff --git a/tests/data/Calculation/LookupRef/COLUMNonSpreadsheet.php b/tests/data/Calculation/LookupRef/COLUMNonSpreadsheet.php
index cc93653e80..16a43707cb 100644
--- a/tests/data/Calculation/LookupRef/COLUMNonSpreadsheet.php
+++ b/tests/data/Calculation/LookupRef/COLUMNonSpreadsheet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'current column' => [2, 'omitted'],
     'global name $E$2:$E$6' => [5, 'namedrangex'],
diff --git a/tests/data/Calculation/LookupRef/FORMULATEXT.php b/tests/data/Calculation/LookupRef/FORMULATEXT.php
index 46639c28cf..e5debe475a 100644
--- a/tests/data/Calculation/LookupRef/FORMULATEXT.php
+++ b/tests/data/Calculation/LookupRef/FORMULATEXT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#N/A',
diff --git a/tests/data/Calculation/LookupRef/HLOOKUP.php b/tests/data/Calculation/LookupRef/HLOOKUP.php
index 29546426b7..f822e99f86 100644
--- a/tests/data/Calculation/LookupRef/HLOOKUP.php
+++ b/tests/data/Calculation/LookupRef/HLOOKUP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 function orderGrid(): array
 {
     return [
diff --git a/tests/data/Calculation/LookupRef/HYPERLINK.php b/tests/data/Calculation/LookupRef/HYPERLINK.php
index 63ea4ed73f..3e27ca46e1 100644
--- a/tests/data/Calculation/LookupRef/HYPERLINK.php
+++ b/tests/data/Calculation/LookupRef/HYPERLINK.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/LookupRef/INDEX.php b/tests/data/Calculation/LookupRef/INDEX.php
index 4d4d1dad22..47c0fc9f0d 100644
--- a/tests/data/Calculation/LookupRef/INDEX.php
+++ b/tests/data/Calculation/LookupRef/INDEX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [20 => ['R' => 1]], // Expected
diff --git a/tests/data/Calculation/LookupRef/INDEXonSpreadsheet.php b/tests/data/Calculation/LookupRef/INDEXonSpreadsheet.php
index eff13722f3..76f6ddd464 100644
--- a/tests/data/Calculation/LookupRef/INDEXonSpreadsheet.php
+++ b/tests/data/Calculation/LookupRef/INDEXonSpreadsheet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'Single Cell' => [
         1, // Expected
diff --git a/tests/data/Calculation/LookupRef/INDIRECT.php b/tests/data/Calculation/LookupRef/INDIRECT.php
index 7dc2515a31..77554ec85e 100644
--- a/tests/data/Calculation/LookupRef/INDIRECT.php
+++ b/tests/data/Calculation/LookupRef/INDIRECT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'cell range absolute' => [600, '$A$1:$A$3'],
     'cell range on different sheet' => [30, 'OtherSheet!A1:A2'],
diff --git a/tests/data/Calculation/LookupRef/LOOKUP.php b/tests/data/Calculation/LookupRef/LOOKUP.php
index 9c7d96eb01..84e3e27855 100644
--- a/tests/data/Calculation/LookupRef/LOOKUP.php
+++ b/tests/data/Calculation/LookupRef/LOOKUP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [ // Office reference example #1
         'orange',
diff --git a/tests/data/Calculation/LookupRef/MATCH.php b/tests/data/Calculation/LookupRef/MATCH.php
index 19d84a89da..02c9f0737d 100644
--- a/tests/data/Calculation/LookupRef/MATCH.php
+++ b/tests/data/Calculation/LookupRef/MATCH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'unsorted numeric array still finds match with type 1?' => [
         2, // Expected
diff --git a/tests/data/Calculation/LookupRef/OFFSET.php b/tests/data/Calculation/LookupRef/OFFSET.php
index 9c2f52c1de..53706dd1f3 100644
--- a/tests/data/Calculation/LookupRef/OFFSET.php
+++ b/tests/data/Calculation/LookupRef/OFFSET.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#VALUE!',
diff --git a/tests/data/Calculation/LookupRef/ROW.php b/tests/data/Calculation/LookupRef/ROW.php
index d6092f7ffb..55f02aecd6 100644
--- a/tests/data/Calculation/LookupRef/ROW.php
+++ b/tests/data/Calculation/LookupRef/ROW.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/LookupRef/ROWS.php b/tests/data/Calculation/LookupRef/ROWS.php
index 9380829966..c30f11d215 100644
--- a/tests/data/Calculation/LookupRef/ROWS.php
+++ b/tests/data/Calculation/LookupRef/ROWS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/LookupRef/ROWSonSpreadsheet.php b/tests/data/Calculation/LookupRef/ROWSonSpreadsheet.php
index 117885bc13..0c0936c86d 100644
--- a/tests/data/Calculation/LookupRef/ROWSonSpreadsheet.php
+++ b/tests/data/Calculation/LookupRef/ROWSonSpreadsheet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'global $E$2:$E$6' => [5, 'namedrangex'],
     'global $F$2:$H$2' => [1, 'namedrangey'],
diff --git a/tests/data/Calculation/LookupRef/ROWonSpreadsheet.php b/tests/data/Calculation/LookupRef/ROWonSpreadsheet.php
index f2395e6b74..0250934df0 100644
--- a/tests/data/Calculation/LookupRef/ROWonSpreadsheet.php
+++ b/tests/data/Calculation/LookupRef/ROWonSpreadsheet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'current row' => [3, 'omitted'],
     'global name $E$2:$E$6' => [2, 'namedrangex'],
diff --git a/tests/data/Calculation/LookupRef/TRANSPOSE.php b/tests/data/Calculation/LookupRef/TRANSPOSE.php
index a5ca45f48f..1f75ff1254 100644
--- a/tests/data/Calculation/LookupRef/TRANSPOSE.php
+++ b/tests/data/Calculation/LookupRef/TRANSPOSE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/Calculation/LookupRef/VLOOKUP.php b/tests/data/Calculation/LookupRef/VLOOKUP.php
index 8ebbb2e9fa..c2398f209e 100644
--- a/tests/data/Calculation/LookupRef/VLOOKUP.php
+++ b/tests/data/Calculation/LookupRef/VLOOKUP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 function densityGrid(): array
 {
     return [
diff --git a/tests/data/Calculation/MathTrig/ABS.php b/tests/data/Calculation/MathTrig/ABS.php
index 4082ceebe1..e640498082 100644
--- a/tests/data/Calculation/MathTrig/ABS.php
+++ b/tests/data/Calculation/MathTrig/ABS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception - not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/ACOS.php b/tests/data/Calculation/MathTrig/ACOS.php
index 487a0628a0..ca4621873f 100644
--- a/tests/data/Calculation/MathTrig/ACOS.php
+++ b/tests/data/Calculation/MathTrig/ACOS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/ACOSH.php b/tests/data/Calculation/MathTrig/ACOSH.php
index 9452be9369..b5f391ac22 100644
--- a/tests/data/Calculation/MathTrig/ACOSH.php
+++ b/tests/data/Calculation/MathTrig/ACOSH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/ACOT.php b/tests/data/Calculation/MathTrig/ACOT.php
index 7d654c088f..0a6432924b 100644
--- a/tests/data/Calculation/MathTrig/ACOT.php
+++ b/tests/data/Calculation/MathTrig/ACOT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [3.04192400109863, -10],
diff --git a/tests/data/Calculation/MathTrig/ACOTH.php b/tests/data/Calculation/MathTrig/ACOTH.php
index cf5639b407..4f3d6383d6 100644
--- a/tests/data/Calculation/MathTrig/ACOTH.php
+++ b/tests/data/Calculation/MathTrig/ACOTH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [-0.10033534773108, -10],
diff --git a/tests/data/Calculation/MathTrig/ARABIC.php b/tests/data/Calculation/MathTrig/ARABIC.php
index e2a6f46bfd..f3dce71e4b 100644
--- a/tests/data/Calculation/MathTrig/ARABIC.php
+++ b/tests/data/Calculation/MathTrig/ARABIC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0,
diff --git a/tests/data/Calculation/MathTrig/ASIN.php b/tests/data/Calculation/MathTrig/ASIN.php
index 1e874a8597..9e20c0437d 100644
--- a/tests/data/Calculation/MathTrig/ASIN.php
+++ b/tests/data/Calculation/MathTrig/ASIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/ASINH.php b/tests/data/Calculation/MathTrig/ASINH.php
index 27bf98e654..2455964e6f 100644
--- a/tests/data/Calculation/MathTrig/ASINH.php
+++ b/tests/data/Calculation/MathTrig/ASINH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/ATAN.php b/tests/data/Calculation/MathTrig/ATAN.php
index 1b1fc4aeb2..b9928e8ae2 100644
--- a/tests/data/Calculation/MathTrig/ATAN.php
+++ b/tests/data/Calculation/MathTrig/ATAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/ATAN2.php b/tests/data/Calculation/MathTrig/ATAN2.php
index b4ec202f18..d8048bd150 100644
--- a/tests/data/Calculation/MathTrig/ATAN2.php
+++ b/tests/data/Calculation/MathTrig/ATAN2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // x_num, y_num, Result
 
 return [
diff --git a/tests/data/Calculation/MathTrig/ATANH.php b/tests/data/Calculation/MathTrig/ATANH.php
index e43a1bd0f9..336b4074f4 100644
--- a/tests/data/Calculation/MathTrig/ATANH.php
+++ b/tests/data/Calculation/MathTrig/ATANH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/BASE.php b/tests/data/Calculation/MathTrig/BASE.php
index 1f67fe2a87..b913f9aa42 100644
--- a/tests/data/Calculation/MathTrig/BASE.php
+++ b/tests/data/Calculation/MathTrig/BASE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '111',
diff --git a/tests/data/Calculation/MathTrig/CEILING.php b/tests/data/Calculation/MathTrig/CEILING.php
index a4af7df1cd..c2adf59a6e 100644
--- a/tests/data/Calculation/MathTrig/CEILING.php
+++ b/tests/data/Calculation/MathTrig/CEILING.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [3.0, '2.5, 1'],
     [-4.0, '-2.5, -2'],
diff --git a/tests/data/Calculation/MathTrig/CEILINGMATH.php b/tests/data/Calculation/MathTrig/CEILINGMATH.php
index ea50d6e1a6..50734a974c 100644
--- a/tests/data/Calculation/MathTrig/CEILINGMATH.php
+++ b/tests/data/Calculation/MathTrig/CEILINGMATH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [3, '2.5, 1'],
     [-2, '"-2.5", "-2"'],
diff --git a/tests/data/Calculation/MathTrig/CEILINGPRECISE.php b/tests/data/Calculation/MathTrig/CEILINGPRECISE.php
index dfeada23cc..51bea6986c 100644
--- a/tests/data/Calculation/MathTrig/CEILINGPRECISE.php
+++ b/tests/data/Calculation/MathTrig/CEILINGPRECISE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [3, '2.5, 1'],
     [-2, '-2.5, -2'],
diff --git a/tests/data/Calculation/MathTrig/COMBIN.php b/tests/data/Calculation/MathTrig/COMBIN.php
index d163e8836b..a7044e2759 100644
--- a/tests/data/Calculation/MathTrig/COMBIN.php
+++ b/tests/data/Calculation/MathTrig/COMBIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // NumObjs, NumInSet, Result
 
 return [
diff --git a/tests/data/Calculation/MathTrig/COMBINA.php b/tests/data/Calculation/MathTrig/COMBINA.php
index c5a26a5f2e..bc81207be5 100644
--- a/tests/data/Calculation/MathTrig/COMBINA.php
+++ b/tests/data/Calculation/MathTrig/COMBINA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // NumObjs, NumInSet, Result
 
 return [
diff --git a/tests/data/Calculation/MathTrig/COS.php b/tests/data/Calculation/MathTrig/COS.php
index 9254fe58c6..497b903f77 100644
--- a/tests/data/Calculation/MathTrig/COS.php
+++ b/tests/data/Calculation/MathTrig/COS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/COSH.php b/tests/data/Calculation/MathTrig/COSH.php
index 7057e92128..09d2e78724 100644
--- a/tests/data/Calculation/MathTrig/COSH.php
+++ b/tests/data/Calculation/MathTrig/COSH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/COT.php b/tests/data/Calculation/MathTrig/COT.php
index 497acac9d3..19d63eb217 100644
--- a/tests/data/Calculation/MathTrig/COT.php
+++ b/tests/data/Calculation/MathTrig/COT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [-1.54235104535692, -10],
diff --git a/tests/data/Calculation/MathTrig/COTH.php b/tests/data/Calculation/MathTrig/COTH.php
index 218292d282..804f01c76a 100644
--- a/tests/data/Calculation/MathTrig/COTH.php
+++ b/tests/data/Calculation/MathTrig/COTH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [-1.00000000412231, -10],
diff --git a/tests/data/Calculation/MathTrig/CSC.php b/tests/data/Calculation/MathTrig/CSC.php
index 54d974487e..1a82137350 100644
--- a/tests/data/Calculation/MathTrig/CSC.php
+++ b/tests/data/Calculation/MathTrig/CSC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [1.83816396088967, -10],
diff --git a/tests/data/Calculation/MathTrig/CSCH.php b/tests/data/Calculation/MathTrig/CSCH.php
index c94a013f46..3e6304c457 100644
--- a/tests/data/Calculation/MathTrig/CSCH.php
+++ b/tests/data/Calculation/MathTrig/CSCH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [-0.00009079985971, -10],
diff --git a/tests/data/Calculation/MathTrig/DEGREES.php b/tests/data/Calculation/MathTrig/DEGREES.php
index 04be2d8256..5aa78f9de2 100644
--- a/tests/data/Calculation/MathTrig/DEGREES.php
+++ b/tests/data/Calculation/MathTrig/DEGREES.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/EVEN.php b/tests/data/Calculation/MathTrig/EVEN.php
index ff44f0d6c8..9f8160ebe6 100644
--- a/tests/data/Calculation/MathTrig/EVEN.php
+++ b/tests/data/Calculation/MathTrig/EVEN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0, 'null'],
     [6, 5.4],
diff --git a/tests/data/Calculation/MathTrig/EXP.php b/tests/data/Calculation/MathTrig/EXP.php
index f9845ea3ab..8eade8dbba 100644
--- a/tests/data/Calculation/MathTrig/EXP.php
+++ b/tests/data/Calculation/MathTrig/EXP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/FACT.php b/tests/data/Calculation/MathTrig/FACT.php
index c789ced8b7..20175e0d6e 100644
--- a/tests/data/Calculation/MathTrig/FACT.php
+++ b/tests/data/Calculation/MathTrig/FACT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         120,
diff --git a/tests/data/Calculation/MathTrig/FACTDOUBLE.php b/tests/data/Calculation/MathTrig/FACTDOUBLE.php
index 34a3403f9a..e5e8fd8ad2 100644
--- a/tests/data/Calculation/MathTrig/FACTDOUBLE.php
+++ b/tests/data/Calculation/MathTrig/FACTDOUBLE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/MathTrig/FACTGNUMERIC.php b/tests/data/Calculation/MathTrig/FACTGNUMERIC.php
index 0f040dd02f..de70cf17e2 100644
--- a/tests/data/Calculation/MathTrig/FACTGNUMERIC.php
+++ b/tests/data/Calculation/MathTrig/FACTGNUMERIC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         120,
diff --git a/tests/data/Calculation/MathTrig/FLOOR.php b/tests/data/Calculation/MathTrig/FLOOR.php
index 442f7c9f4a..ec2aa87f83 100644
--- a/tests/data/Calculation/MathTrig/FLOOR.php
+++ b/tests/data/Calculation/MathTrig/FLOOR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [2, '2.5, 1'],
     [-2, '-2.5, -2'],
diff --git a/tests/data/Calculation/MathTrig/FLOORMATH.php b/tests/data/Calculation/MathTrig/FLOORMATH.php
index e871c5295a..d8b1303fba 100644
--- a/tests/data/Calculation/MathTrig/FLOORMATH.php
+++ b/tests/data/Calculation/MathTrig/FLOORMATH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [2, '2.5, 1'],
     [-4, '"-2.5", "-2"'],
diff --git a/tests/data/Calculation/MathTrig/FLOORPRECISE.php b/tests/data/Calculation/MathTrig/FLOORPRECISE.php
index 8cc2c0432f..73f13ceb21 100644
--- a/tests/data/Calculation/MathTrig/FLOORPRECISE.php
+++ b/tests/data/Calculation/MathTrig/FLOORPRECISE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [2, '2.5, 1'],
     [-4, '-2.5, -2'],
diff --git a/tests/data/Calculation/MathTrig/GCD.php b/tests/data/Calculation/MathTrig/GCD.php
index 7ace4bc67e..016f24fe70 100644
--- a/tests/data/Calculation/MathTrig/GCD.php
+++ b/tests/data/Calculation/MathTrig/GCD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/Calculation/MathTrig/INT.php b/tests/data/Calculation/MathTrig/INT.php
index ee6740f779..09ce759183 100644
--- a/tests/data/Calculation/MathTrig/INT.php
+++ b/tests/data/Calculation/MathTrig/INT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     [5, '5.4'],
diff --git a/tests/data/Calculation/MathTrig/LCM.php b/tests/data/Calculation/MathTrig/LCM.php
index 92a8917569..995921d74e 100644
--- a/tests/data/Calculation/MathTrig/LCM.php
+++ b/tests/data/Calculation/MathTrig/LCM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         10,
diff --git a/tests/data/Calculation/MathTrig/LN.php b/tests/data/Calculation/MathTrig/LN.php
index 3bcd8b6c89..197381a191 100644
--- a/tests/data/Calculation/MathTrig/LN.php
+++ b/tests/data/Calculation/MathTrig/LN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/LOG.php b/tests/data/Calculation/MathTrig/LOG.php
index 4e52e87594..43013f303e 100644
--- a/tests/data/Calculation/MathTrig/LOG.php
+++ b/tests/data/Calculation/MathTrig/LOG.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // number, base, result
 
 return [
diff --git a/tests/data/Calculation/MathTrig/LOG10.php b/tests/data/Calculation/MathTrig/LOG10.php
index 72869559ac..8afc2cc351 100644
--- a/tests/data/Calculation/MathTrig/LOG10.php
+++ b/tests/data/Calculation/MathTrig/LOG10.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/MDETERM.php b/tests/data/Calculation/MathTrig/MDETERM.php
index b26d04d730..076b1e46f0 100644
--- a/tests/data/Calculation/MathTrig/MDETERM.php
+++ b/tests/data/Calculation/MathTrig/MDETERM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0,
diff --git a/tests/data/Calculation/MathTrig/MINVERSE.php b/tests/data/Calculation/MathTrig/MINVERSE.php
index 89feae1aef..99a39ce390 100644
--- a/tests/data/Calculation/MathTrig/MINVERSE.php
+++ b/tests/data/Calculation/MathTrig/MINVERSE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/Calculation/MathTrig/MMULT.php b/tests/data/Calculation/MathTrig/MMULT.php
index 7b424d589f..c50cc8f27c 100644
--- a/tests/data/Calculation/MathTrig/MMULT.php
+++ b/tests/data/Calculation/MathTrig/MMULT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/Calculation/MathTrig/MOD.php b/tests/data/Calculation/MathTrig/MOD.php
index e53383d1b4..dafc016bc1 100644
--- a/tests/data/Calculation/MathTrig/MOD.php
+++ b/tests/data/Calculation/MathTrig/MOD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2,
diff --git a/tests/data/Calculation/MathTrig/MROUND.php b/tests/data/Calculation/MathTrig/MROUND.php
index aeb8c1d672..9a73840104 100644
--- a/tests/data/Calculation/MathTrig/MROUND.php
+++ b/tests/data/Calculation/MathTrig/MROUND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [9, '10,3'],
     [-9, '-10,-3'],
diff --git a/tests/data/Calculation/MathTrig/MULTINOMIAL.php b/tests/data/Calculation/MathTrig/MULTINOMIAL.php
index e56d341d36..eabb68d154 100644
--- a/tests/data/Calculation/MathTrig/MULTINOMIAL.php
+++ b/tests/data/Calculation/MathTrig/MULTINOMIAL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1260,
diff --git a/tests/data/Calculation/MathTrig/ODD.php b/tests/data/Calculation/MathTrig/ODD.php
index ae18067752..7c1abfa871 100644
--- a/tests/data/Calculation/MathTrig/ODD.php
+++ b/tests/data/Calculation/MathTrig/ODD.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [1, 'null'],
     [7, 5.4],
diff --git a/tests/data/Calculation/MathTrig/POWER.php b/tests/data/Calculation/MathTrig/POWER.php
index 16c8c2efed..a89e202d2d 100644
--- a/tests/data/Calculation/MathTrig/POWER.php
+++ b/tests/data/Calculation/MathTrig/POWER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#NUM!',
diff --git a/tests/data/Calculation/MathTrig/PRODUCT.php b/tests/data/Calculation/MathTrig/PRODUCT.php
index 657c713c0d..67e36ee515 100644
--- a/tests/data/Calculation/MathTrig/PRODUCT.php
+++ b/tests/data/Calculation/MathTrig/PRODUCT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2250,
diff --git a/tests/data/Calculation/MathTrig/QUOTIENT.php b/tests/data/Calculation/MathTrig/QUOTIENT.php
index 4190bde65e..1ba0f5eefb 100644
--- a/tests/data/Calculation/MathTrig/QUOTIENT.php
+++ b/tests/data/Calculation/MathTrig/QUOTIENT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2,
diff --git a/tests/data/Calculation/MathTrig/RADIANS.php b/tests/data/Calculation/MathTrig/RADIANS.php
index 9d03b8d950..517ff57bf1 100644
--- a/tests/data/Calculation/MathTrig/RADIANS.php
+++ b/tests/data/Calculation/MathTrig/RADIANS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/RANDBETWEEN.php b/tests/data/Calculation/MathTrig/RANDBETWEEN.php
index 4278b67af2..758400d4f1 100644
--- a/tests/data/Calculation/MathTrig/RANDBETWEEN.php
+++ b/tests/data/Calculation/MathTrig/RANDBETWEEN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', 'y', 3],
     ['#VALUE!', 3, 'y'],
diff --git a/tests/data/Calculation/MathTrig/ROMAN.php b/tests/data/Calculation/MathTrig/ROMAN.php
index d73868ca66..130dc717e8 100644
--- a/tests/data/Calculation/MathTrig/ROMAN.php
+++ b/tests/data/Calculation/MathTrig/ROMAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['XLIX', '49'],
     ['L', '50'],
diff --git a/tests/data/Calculation/MathTrig/ROUND.php b/tests/data/Calculation/MathTrig/ROUND.php
index 4cdc02f223..3a2d0a2f05 100644
--- a/tests/data/Calculation/MathTrig/ROUND.php
+++ b/tests/data/Calculation/MathTrig/ROUND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0, '0,2'],
     [663, '662.79, 0'],
diff --git a/tests/data/Calculation/MathTrig/ROUNDDOWN.php b/tests/data/Calculation/MathTrig/ROUNDDOWN.php
index 5881aa0eef..3a65c13f24 100644
--- a/tests/data/Calculation/MathTrig/ROUNDDOWN.php
+++ b/tests/data/Calculation/MathTrig/ROUNDDOWN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0, '0,2'],
     [662, '662.79,0'],
diff --git a/tests/data/Calculation/MathTrig/ROUNDUP.php b/tests/data/Calculation/MathTrig/ROUNDUP.php
index 07c5eacbb3..9014a9e3c0 100644
--- a/tests/data/Calculation/MathTrig/ROUNDUP.php
+++ b/tests/data/Calculation/MathTrig/ROUNDUP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0, '0,2'],
     [663, '662.79, 0'],
diff --git a/tests/data/Calculation/MathTrig/SEC.php b/tests/data/Calculation/MathTrig/SEC.php
index 13dcd5b221..c46ff697b0 100644
--- a/tests/data/Calculation/MathTrig/SEC.php
+++ b/tests/data/Calculation/MathTrig/SEC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [-1.1917935066879, -10],
diff --git a/tests/data/Calculation/MathTrig/SECH.php b/tests/data/Calculation/MathTrig/SECH.php
index 38bb128ec2..7e3887bda0 100644
--- a/tests/data/Calculation/MathTrig/SECH.php
+++ b/tests/data/Calculation/MathTrig/SECH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['#VALUE!', '"ABC"'],
     [0.00009079985934, -10],
diff --git a/tests/data/Calculation/MathTrig/SEQUENCE.php b/tests/data/Calculation/MathTrig/SEQUENCE.php
index 49c9010221..6ae7fb4332 100644
--- a/tests/data/Calculation/MathTrig/SEQUENCE.php
+++ b/tests/data/Calculation/MathTrig/SEQUENCE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [2, 2],
diff --git a/tests/data/Calculation/MathTrig/SERIESSUM.php b/tests/data/Calculation/MathTrig/SERIESSUM.php
index 2163dab748..66df98b834 100644
--- a/tests/data/Calculation/MathTrig/SERIESSUM.php
+++ b/tests/data/Calculation/MathTrig/SERIESSUM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3905,
diff --git a/tests/data/Calculation/MathTrig/SIGN.php b/tests/data/Calculation/MathTrig/SIGN.php
index fab57c808a..91da4e2c85 100644
--- a/tests/data/Calculation/MathTrig/SIGN.php
+++ b/tests/data/Calculation/MathTrig/SIGN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [-1, -1.5],
     [-1, -1],
diff --git a/tests/data/Calculation/MathTrig/SIN.php b/tests/data/Calculation/MathTrig/SIN.php
index 7518aae2d0..62455b4a0f 100644
--- a/tests/data/Calculation/MathTrig/SIN.php
+++ b/tests/data/Calculation/MathTrig/SIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/SINH.php b/tests/data/Calculation/MathTrig/SINH.php
index 7d9091440e..f856f2c1cf 100644
--- a/tests/data/Calculation/MathTrig/SINH.php
+++ b/tests/data/Calculation/MathTrig/SINH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/SQRT.php b/tests/data/Calculation/MathTrig/SQRT.php
index f54038f81e..79fb417e89 100644
--- a/tests/data/Calculation/MathTrig/SQRT.php
+++ b/tests/data/Calculation/MathTrig/SQRT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception'], // exception not enough args
     ['#VALUE!', 'ABC'],
diff --git a/tests/data/Calculation/MathTrig/SQRTPI.php b/tests/data/Calculation/MathTrig/SQRTPI.php
index 9f4c057f47..49190fdf92 100644
--- a/tests/data/Calculation/MathTrig/SQRTPI.php
+++ b/tests/data/Calculation/MathTrig/SQRTPI.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#VALUE!',
diff --git a/tests/data/Calculation/MathTrig/SUBTOTAL.php b/tests/data/Calculation/MathTrig/SUBTOTAL.php
index 8ba16df255..64e44f4237 100644
--- a/tests/data/Calculation/MathTrig/SUBTOTAL.php
+++ b/tests/data/Calculation/MathTrig/SUBTOTAL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [19.3333333333333, 1],
     [12, 2],
diff --git a/tests/data/Calculation/MathTrig/SUBTOTALHIDDEN.php b/tests/data/Calculation/MathTrig/SUBTOTALHIDDEN.php
index df6375dcc3..f12a07a059 100644
--- a/tests/data/Calculation/MathTrig/SUBTOTALHIDDEN.php
+++ b/tests/data/Calculation/MathTrig/SUBTOTALHIDDEN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [21, 101],
     [5, 102],
diff --git a/tests/data/Calculation/MathTrig/SUM.php b/tests/data/Calculation/MathTrig/SUM.php
index ad2c78e0ce..f3c5c265f0 100644
--- a/tests/data/Calculation/MathTrig/SUM.php
+++ b/tests/data/Calculation/MathTrig/SUM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [50, 5, 15, 30],
     [52, 5, 15, 30, 2],
diff --git a/tests/data/Calculation/MathTrig/SUMIF.php b/tests/data/Calculation/MathTrig/SUMIF.php
index bb5d6aa120..ff9dd4dfaa 100644
--- a/tests/data/Calculation/MathTrig/SUMIF.php
+++ b/tests/data/Calculation/MathTrig/SUMIF.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         15,
diff --git a/tests/data/Calculation/MathTrig/SUMIFS.php b/tests/data/Calculation/MathTrig/SUMIFS.php
index 9d860c30aa..2e3ab0a26c 100644
--- a/tests/data/Calculation/MathTrig/SUMIFS.php
+++ b/tests/data/Calculation/MathTrig/SUMIFS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0,
diff --git a/tests/data/Calculation/MathTrig/SUMLITERALS.php b/tests/data/Calculation/MathTrig/SUMLITERALS.php
index 0ea5938617..8c1a6df352 100644
--- a/tests/data/Calculation/MathTrig/SUMLITERALS.php
+++ b/tests/data/Calculation/MathTrig/SUMLITERALS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [50, '5, 15, 30'],
     [52, '5, 15, 30, 2'],
diff --git a/tests/data/Calculation/MathTrig/SUMPRODUCT.php b/tests/data/Calculation/MathTrig/SUMPRODUCT.php
index 14ea8b3974..06a3e7def9 100644
--- a/tests/data/Calculation/MathTrig/SUMPRODUCT.php
+++ b/tests/data/Calculation/MathTrig/SUMPRODUCT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         29,
diff --git a/tests/data/Calculation/MathTrig/SUMSQ.php b/tests/data/Calculation/MathTrig/SUMSQ.php
index f62e802a43..96869c0f67 100644
--- a/tests/data/Calculation/MathTrig/SUMSQ.php
+++ b/tests/data/Calculation/MathTrig/SUMSQ.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         25,
diff --git a/tests/data/Calculation/MathTrig/SUMWITHINDEXMATCH.php b/tests/data/Calculation/MathTrig/SUMWITHINDEXMATCH.php
index 35555830ee..db7685d6eb 100644
--- a/tests/data/Calculation/MathTrig/SUMWITHINDEXMATCH.php
+++ b/tests/data/Calculation/MathTrig/SUMWITHINDEXMATCH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         64, '=SUM(4 * INDEX(Lookup!B2, MATCH(A2, Lookup!A2, 0)))',
diff --git a/tests/data/Calculation/MathTrig/SUMX2MY2.php b/tests/data/Calculation/MathTrig/SUMX2MY2.php
index 725910f18a..f5badc8c56 100644
--- a/tests/data/Calculation/MathTrig/SUMX2MY2.php
+++ b/tests/data/Calculation/MathTrig/SUMX2MY2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         12,
diff --git a/tests/data/Calculation/MathTrig/SUMX2PY2.php b/tests/data/Calculation/MathTrig/SUMX2PY2.php
index 68d0ebf793..1ddd64d343 100644
--- a/tests/data/Calculation/MathTrig/SUMX2PY2.php
+++ b/tests/data/Calculation/MathTrig/SUMX2PY2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         64,
diff --git a/tests/data/Calculation/MathTrig/SUMXMY2.php b/tests/data/Calculation/MathTrig/SUMXMY2.php
index 0a7724db9b..cbae0efff3 100644
--- a/tests/data/Calculation/MathTrig/SUMXMY2.php
+++ b/tests/data/Calculation/MathTrig/SUMXMY2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         6,
diff --git a/tests/data/Calculation/MathTrig/TAN.php b/tests/data/Calculation/MathTrig/TAN.php
index 9b5e4f7409..cbba7ee300 100644
--- a/tests/data/Calculation/MathTrig/TAN.php
+++ b/tests/data/Calculation/MathTrig/TAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/TANH.php b/tests/data/Calculation/MathTrig/TANH.php
index 8b8d428bdd..0721b1b5bb 100644
--- a/tests/data/Calculation/MathTrig/TANH.php
+++ b/tests/data/Calculation/MathTrig/TANH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['exception', ''],
     ['#VALUE!', '"ABC"'],
diff --git a/tests/data/Calculation/MathTrig/TRUNC.php b/tests/data/Calculation/MathTrig/TRUNC.php
index f24c38bd8d..40fa521603 100644
--- a/tests/data/Calculation/MathTrig/TRUNC.php
+++ b/tests/data/Calculation/MathTrig/TRUNC.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [3.14, '3.14159, 2'],
     [3.141, '3.14159,  3'],
diff --git a/tests/data/Calculation/Statistical/AVEDEV.php b/tests/data/Calculation/Statistical/AVEDEV.php
index 7ae7360a05..c7968c3d93 100644
--- a/tests/data/Calculation/Statistical/AVEDEV.php
+++ b/tests/data/Calculation/Statistical/AVEDEV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1.020408163265,
diff --git a/tests/data/Calculation/Statistical/AVERAGE.php b/tests/data/Calculation/Statistical/AVERAGE.php
index 0cd8c4a704..dccd6fef73 100644
--- a/tests/data/Calculation/Statistical/AVERAGE.php
+++ b/tests/data/Calculation/Statistical/AVERAGE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         11,
diff --git a/tests/data/Calculation/Statistical/AVERAGEA.php b/tests/data/Calculation/Statistical/AVERAGEA.php
index bb5e192c36..407f28f2b7 100644
--- a/tests/data/Calculation/Statistical/AVERAGEA.php
+++ b/tests/data/Calculation/Statistical/AVERAGEA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         7.0,
diff --git a/tests/data/Calculation/Statistical/AVERAGEIF.php b/tests/data/Calculation/Statistical/AVERAGEIF.php
index 736b833fab..1c3848deb4 100644
--- a/tests/data/Calculation/Statistical/AVERAGEIF.php
+++ b/tests/data/Calculation/Statistical/AVERAGEIF.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         14000,
diff --git a/tests/data/Calculation/Statistical/AVERAGEIFS.php b/tests/data/Calculation/Statistical/AVERAGEIFS.php
index 8c62a09530..46c16ecd0c 100644
--- a/tests/data/Calculation/Statistical/AVERAGEIFS.php
+++ b/tests/data/Calculation/Statistical/AVERAGEIFS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no argument' => [
         'exception',
diff --git a/tests/data/Calculation/Statistical/BETADIST.php b/tests/data/Calculation/Statistical/BETADIST.php
index ef89575fdd..92b61fc5ae 100644
--- a/tests/data/Calculation/Statistical/BETADIST.php
+++ b/tests/data/Calculation/Statistical/BETADIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.4059136,
diff --git a/tests/data/Calculation/Statistical/BETAINV.php b/tests/data/Calculation/Statistical/BETAINV.php
index 609c280491..378dd91979 100644
--- a/tests/data/Calculation/Statistical/BETAINV.php
+++ b/tests/data/Calculation/Statistical/BETAINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1.862243320728,
diff --git a/tests/data/Calculation/Statistical/BINOMDIST.php b/tests/data/Calculation/Statistical/BINOMDIST.php
index 3606bced5c..e490729255 100644
--- a/tests/data/Calculation/Statistical/BINOMDIST.php
+++ b/tests/data/Calculation/Statistical/BINOMDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.706399436132,
diff --git a/tests/data/Calculation/Statistical/BINOMDISTRANGE.php b/tests/data/Calculation/Statistical/BINOMDISTRANGE.php
index 153706d157..56b2d315a1 100644
--- a/tests/data/Calculation/Statistical/BINOMDISTRANGE.php
+++ b/tests/data/Calculation/Statistical/BINOMDISTRANGE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.083974967429,
diff --git a/tests/data/Calculation/Statistical/BINOMINV.php b/tests/data/Calculation/Statistical/BINOMINV.php
index 2f73e29b02..b3d2446d82 100644
--- a/tests/data/Calculation/Statistical/BINOMINV.php
+++ b/tests/data/Calculation/Statistical/BINOMINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         32,
diff --git a/tests/data/Calculation/Statistical/BasicCOUNT.php b/tests/data/Calculation/Statistical/BasicCOUNT.php
index 4e1d31b065..ab7107835e 100644
--- a/tests/data/Calculation/Statistical/BasicCOUNT.php
+++ b/tests/data/Calculation/Statistical/BasicCOUNT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Shared\Date;
 
 return [
diff --git a/tests/data/Calculation/Statistical/CHIDISTLeftTail.php b/tests/data/Calculation/Statistical/CHIDISTLeftTail.php
index 313061ac99..a400b254c9 100644
--- a/tests/data/Calculation/Statistical/CHIDISTLeftTail.php
+++ b/tests/data/Calculation/Statistical/CHIDISTLeftTail.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.520499877813,
diff --git a/tests/data/Calculation/Statistical/CHIDISTRightTail.php b/tests/data/Calculation/Statistical/CHIDISTRightTail.php
index 24ddab9f8f..51293a36f3 100644
--- a/tests/data/Calculation/Statistical/CHIDISTRightTail.php
+++ b/tests/data/Calculation/Statistical/CHIDISTRightTail.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.964294972685,
diff --git a/tests/data/Calculation/Statistical/CHIINVLeftTail.php b/tests/data/Calculation/Statistical/CHIINVLeftTail.php
index bc64721e0c..0be08a847a 100644
--- a/tests/data/Calculation/Statistical/CHIINVLeftTail.php
+++ b/tests/data/Calculation/Statistical/CHIINVLeftTail.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         4.671330448981,
diff --git a/tests/data/Calculation/Statistical/CHIINVRightTail.php b/tests/data/Calculation/Statistical/CHIINVRightTail.php
index 58b317e59e..adeb7e3970 100644
--- a/tests/data/Calculation/Statistical/CHIINVRightTail.php
+++ b/tests/data/Calculation/Statistical/CHIINVRightTail.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         8.383430828608,
diff --git a/tests/data/Calculation/Statistical/CHITEST.php b/tests/data/Calculation/Statistical/CHITEST.php
index 6f5cd05c6f..b32a86ea90 100644
--- a/tests/data/Calculation/Statistical/CHITEST.php
+++ b/tests/data/Calculation/Statistical/CHITEST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.0152703571482,
diff --git a/tests/data/Calculation/Statistical/CONFIDENCE.php b/tests/data/Calculation/Statistical/CONFIDENCE.php
index 8fd68abc8c..f36898b4ec 100644
--- a/tests/data/Calculation/Statistical/CONFIDENCE.php
+++ b/tests/data/Calculation/Statistical/CONFIDENCE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.692951912734,
diff --git a/tests/data/Calculation/Statistical/CORREL.php b/tests/data/Calculation/Statistical/CORREL.php
index 409abbd6df..2f3d139bf4 100644
--- a/tests/data/Calculation/Statistical/CORREL.php
+++ b/tests/data/Calculation/Statistical/CORREL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.997054485502,
diff --git a/tests/data/Calculation/Statistical/COUNTA.php b/tests/data/Calculation/Statistical/COUNTA.php
index b6a9bd9442..de27193b06 100644
--- a/tests/data/Calculation/Statistical/COUNTA.php
+++ b/tests/data/Calculation/Statistical/COUNTA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Shared\Date;
 
 return [
diff --git a/tests/data/Calculation/Statistical/COUNTBLANK.php b/tests/data/Calculation/Statistical/COUNTBLANK.php
index 35b43167e7..6446a56b0e 100644
--- a/tests/data/Calculation/Statistical/COUNTBLANK.php
+++ b/tests/data/Calculation/Statistical/COUNTBLANK.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         4,
diff --git a/tests/data/Calculation/Statistical/COUNTIF.php b/tests/data/Calculation/Statistical/COUNTIF.php
index 0abf8ae3fa..bdd7f6dfa4 100644
--- a/tests/data/Calculation/Statistical/COUNTIF.php
+++ b/tests/data/Calculation/Statistical/COUNTIF.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2,
diff --git a/tests/data/Calculation/Statistical/COUNTIFS.php b/tests/data/Calculation/Statistical/COUNTIFS.php
index 2f7fc97fef..614d832001 100644
--- a/tests/data/Calculation/Statistical/COUNTIFS.php
+++ b/tests/data/Calculation/Statistical/COUNTIFS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no argument' => [
         'exception',
diff --git a/tests/data/Calculation/Statistical/COVAR.php b/tests/data/Calculation/Statistical/COVAR.php
index d32cc8b3c6..f02bbad8e2 100644
--- a/tests/data/Calculation/Statistical/COVAR.php
+++ b/tests/data/Calculation/Statistical/COVAR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         5.2,
diff --git a/tests/data/Calculation/Statistical/DEVSQ.php b/tests/data/Calculation/Statistical/DEVSQ.php
index 8c1bae2104..4b67e44eaa 100644
--- a/tests/data/Calculation/Statistical/DEVSQ.php
+++ b/tests/data/Calculation/Statistical/DEVSQ.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         48,
diff --git a/tests/data/Calculation/Statistical/EXPONDIST.php b/tests/data/Calculation/Statistical/EXPONDIST.php
index fda340db1e..4afc39226f 100644
--- a/tests/data/Calculation/Statistical/EXPONDIST.php
+++ b/tests/data/Calculation/Statistical/EXPONDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1.353352832366,
diff --git a/tests/data/Calculation/Statistical/ExcelCOUNT.php b/tests/data/Calculation/Statistical/ExcelCOUNT.php
index 0b1c172f12..06863488af 100644
--- a/tests/data/Calculation/Statistical/ExcelCOUNT.php
+++ b/tests/data/Calculation/Statistical/ExcelCOUNT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'passing range do not count bool, null, or text numbers' => [
         3,
diff --git a/tests/data/Calculation/Statistical/FDIST.php b/tests/data/Calculation/Statistical/FDIST.php
index 39be714d99..7ef64c6cb0 100644
--- a/tests/data/Calculation/Statistical/FDIST.php
+++ b/tests/data/Calculation/Statistical/FDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.001223791709,
diff --git a/tests/data/Calculation/Statistical/FISHER.php b/tests/data/Calculation/Statistical/FISHER.php
index faf6442ea5..8b07eb3cd0 100644
--- a/tests/data/Calculation/Statistical/FISHER.php
+++ b/tests/data/Calculation/Statistical/FISHER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         -1.472219489583,
diff --git a/tests/data/Calculation/Statistical/FISHERINV.php b/tests/data/Calculation/Statistical/FISHERINV.php
index d23472b2e5..ae6334aa30 100644
--- a/tests/data/Calculation/Statistical/FISHERINV.php
+++ b/tests/data/Calculation/Statistical/FISHERINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         -0.197375320225,
diff --git a/tests/data/Calculation/Statistical/FORECAST.php b/tests/data/Calculation/Statistical/FORECAST.php
index d14ea0a063..ade2cb8c62 100644
--- a/tests/data/Calculation/Statistical/FORECAST.php
+++ b/tests/data/Calculation/Statistical/FORECAST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         10.607253086419,
diff --git a/tests/data/Calculation/Statistical/GAMMA.php b/tests/data/Calculation/Statistical/GAMMA.php
index 24b83f0450..c9b6b7a70a 100644
--- a/tests/data/Calculation/Statistical/GAMMA.php
+++ b/tests/data/Calculation/Statistical/GAMMA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [1.329340388179, 2.5],
     [0.267865934620, -3.75],
diff --git a/tests/data/Calculation/Statistical/GAMMADIST.php b/tests/data/Calculation/Statistical/GAMMADIST.php
index 2a1bfa14f6..9946053b7e 100644
--- a/tests/data/Calculation/Statistical/GAMMADIST.php
+++ b/tests/data/Calculation/Statistical/GAMMADIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.03263913041829,
diff --git a/tests/data/Calculation/Statistical/GAMMAINV.php b/tests/data/Calculation/Statistical/GAMMAINV.php
index c35c4219ec..5a321a4864 100644
--- a/tests/data/Calculation/Statistical/GAMMAINV.php
+++ b/tests/data/Calculation/Statistical/GAMMAINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         10.0000111914377,
diff --git a/tests/data/Calculation/Statistical/GAMMALN.php b/tests/data/Calculation/Statistical/GAMMALN.php
index 7b43eea8eb..d0dc03e09b 100644
--- a/tests/data/Calculation/Statistical/GAMMALN.php
+++ b/tests/data/Calculation/Statistical/GAMMALN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2.453736570842,
diff --git a/tests/data/Calculation/Statistical/GAUSS.php b/tests/data/Calculation/Statistical/GAUSS.php
index e5dbc17e95..80a1b41587 100644
--- a/tests/data/Calculation/Statistical/GAUSS.php
+++ b/tests/data/Calculation/Statistical/GAUSS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0.4772498680518, 2],
     [-0.4999997133484, -5],
diff --git a/tests/data/Calculation/Statistical/GEOMEAN.php b/tests/data/Calculation/Statistical/GEOMEAN.php
index 1399341123..58337298cf 100644
--- a/tests/data/Calculation/Statistical/GEOMEAN.php
+++ b/tests/data/Calculation/Statistical/GEOMEAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         5.47698696965696,
diff --git a/tests/data/Calculation/Statistical/GROWTH.php b/tests/data/Calculation/Statistical/GROWTH.php
index 25596e301b..cf5d4a62cf 100644
--- a/tests/data/Calculation/Statistical/GROWTH.php
+++ b/tests/data/Calculation/Statistical/GROWTH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/Calculation/Statistical/GnumericCOUNT.php b/tests/data/Calculation/Statistical/GnumericCOUNT.php
index bd2b034732..aadcd23e00 100644
--- a/tests/data/Calculation/Statistical/GnumericCOUNT.php
+++ b/tests/data/Calculation/Statistical/GnumericCOUNT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'range does not count bool, null, text string' => [
         3,
diff --git a/tests/data/Calculation/Statistical/HARMEAN.php b/tests/data/Calculation/Statistical/HARMEAN.php
index 1c34ff3328..e8db95a6f2 100644
--- a/tests/data/Calculation/Statistical/HARMEAN.php
+++ b/tests/data/Calculation/Statistical/HARMEAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         5.028375962062,
diff --git a/tests/data/Calculation/Statistical/HYPGEOMDIST.php b/tests/data/Calculation/Statistical/HYPGEOMDIST.php
index aae0a05fd7..a56084bd39 100644
--- a/tests/data/Calculation/Statistical/HYPGEOMDIST.php
+++ b/tests/data/Calculation/Statistical/HYPGEOMDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.3632610939112,
diff --git a/tests/data/Calculation/Statistical/INTERCEPT.php b/tests/data/Calculation/Statistical/INTERCEPT.php
index f4f25a28da..b4fc755092 100644
--- a/tests/data/Calculation/Statistical/INTERCEPT.php
+++ b/tests/data/Calculation/Statistical/INTERCEPT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         25.0,
diff --git a/tests/data/Calculation/Statistical/KURT.php b/tests/data/Calculation/Statistical/KURT.php
index bc3a009c78..8036ec09f2 100644
--- a/tests/data/Calculation/Statistical/KURT.php
+++ b/tests/data/Calculation/Statistical/KURT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return[
     [
         -0.1517996372084,
diff --git a/tests/data/Calculation/Statistical/LARGE.php b/tests/data/Calculation/Statistical/LARGE.php
index 3a6adcba95..60a3dc229e 100644
--- a/tests/data/Calculation/Statistical/LARGE.php
+++ b/tests/data/Calculation/Statistical/LARGE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         5,
diff --git a/tests/data/Calculation/Statistical/LINEST.php b/tests/data/Calculation/Statistical/LINEST.php
index 429c6a766d..ceae99db44 100644
--- a/tests/data/Calculation/Statistical/LINEST.php
+++ b/tests/data/Calculation/Statistical/LINEST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/Statistical/LOGEST.php b/tests/data/Calculation/Statistical/LOGEST.php
index bba7487b97..a15dbbf8a9 100644
--- a/tests/data/Calculation/Statistical/LOGEST.php
+++ b/tests/data/Calculation/Statistical/LOGEST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [1.000174230092, 1.0],
diff --git a/tests/data/Calculation/Statistical/LOGINV.php b/tests/data/Calculation/Statistical/LOGINV.php
index 43f4615539..1442caebe7 100644
--- a/tests/data/Calculation/Statistical/LOGINV.php
+++ b/tests/data/Calculation/Statistical/LOGINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         4.000025209777,
diff --git a/tests/data/Calculation/Statistical/LOGNORMDIST.php b/tests/data/Calculation/Statistical/LOGNORMDIST.php
index cc1dc87129..eaf9fbe6f8 100644
--- a/tests/data/Calculation/Statistical/LOGNORMDIST.php
+++ b/tests/data/Calculation/Statistical/LOGNORMDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return[
     [0.0390835557068, 4, 3.5, 1.2],
     [0.066417114799, 12, 10, 5],
diff --git a/tests/data/Calculation/Statistical/LOGNORMDIST2.php b/tests/data/Calculation/Statistical/LOGNORMDIST2.php
index 4b709f8b4e..96a966b33c 100644
--- a/tests/data/Calculation/Statistical/LOGNORMDIST2.php
+++ b/tests/data/Calculation/Statistical/LOGNORMDIST2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return[
     [0.0390835557068, 4, 3.5, 1.2, true],
     [0.0176175966818, 4, 3.5, 1.2, false],
diff --git a/tests/data/Calculation/Statistical/MAX.php b/tests/data/Calculation/Statistical/MAX.php
index fc1f8a0e1a..b9361b6a55 100644
--- a/tests/data/Calculation/Statistical/MAX.php
+++ b/tests/data/Calculation/Statistical/MAX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         27,
diff --git a/tests/data/Calculation/Statistical/MAXA.php b/tests/data/Calculation/Statistical/MAXA.php
index 992140e79b..88e01e9d81 100644
--- a/tests/data/Calculation/Statistical/MAXA.php
+++ b/tests/data/Calculation/Statistical/MAXA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         27,
diff --git a/tests/data/Calculation/Statistical/MAXIFS.php b/tests/data/Calculation/Statistical/MAXIFS.php
index cafdff0225..a1b3fa0e4a 100644
--- a/tests/data/Calculation/Statistical/MAXIFS.php
+++ b/tests/data/Calculation/Statistical/MAXIFS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no argument' => [
         'exception',
diff --git a/tests/data/Calculation/Statistical/MEDIAN.php b/tests/data/Calculation/Statistical/MEDIAN.php
index bde86d480e..3eca4feb82 100644
--- a/tests/data/Calculation/Statistical/MEDIAN.php
+++ b/tests/data/Calculation/Statistical/MEDIAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         8.0,
diff --git a/tests/data/Calculation/Statistical/MIN.php b/tests/data/Calculation/Statistical/MIN.php
index f53fc6e5b9..3ac8898f9a 100644
--- a/tests/data/Calculation/Statistical/MIN.php
+++ b/tests/data/Calculation/Statistical/MIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2,
diff --git a/tests/data/Calculation/Statistical/MINA.php b/tests/data/Calculation/Statistical/MINA.php
index 5722eb5622..b4aa51b433 100644
--- a/tests/data/Calculation/Statistical/MINA.php
+++ b/tests/data/Calculation/Statistical/MINA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2,
diff --git a/tests/data/Calculation/Statistical/MINIFS.php b/tests/data/Calculation/Statistical/MINIFS.php
index 00bd56b0c6..f5d11c131e 100644
--- a/tests/data/Calculation/Statistical/MINIFS.php
+++ b/tests/data/Calculation/Statistical/MINIFS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no argument' => [
         'exception',
diff --git a/tests/data/Calculation/Statistical/MODE.php b/tests/data/Calculation/Statistical/MODE.php
index 7d27b33e5e..a2d6eb9716 100644
--- a/tests/data/Calculation/Statistical/MODE.php
+++ b/tests/data/Calculation/Statistical/MODE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [4.1, '{5.6,4.1,4.1,3,2,4.1}'], // Calculated value was #N/A
     [4.1, '5.6,4.1,4.1,3,2,4.1'],
diff --git a/tests/data/Calculation/Statistical/NEGBINOMDIST.php b/tests/data/Calculation/Statistical/NEGBINOMDIST.php
index fd983cc15f..04f572c0fc 100644
--- a/tests/data/Calculation/Statistical/NEGBINOMDIST.php
+++ b/tests/data/Calculation/Statistical/NEGBINOMDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.05504866037517786,
diff --git a/tests/data/Calculation/Statistical/NORMDIST.php b/tests/data/Calculation/Statistical/NORMDIST.php
index 7ff3f8d8d3..60203b484a 100644
--- a/tests/data/Calculation/Statistical/NORMDIST.php
+++ b/tests/data/Calculation/Statistical/NORMDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0.9087887802741, 42, 40, 1.5, true],
     [0.109340049784, 42, 40, 1.5, false],
diff --git a/tests/data/Calculation/Statistical/NORMINV.php b/tests/data/Calculation/Statistical/NORMINV.php
index db4bac2bd0..9acd94d210 100644
--- a/tests/data/Calculation/Statistical/NORMINV.php
+++ b/tests/data/Calculation/Statistical/NORMINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [42.000002008416, 0.908789, 40, 1.5],
     [5.50669420572, 0.6, 5, 2],
diff --git a/tests/data/Calculation/Statistical/NORMSDIST.php b/tests/data/Calculation/Statistical/NORMSDIST.php
index aeb5405973..da94962cbc 100644
--- a/tests/data/Calculation/Statistical/NORMSDIST.php
+++ b/tests/data/Calculation/Statistical/NORMSDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0.908788780274, 1.333333333333],
     [0.788144601416, 0.8],
diff --git a/tests/data/Calculation/Statistical/NORMSDIST2.php b/tests/data/Calculation/Statistical/NORMSDIST2.php
index 0f7c06d862..27accdc15e 100644
--- a/tests/data/Calculation/Statistical/NORMSDIST2.php
+++ b/tests/data/Calculation/Statistical/NORMSDIST2.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [0.908788780274, 1.333333333333, true],
     [0.164010074676, 1.333333333333, false],
diff --git a/tests/data/Calculation/Statistical/NORMSINV.php b/tests/data/Calculation/Statistical/NORMSINV.php
index 206bd16330..739003a428 100644
--- a/tests/data/Calculation/Statistical/NORMSINV.php
+++ b/tests/data/Calculation/Statistical/NORMSINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [1.33333467227723, 0.908789],
     [-0.67448975022342, 0.25],
diff --git a/tests/data/Calculation/Statistical/OpenOfficeCOUNT.php b/tests/data/Calculation/Statistical/OpenOfficeCOUNT.php
index 726e12a5b5..82faafb242 100644
--- a/tests/data/Calculation/Statistical/OpenOfficeCOUNT.php
+++ b/tests/data/Calculation/Statistical/OpenOfficeCOUNT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'passing range count bool but not null nor text numbers' => [
         5,
diff --git a/tests/data/Calculation/Statistical/PERCENTILE.php b/tests/data/Calculation/Statistical/PERCENTILE.php
index 890399c531..4cf5173b67 100644
--- a/tests/data/Calculation/Statistical/PERCENTILE.php
+++ b/tests/data/Calculation/Statistical/PERCENTILE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1.9,
diff --git a/tests/data/Calculation/Statistical/PERCENTRANK.php b/tests/data/Calculation/Statistical/PERCENTRANK.php
index 3787a7ac15..fc8840f7af 100644
--- a/tests/data/Calculation/Statistical/PERCENTRANK.php
+++ b/tests/data/Calculation/Statistical/PERCENTRANK.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.667,
diff --git a/tests/data/Calculation/Statistical/PERMUT.php b/tests/data/Calculation/Statistical/PERMUT.php
index 80b3a93de4..50fe816f7d 100644
--- a/tests/data/Calculation/Statistical/PERMUT.php
+++ b/tests/data/Calculation/Statistical/PERMUT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         5,
diff --git a/tests/data/Calculation/Statistical/PERMUTATIONA.php b/tests/data/Calculation/Statistical/PERMUTATIONA.php
index 701f5eac48..fdaee63aff 100644
--- a/tests/data/Calculation/Statistical/PERMUTATIONA.php
+++ b/tests/data/Calculation/Statistical/PERMUTATIONA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         5,
diff --git a/tests/data/Calculation/Statistical/POISSON.php b/tests/data/Calculation/Statistical/POISSON.php
index 7c839ac761..4ec9474dbf 100644
--- a/tests/data/Calculation/Statistical/POISSON.php
+++ b/tests/data/Calculation/Statistical/POISSON.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.12465201948308113,
diff --git a/tests/data/Calculation/Statistical/QUARTILE.php b/tests/data/Calculation/Statistical/QUARTILE.php
index 33f0ea8b8e..70810fd8c0 100644
--- a/tests/data/Calculation/Statistical/QUARTILE.php
+++ b/tests/data/Calculation/Statistical/QUARTILE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3.5,
diff --git a/tests/data/Calculation/Statistical/RANK.php b/tests/data/Calculation/Statistical/RANK.php
index 0ca23581d8..ccd7ca2196 100644
--- a/tests/data/Calculation/Statistical/RANK.php
+++ b/tests/data/Calculation/Statistical/RANK.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         2,
diff --git a/tests/data/Calculation/Statistical/RSQ.php b/tests/data/Calculation/Statistical/RSQ.php
index f414ef555b..3565f58a57 100644
--- a/tests/data/Calculation/Statistical/RSQ.php
+++ b/tests/data/Calculation/Statistical/RSQ.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.057950191571,
diff --git a/tests/data/Calculation/Statistical/SKEW.php b/tests/data/Calculation/Statistical/SKEW.php
index 9384613f25..afbb1ee83e 100644
--- a/tests/data/Calculation/Statistical/SKEW.php
+++ b/tests/data/Calculation/Statistical/SKEW.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.359543071407,
diff --git a/tests/data/Calculation/Statistical/SLOPE.php b/tests/data/Calculation/Statistical/SLOPE.php
index a7730b9cd8..c8d4a827b2 100644
--- a/tests/data/Calculation/Statistical/SLOPE.php
+++ b/tests/data/Calculation/Statistical/SLOPE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Shared\Date;
 
 return [
diff --git a/tests/data/Calculation/Statistical/SMALL.php b/tests/data/Calculation/Statistical/SMALL.php
index d339566020..7efaf8a9bd 100644
--- a/tests/data/Calculation/Statistical/SMALL.php
+++ b/tests/data/Calculation/Statistical/SMALL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3,
diff --git a/tests/data/Calculation/Statistical/STANDARDIZE.php b/tests/data/Calculation/Statistical/STANDARDIZE.php
index c2e4c9f786..605f070996 100644
--- a/tests/data/Calculation/Statistical/STANDARDIZE.php
+++ b/tests/data/Calculation/Statistical/STANDARDIZE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [1.333333333333, 42, 40, 1.5],
     [0.25, 5.5, 5, 2],
diff --git a/tests/data/Calculation/Statistical/STDEV.php b/tests/data/Calculation/Statistical/STDEV.php
index 30d9dc3b81..03a3018130 100644
--- a/tests/data/Calculation/Statistical/STDEV.php
+++ b/tests/data/Calculation/Statistical/STDEV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         27.463915719843,
diff --git a/tests/data/Calculation/Statistical/STDEVA.php b/tests/data/Calculation/Statistical/STDEVA.php
index 13cecc6171..cc3b888081 100644
--- a/tests/data/Calculation/Statistical/STDEVA.php
+++ b/tests/data/Calculation/Statistical/STDEVA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         27.463915719843,
diff --git a/tests/data/Calculation/Statistical/STDEVA_ODS.php b/tests/data/Calculation/Statistical/STDEVA_ODS.php
index 559798e463..f0fe11b319 100644
--- a/tests/data/Calculation/Statistical/STDEVA_ODS.php
+++ b/tests/data/Calculation/Statistical/STDEVA_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         27.463915719843,
diff --git a/tests/data/Calculation/Statistical/STDEVP.php b/tests/data/Calculation/Statistical/STDEVP.php
index 443a993c10..964dc3d8df 100644
--- a/tests/data/Calculation/Statistical/STDEVP.php
+++ b/tests/data/Calculation/Statistical/STDEVP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         26.0545581424825,
diff --git a/tests/data/Calculation/Statistical/STDEVPA.php b/tests/data/Calculation/Statistical/STDEVPA.php
index 3ca865a3d5..536763ae40 100644
--- a/tests/data/Calculation/Statistical/STDEVPA.php
+++ b/tests/data/Calculation/Statistical/STDEVPA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         26.0545581424825,
diff --git a/tests/data/Calculation/Statistical/STDEVPA_ODS.php b/tests/data/Calculation/Statistical/STDEVPA_ODS.php
index 3ca865a3d5..536763ae40 100644
--- a/tests/data/Calculation/Statistical/STDEVPA_ODS.php
+++ b/tests/data/Calculation/Statistical/STDEVPA_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         26.0545581424825,
diff --git a/tests/data/Calculation/Statistical/STDEVP_ODS.php b/tests/data/Calculation/Statistical/STDEVP_ODS.php
index 131a239772..e672b29868 100644
--- a/tests/data/Calculation/Statistical/STDEVP_ODS.php
+++ b/tests/data/Calculation/Statistical/STDEVP_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         26.0545581424825,
diff --git a/tests/data/Calculation/Statistical/STDEV_ODS.php b/tests/data/Calculation/Statistical/STDEV_ODS.php
index 7129ed0b7b..481f4f6d46 100644
--- a/tests/data/Calculation/Statistical/STDEV_ODS.php
+++ b/tests/data/Calculation/Statistical/STDEV_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         27.463915719843,
diff --git a/tests/data/Calculation/Statistical/STEYX.php b/tests/data/Calculation/Statistical/STEYX.php
index a87ff59224..80c6587c6e 100644
--- a/tests/data/Calculation/Statistical/STEYX.php
+++ b/tests/data/Calculation/Statistical/STEYX.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3.305718950210,
diff --git a/tests/data/Calculation/Statistical/TDIST.php b/tests/data/Calculation/Statistical/TDIST.php
index 7bf046fc40..298675a453 100644
--- a/tests/data/Calculation/Statistical/TDIST.php
+++ b/tests/data/Calculation/Statistical/TDIST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.027322464988,
diff --git a/tests/data/Calculation/Statistical/TINV.php b/tests/data/Calculation/Statistical/TINV.php
index e288bcd06f..ec602c7fc9 100644
--- a/tests/data/Calculation/Statistical/TINV.php
+++ b/tests/data/Calculation/Statistical/TINV.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1.960041187127,
diff --git a/tests/data/Calculation/Statistical/TREND.php b/tests/data/Calculation/Statistical/TREND.php
index 418367b2e5..adac7afe69 100644
--- a/tests/data/Calculation/Statistical/TREND.php
+++ b/tests/data/Calculation/Statistical/TREND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/Calculation/Statistical/TRIMMEAN.php b/tests/data/Calculation/Statistical/TRIMMEAN.php
index 5ec07a04f2..a009e078d7 100644
--- a/tests/data/Calculation/Statistical/TRIMMEAN.php
+++ b/tests/data/Calculation/Statistical/TRIMMEAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3.777777777778,
diff --git a/tests/data/Calculation/Statistical/VAR.php b/tests/data/Calculation/Statistical/VAR.php
index baedd48cdf..92ab96e600 100644
--- a/tests/data/Calculation/Statistical/VAR.php
+++ b/tests/data/Calculation/Statistical/VAR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         754.266666666667,
diff --git a/tests/data/Calculation/Statistical/VARA.php b/tests/data/Calculation/Statistical/VARA.php
index 444a789eaf..5dd68c7745 100644
--- a/tests/data/Calculation/Statistical/VARA.php
+++ b/tests/data/Calculation/Statistical/VARA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         754.266666666667,
diff --git a/tests/data/Calculation/Statistical/VARA_ODS.php b/tests/data/Calculation/Statistical/VARA_ODS.php
index 444a789eaf..5dd68c7745 100644
--- a/tests/data/Calculation/Statistical/VARA_ODS.php
+++ b/tests/data/Calculation/Statistical/VARA_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         754.266666666667,
diff --git a/tests/data/Calculation/Statistical/VARP.php b/tests/data/Calculation/Statistical/VARP.php
index 519de42bf3..9845125d7e 100644
--- a/tests/data/Calculation/Statistical/VARP.php
+++ b/tests/data/Calculation/Statistical/VARP.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         678.84,
diff --git a/tests/data/Calculation/Statistical/VARPA.php b/tests/data/Calculation/Statistical/VARPA.php
index a78a01793a..52a1d49366 100644
--- a/tests/data/Calculation/Statistical/VARPA.php
+++ b/tests/data/Calculation/Statistical/VARPA.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         678.84,
diff --git a/tests/data/Calculation/Statistical/VARPA_ODS.php b/tests/data/Calculation/Statistical/VARPA_ODS.php
index a78a01793a..52a1d49366 100644
--- a/tests/data/Calculation/Statistical/VARPA_ODS.php
+++ b/tests/data/Calculation/Statistical/VARPA_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         678.84,
diff --git a/tests/data/Calculation/Statistical/VARP_ODS.php b/tests/data/Calculation/Statistical/VARP_ODS.php
index a78a01793a..52a1d49366 100644
--- a/tests/data/Calculation/Statistical/VARP_ODS.php
+++ b/tests/data/Calculation/Statistical/VARP_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         678.84,
diff --git a/tests/data/Calculation/Statistical/VAR_ODS.php b/tests/data/Calculation/Statistical/VAR_ODS.php
index 444a789eaf..5dd68c7745 100644
--- a/tests/data/Calculation/Statistical/VAR_ODS.php
+++ b/tests/data/Calculation/Statistical/VAR_ODS.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         754.266666666667,
diff --git a/tests/data/Calculation/Statistical/WEIBULL.php b/tests/data/Calculation/Statistical/WEIBULL.php
index 87f47ad28c..002f260320 100644
--- a/tests/data/Calculation/Statistical/WEIBULL.php
+++ b/tests/data/Calculation/Statistical/WEIBULL.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.929581390070,
diff --git a/tests/data/Calculation/Statistical/ZTEST.php b/tests/data/Calculation/Statistical/ZTEST.php
index 9de2a8370b..235048d116 100644
--- a/tests/data/Calculation/Statistical/ZTEST.php
+++ b/tests/data/Calculation/Statistical/ZTEST.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0.090574196851,
diff --git a/tests/data/Calculation/TextData/ARRAYTOTEXT.php b/tests/data/Calculation/TextData/ARRAYTOTEXT.php
index 4bef2823d2..f5dd6cb140 100644
--- a/tests/data/Calculation/TextData/ARRAYTOTEXT.php
+++ b/tests/data/Calculation/TextData/ARRAYTOTEXT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         "1, 2, 3, a, b, c, TRUE, FALSE, #DIV/0!, 44774, 1, 44777, 12345.6789, -2.4, Hello\nWorld",
diff --git a/tests/data/Calculation/TextData/CHAR.php b/tests/data/Calculation/TextData/CHAR.php
index f02437b7d0..400edd50dd 100644
--- a/tests/data/Calculation/TextData/CHAR.php
+++ b/tests/data/Calculation/TextData/CHAR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#VALUE!',
diff --git a/tests/data/Calculation/TextData/CLEAN.php b/tests/data/Calculation/TextData/CLEAN.php
index ad668271a3..255a8222fb 100644
--- a/tests/data/Calculation/TextData/CLEAN.php
+++ b/tests/data/Calculation/TextData/CLEAN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'HELLO      ',
diff --git a/tests/data/Calculation/TextData/CODE.php b/tests/data/Calculation/TextData/CODE.php
index 8ab927263e..62bd213b2d 100644
--- a/tests/data/Calculation/TextData/CODE.php
+++ b/tests/data/Calculation/TextData/CODE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#VALUE!',
diff --git a/tests/data/Calculation/TextData/CONCATENATE.php b/tests/data/Calculation/TextData/CONCATENATE.php
index b29843f7f3..c37c2ffcdb 100644
--- a/tests/data/Calculation/TextData/CONCATENATE.php
+++ b/tests/data/Calculation/TextData/CONCATENATE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
 
 return [
diff --git a/tests/data/Calculation/TextData/DOLLAR.php b/tests/data/Calculation/TextData/DOLLAR.php
index 78fcc1b52e..d20e173d1f 100644
--- a/tests/data/Calculation/TextData/DOLLAR.php
+++ b/tests/data/Calculation/TextData/DOLLAR.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '$123.46',
diff --git a/tests/data/Calculation/TextData/EXACT.php b/tests/data/Calculation/TextData/EXACT.php
index f392b0b055..aa54f6f2f1 100644
--- a/tests/data/Calculation/TextData/EXACT.php
+++ b/tests/data/Calculation/TextData/EXACT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         true,
diff --git a/tests/data/Calculation/TextData/FIND.php b/tests/data/Calculation/TextData/FIND.php
index 1ae6d730ea..027f62d2d2 100644
--- a/tests/data/Calculation/TextData/FIND.php
+++ b/tests/data/Calculation/TextData/FIND.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3,
diff --git a/tests/data/Calculation/TextData/FIXED.php b/tests/data/Calculation/TextData/FIXED.php
index 29734404cd..e13b8110e2 100644
--- a/tests/data/Calculation/TextData/FIXED.php
+++ b/tests/data/Calculation/TextData/FIXED.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '123,456.79',
diff --git a/tests/data/Calculation/TextData/LEFT.php b/tests/data/Calculation/TextData/LEFT.php
index 17d3fcf7a5..1bf71c99d0 100644
--- a/tests/data/Calculation/TextData/LEFT.php
+++ b/tests/data/Calculation/TextData/LEFT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '',
diff --git a/tests/data/Calculation/TextData/LEN.php b/tests/data/Calculation/TextData/LEN.php
index babf3535a6..e07be820cf 100644
--- a/tests/data/Calculation/TextData/LEN.php
+++ b/tests/data/Calculation/TextData/LEN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         0,
diff --git a/tests/data/Calculation/TextData/LOWER.php b/tests/data/Calculation/TextData/LOWER.php
index 23825546d2..39c286f8b2 100644
--- a/tests/data/Calculation/TextData/LOWER.php
+++ b/tests/data/Calculation/TextData/LOWER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'abcdefghi',
diff --git a/tests/data/Calculation/TextData/MID.php b/tests/data/Calculation/TextData/MID.php
index 45e0ceab9b..9379b9471e 100644
--- a/tests/data/Calculation/TextData/MID.php
+++ b/tests/data/Calculation/TextData/MID.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '',
diff --git a/tests/data/Calculation/TextData/NUMBERVALUE.php b/tests/data/Calculation/TextData/NUMBERVALUE.php
index 6131317426..5e979763f5 100644
--- a/tests/data/Calculation/TextData/NUMBERVALUE.php
+++ b/tests/data/Calculation/TextData/NUMBERVALUE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1234567.89,
diff --git a/tests/data/Calculation/TextData/OpenOffice.php b/tests/data/Calculation/TextData/OpenOffice.php
index fc79d5f11c..5c1c4a0356 100644
--- a/tests/data/Calculation/TextData/OpenOffice.php
+++ b/tests/data/Calculation/TextData/OpenOffice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'OO allows CHAR(0)' => ["\x00", '=CHAR(0)'],
     'OO treats CODE(bool) as 0/1' => ['48', '=CODE(FALSE)'],
diff --git a/tests/data/Calculation/TextData/PROPER.php b/tests/data/Calculation/TextData/PROPER.php
index e9a5d4ceb6..6798151c07 100644
--- a/tests/data/Calculation/TextData/PROPER.php
+++ b/tests/data/Calculation/TextData/PROPER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'Mark Baker',
diff --git a/tests/data/Calculation/TextData/REPLACE.php b/tests/data/Calculation/TextData/REPLACE.php
index 2268bf48d2..d36e7beb6c 100644
--- a/tests/data/Calculation/TextData/REPLACE.php
+++ b/tests/data/Calculation/TextData/REPLACE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'QWDFGYUIOP',
diff --git a/tests/data/Calculation/TextData/REPT.php b/tests/data/Calculation/TextData/REPT.php
index 172d8faeec..f3369c5060 100644
--- a/tests/data/Calculation/TextData/REPT.php
+++ b/tests/data/Calculation/TextData/REPT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'no arguments' => ['exception'],
     'one argument' => ['exception', 'ABC'],
diff --git a/tests/data/Calculation/TextData/RIGHT.php b/tests/data/Calculation/TextData/RIGHT.php
index 77ea64bf71..922a3591e3 100644
--- a/tests/data/Calculation/TextData/RIGHT.php
+++ b/tests/data/Calculation/TextData/RIGHT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '',
diff --git a/tests/data/Calculation/TextData/SEARCH.php b/tests/data/Calculation/TextData/SEARCH.php
index 335a7f12a8..34600d3091 100644
--- a/tests/data/Calculation/TextData/SEARCH.php
+++ b/tests/data/Calculation/TextData/SEARCH.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3,
diff --git a/tests/data/Calculation/TextData/SUBSTITUTE.php b/tests/data/Calculation/TextData/SUBSTITUTE.php
index baf1c87b2f..8d9b90a0a3 100644
--- a/tests/data/Calculation/TextData/SUBSTITUTE.php
+++ b/tests/data/Calculation/TextData/SUBSTITUTE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'QWDFGYUIOP',
diff --git a/tests/data/Calculation/TextData/T.php b/tests/data/Calculation/TextData/T.php
index 802b936fa7..7fab8a1e9f 100644
--- a/tests/data/Calculation/TextData/T.php
+++ b/tests/data/Calculation/TextData/T.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '',
diff --git a/tests/data/Calculation/TextData/TEXT.php b/tests/data/Calculation/TextData/TEXT.php
index 5bf87a87df..19032d0062 100644
--- a/tests/data/Calculation/TextData/TEXT.php
+++ b/tests/data/Calculation/TextData/TEXT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '$123.46',
diff --git a/tests/data/Calculation/TextData/TEXTAFTER.php b/tests/data/Calculation/TextData/TEXTAFTER.php
index c0e3e3d51f..ba22ce55d7 100644
--- a/tests/data/Calculation/TextData/TEXTAFTER.php
+++ b/tests/data/Calculation/TextData/TEXTAFTER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/TextData/TEXTBEFORE.php b/tests/data/Calculation/TextData/TEXTBEFORE.php
index a79d37b0fd..7987908da3 100644
--- a/tests/data/Calculation/TextData/TEXTBEFORE.php
+++ b/tests/data/Calculation/TextData/TEXTBEFORE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/TextData/TEXTJOIN.php b/tests/data/Calculation/TextData/TEXTJOIN.php
index 392f7e4f27..3908abb875 100644
--- a/tests/data/Calculation/TextData/TEXTJOIN.php
+++ b/tests/data/Calculation/TextData/TEXTJOIN.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
 
 return [
diff --git a/tests/data/Calculation/TextData/TEXTSPLIT.php b/tests/data/Calculation/TextData/TEXTSPLIT.php
index a10b26f6e8..118685a709 100644
--- a/tests/data/Calculation/TextData/TEXTSPLIT.php
+++ b/tests/data/Calculation/TextData/TEXTSPLIT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 
 return [
diff --git a/tests/data/Calculation/TextData/TRIM.php b/tests/data/Calculation/TextData/TRIM.php
index 882dc824d1..42c3b39656 100644
--- a/tests/data/Calculation/TextData/TRIM.php
+++ b/tests/data/Calculation/TextData/TRIM.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'HELLO',
diff --git a/tests/data/Calculation/TextData/UPPER.php b/tests/data/Calculation/TextData/UPPER.php
index 21b04ae46a..5810fbe321 100644
--- a/tests/data/Calculation/TextData/UPPER.php
+++ b/tests/data/Calculation/TextData/UPPER.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'ABCDEFGHI',
diff --git a/tests/data/Calculation/TextData/VALUE.php b/tests/data/Calculation/TextData/VALUE.php
index 1a007005ec..c558881076 100644
--- a/tests/data/Calculation/TextData/VALUE.php
+++ b/tests/data/Calculation/TextData/VALUE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '1000',
diff --git a/tests/data/Calculation/TextData/VALUETOTEXT.php b/tests/data/Calculation/TextData/VALUETOTEXT.php
index 13df19ab1c..b3871a43ae 100644
--- a/tests/data/Calculation/TextData/VALUETOTEXT.php
+++ b/tests/data/Calculation/TextData/VALUETOTEXT.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\RichText\RichText;
 
 $richText1 = new RichText();
diff --git a/tests/data/Calculation/Translations.php b/tests/data/Calculation/Translations.php
index 0965bac1ca..b0849ff274 100644
--- a/tests/data/Calculation/Translations.php
+++ b/tests/data/Calculation/Translations.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '=DAGEN360(DATUM(2010;2;5);DATUM(2010;12;31);WAAR)',
diff --git a/tests/data/Calculation/Web/URLENCODE.php b/tests/data/Calculation/Web/URLENCODE.php
index 3a227ae5ce..fcc9dc0346 100644
--- a/tests/data/Calculation/Web/URLENCODE.php
+++ b/tests/data/Calculation/Web/URLENCODE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'http%3A%2F%2Fcontoso.sharepoint.com%2Fteams%2FFinance%2FDocuments%2FApril%20Reports%2FProfit%20and%20Loss%20Statement.xlsx',
diff --git a/tests/data/Calculation/Web/WEBSERVICE.php b/tests/data/Calculation/Web/WEBSERVICE.php
index 418761411c..f2c6f9008f 100644
--- a/tests/data/Calculation/Web/WEBSERVICE.php
+++ b/tests/data/Calculation/Web/WEBSERVICE.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '#VALUE!',
diff --git a/tests/data/CalculationBinaryComparisonOperation.php b/tests/data/CalculationBinaryComparisonOperation.php
index a8c8e4ece2..2826b9b755 100644
--- a/tests/data/CalculationBinaryComparisonOperation.php
+++ b/tests/data/CalculationBinaryComparisonOperation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 //  formula, expectedResultExcel, expectedResultOpenOffice
 
 return [
diff --git a/tests/data/Cell/A1ConversionToR1C1Absolute.php b/tests/data/Cell/A1ConversionToR1C1Absolute.php
index 171672bbff..14e6ec6111 100644
--- a/tests/data/Cell/A1ConversionToR1C1Absolute.php
+++ b/tests/data/Cell/A1ConversionToR1C1Absolute.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['R1C1', 'A1'],
     ['R1C1', '$A$1'],
diff --git a/tests/data/Cell/A1ConversionToR1C1Exception.php b/tests/data/Cell/A1ConversionToR1C1Exception.php
index 7dd4a68ede..f8b0ee9bb3 100644
--- a/tests/data/Cell/A1ConversionToR1C1Exception.php
+++ b/tests/data/Cell/A1ConversionToR1C1Exception.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['A11Y'],
 ];
diff --git a/tests/data/Cell/A1ConversionToR1C1Relative.php b/tests/data/Cell/A1ConversionToR1C1Relative.php
index dd9b23918f..8824c49166 100644
--- a/tests/data/Cell/A1ConversionToR1C1Relative.php
+++ b/tests/data/Cell/A1ConversionToR1C1Relative.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['R[2]C[2]', 'O18', 16, 13],
     ['R18C15', '$O$18', 16, 13],
diff --git a/tests/data/Cell/ConvertFormulaToA1FromR1C1Absolute.php b/tests/data/Cell/ConvertFormulaToA1FromR1C1Absolute.php
index 5624c0c96c..d4d0f28543 100644
--- a/tests/data/Cell/ConvertFormulaToA1FromR1C1Absolute.php
+++ b/tests/data/Cell/ConvertFormulaToA1FromR1C1Absolute.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'Basic addition' => ['=D3+F7+G4+C6+5', '=R3C4+R7C6+R4C7+R6C3+5'],
     'Basic subtraction' => ['=D3-F7-G4-C6-5', '=R3C4-R7C6-R4C7-R6C3-5'],
diff --git a/tests/data/Cell/ConvertFormulaToA1FromR1C1Relative.php b/tests/data/Cell/ConvertFormulaToA1FromR1C1Relative.php
index d6df418cda..84e11af3b1 100644
--- a/tests/data/Cell/ConvertFormulaToA1FromR1C1Relative.php
+++ b/tests/data/Cell/ConvertFormulaToA1FromR1C1Relative.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'Basic addition' => ['=D3+F7+G4+C6+5', '=R[-2]C[-1]+R[2]C[1]+R[-1]C[2]+R[1]C[-2]+5', 5, 5],
     'Basic subtraction' => ['=D3-F7-G4-C6-5', '=R[-2]C[-1]-R[2]C[1]-R[-1]C[2]-R[1]C[-2]-5', 5, 5],
diff --git a/tests/data/Cell/ConvertFormulaToA1FromSpreadsheetXml.php b/tests/data/Cell/ConvertFormulaToA1FromSpreadsheetXml.php
index d350c07b30..915d1a4689 100644
--- a/tests/data/Cell/ConvertFormulaToA1FromSpreadsheetXml.php
+++ b/tests/data/Cell/ConvertFormulaToA1FromSpreadsheetXml.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'Basic addition' => ['=D3+F7+G4+C6+5', 'of:=[.D3]+[.F7]+[.G4]+[.C6]+5'],
     'Basic subtraction' => ['=D3-F7-G4-C6-5', 'of:=[.D3]-[.F7]-[.G4]-[.C6]-5'],
diff --git a/tests/data/Cell/DefaultValueBinder.php b/tests/data/Cell/DefaultValueBinder.php
index f5dafc7bc1..b9f3d51e11 100644
--- a/tests/data/Cell/DefaultValueBinder.php
+++ b/tests/data/Cell/DefaultValueBinder.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'null',
diff --git a/tests/data/Cell/IndexesFromString.php b/tests/data/Cell/IndexesFromString.php
index 0a79e47f47..4b223a5a3d 100644
--- a/tests/data/Cell/IndexesFromString.php
+++ b/tests/data/Cell/IndexesFromString.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/Cell/R1C1ConversionToA1Absolute.php b/tests/data/Cell/R1C1ConversionToA1Absolute.php
index 8828934ea1..ff619b7978 100644
--- a/tests/data/Cell/R1C1ConversionToA1Absolute.php
+++ b/tests/data/Cell/R1C1ConversionToA1Absolute.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['A1', 'R1C1'],
     ['B2', 'R2C2'],
diff --git a/tests/data/Cell/R1C1ConversionToA1Exception.php b/tests/data/Cell/R1C1ConversionToA1Exception.php
index fa27fbe95a..eb3aa83675 100644
--- a/tests/data/Cell/R1C1ConversionToA1Exception.php
+++ b/tests/data/Cell/R1C1ConversionToA1Exception.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['RICE'],
     ['R[-1]C'],
diff --git a/tests/data/Cell/R1C1ConversionToA1Relative.php b/tests/data/Cell/R1C1ConversionToA1Relative.php
index 9e7d97ba39..5a74970cb7 100644
--- a/tests/data/Cell/R1C1ConversionToA1Relative.php
+++ b/tests/data/Cell/R1C1ConversionToA1Relative.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     ['C3', 'R[2]C[2]'],
     ['O18', 'R[2]C[2]', 16, 13],
diff --git a/tests/data/Cell/SetValueExplicit.php b/tests/data/Cell/SetValueExplicit.php
index 13a1e33a53..2bb7b01b46 100644
--- a/tests/data/Cell/SetValueExplicit.php
+++ b/tests/data/Cell/SetValueExplicit.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Calculation\Information\ExcelError;
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
 
diff --git a/tests/data/Cell/SetValueExplicitException.php b/tests/data/Cell/SetValueExplicitException.php
index a05704f025..6b1508190f 100644
--- a/tests/data/Cell/SetValueExplicitException.php
+++ b/tests/data/Cell/SetValueExplicitException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Cell\DataType;
 
 return [
diff --git a/tests/data/CellAbsoluteCoordinate.php b/tests/data/CellAbsoluteCoordinate.php
index 86487585c2..a8e304125c 100644
--- a/tests/data/CellAbsoluteCoordinate.php
+++ b/tests/data/CellAbsoluteCoordinate.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '$A$1',
diff --git a/tests/data/CellAbsoluteReference.php b/tests/data/CellAbsoluteReference.php
index 71dac54547..d628d800f6 100644
--- a/tests/data/CellAbsoluteReference.php
+++ b/tests/data/CellAbsoluteReference.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '$A$1',
diff --git a/tests/data/CellBuildRange.php b/tests/data/CellBuildRange.php
index 1eb0ef345c..60496a5d60 100644
--- a/tests/data/CellBuildRange.php
+++ b/tests/data/CellBuildRange.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'B4:E9',
diff --git a/tests/data/CellCoordinates.php b/tests/data/CellCoordinates.php
index 694856ccb3..78f841ef0c 100644
--- a/tests/data/CellCoordinates.php
+++ b/tests/data/CellCoordinates.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/CellExtractAllCellReferencesInRange.php b/tests/data/CellExtractAllCellReferencesInRange.php
index 192500ce4f..02ec9f8551 100644
--- a/tests/data/CellExtractAllCellReferencesInRange.php
+++ b/tests/data/CellExtractAllCellReferencesInRange.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/CellGetRangeBoundaries.php b/tests/data/CellGetRangeBoundaries.php
index 7a56b4c030..1cce2f35d0 100644
--- a/tests/data/CellGetRangeBoundaries.php
+++ b/tests/data/CellGetRangeBoundaries.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'Cell Range' => [
diff --git a/tests/data/CellMergeRangesInCollection.php b/tests/data/CellMergeRangesInCollection.php
index 0a7723ee00..3be59edc36 100644
--- a/tests/data/CellMergeRangesInCollection.php
+++ b/tests/data/CellMergeRangesInCollection.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/CellRangeBoundaries.php b/tests/data/CellRangeBoundaries.php
index 882f437cdd..d3804ebae1 100644
--- a/tests/data/CellRangeBoundaries.php
+++ b/tests/data/CellRangeBoundaries.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     'Cell Range' => [
         [
diff --git a/tests/data/CellRangeDimension.php b/tests/data/CellRangeDimension.php
index a3e15531cd..ca289179b3 100644
--- a/tests/data/CellRangeDimension.php
+++ b/tests/data/CellRangeDimension.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/CellSplitRange.php b/tests/data/CellSplitRange.php
index a7d701c3f2..ba2ab37ea7 100644
--- a/tests/data/CellSplitRange.php
+++ b/tests/data/CellSplitRange.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         [
diff --git a/tests/data/ColumnIndex.php b/tests/data/ColumnIndex.php
index 750ef823f0..0bb2bdc99f 100644
--- a/tests/data/ColumnIndex.php
+++ b/tests/data/ColumnIndex.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'A',
diff --git a/tests/data/ColumnString.php b/tests/data/ColumnString.php
index 78d21aaa73..1aaafe8298 100644
--- a/tests/data/ColumnString.php
+++ b/tests/data/ColumnString.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         1,
diff --git a/tests/data/CoordinateIsRange.php b/tests/data/CoordinateIsRange.php
index 4718bdce68..a0c44089f8 100644
--- a/tests/data/CoordinateIsRange.php
+++ b/tests/data/CoordinateIsRange.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         false,
diff --git a/tests/data/Functional/TypeAttributePreservation/Formula.php b/tests/data/Functional/TypeAttributePreservation/Formula.php
index c10e2a61b0..6f260da470 100644
--- a/tests/data/Functional/TypeAttributePreservation/Formula.php
+++ b/tests/data/Functional/TypeAttributePreservation/Formula.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         ['string'],
diff --git a/tests/data/ReferenceHelperFormulaUpdates.php b/tests/data/ReferenceHelperFormulaUpdates.php
index ef563f31c7..4dad6bf07e 100644
--- a/tests/data/ReferenceHelperFormulaUpdates.php
+++ b/tests/data/ReferenceHelperFormulaUpdates.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '=IF(A$1=0,0,A1/A$1)',
diff --git a/tests/data/ReferenceHelperFormulaUpdatesMultipleSheet.php b/tests/data/ReferenceHelperFormulaUpdatesMultipleSheet.php
index 9c59359d1c..f4f97e5fb8 100644
--- a/tests/data/ReferenceHelperFormulaUpdatesMultipleSheet.php
+++ b/tests/data/ReferenceHelperFormulaUpdatesMultipleSheet.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         "=IF('2020'!\$B1=\"\",\"-\",(('2020'!\$B1/'2019'!\$B1)-1))",
diff --git a/tests/data/Shared/CentimeterSizeToPixels.php b/tests/data/Shared/CentimeterSizeToPixels.php
index 6ef11d938d..ff519ba9df 100644
--- a/tests/data/Shared/CentimeterSizeToPixels.php
+++ b/tests/data/Shared/CentimeterSizeToPixels.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         3.7795275590999999,
diff --git a/tests/data/Shared/CodePage.php b/tests/data/Shared/CodePage.php
index ccb59f240a..eca9879f69 100644
--- a/tests/data/Shared/CodePage.php
+++ b/tests/data/Shared/CodePage.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     // ANSI Latin I (BIFF4-BIFF7)
     [
diff --git a/tests/data/Shared/Date/DateTimeToExcel.php b/tests/data/Shared/Date/DateTimeToExcel.php
index a2f537af3e..f5f754a759 100644
--- a/tests/data/Shared/Date/DateTimeToExcel.php
+++ b/tests/data/Shared/Date/DateTimeToExcel.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // DateTime object                          Result           Comments
 return [
     // Excel 1900 base calendar date
diff --git a/tests/data/Shared/Date/ExcelToTimestamp1900.php b/tests/data/Shared/Date/ExcelToTimestamp1900.php
index ffcd194f46..3c94a41aba 100644
--- a/tests/data/Shared/Date/ExcelToTimestamp1900.php
+++ b/tests/data/Shared/Date/ExcelToTimestamp1900.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Excel DateTimeStamp  Result            Comments
 return [
     // PHP 32-bit Earliest Date 14-Dec-1901
diff --git a/tests/data/Shared/Date/ExcelToTimestamp1900Timezone.php b/tests/data/Shared/Date/ExcelToTimestamp1900Timezone.php
index 0678723d9e..3eb7be2ae5 100644
--- a/tests/data/Shared/Date/ExcelToTimestamp1900Timezone.php
+++ b/tests/data/Shared/Date/ExcelToTimestamp1900Timezone.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Excel DateTimeStamp  Timezone               Result            Comments
 return [
     // 19-Dec-1960 00:00:00 EST => 19-Dec-1960 05:00:00 UTC
diff --git a/tests/data/Shared/Date/ExcelToTimestamp1904.php b/tests/data/Shared/Date/ExcelToTimestamp1904.php
index 82fcde1cf9..12a3999a91 100644
--- a/tests/data/Shared/Date/ExcelToTimestamp1904.php
+++ b/tests/data/Shared/Date/ExcelToTimestamp1904.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Excel DateTimeStamp        Result            Comments
 
 return [
diff --git a/tests/data/Shared/Date/FormatCodes.php b/tests/data/Shared/Date/FormatCodes.php
index b558874c52..8cd09172cc 100644
--- a/tests/data/Shared/Date/FormatCodes.php
+++ b/tests/data/Shared/Date/FormatCodes.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Excel Format Code                     Result
 return [
     [
diff --git a/tests/data/Shared/Date/FormattedPHPToExcel1900.php b/tests/data/Shared/Date/FormattedPHPToExcel1900.php
index 459954e197..3040418bf0 100644
--- a/tests/data/Shared/Date/FormattedPHPToExcel1900.php
+++ b/tests/data/Shared/Date/FormattedPHPToExcel1900.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Year   Month  Day  Hours  Minutes  Seconds  Result            Comments
 
 return [
diff --git a/tests/data/Shared/Date/TimestampToExcel1900.php b/tests/data/Shared/Date/TimestampToExcel1900.php
index fd94d44fc8..6206a89848 100644
--- a/tests/data/Shared/Date/TimestampToExcel1900.php
+++ b/tests/data/Shared/Date/TimestampToExcel1900.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Unix TimeStamp   Result           Comments
 
 return [
diff --git a/tests/data/Shared/Date/TimestampToExcel1904.php b/tests/data/Shared/Date/TimestampToExcel1904.php
index 43659a9400..24b714eef7 100644
--- a/tests/data/Shared/Date/TimestampToExcel1904.php
+++ b/tests/data/Shared/Date/TimestampToExcel1904.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // Excel DateTimeStamp  Result
 return [
     [
diff --git a/tests/data/Shared/FontSizeToPixels.php b/tests/data/Shared/FontSizeToPixels.php
index a222ec182a..3b6e7f7108 100644
--- a/tests/data/Shared/FontSizeToPixels.php
+++ b/tests/data/Shared/FontSizeToPixels.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         8,
diff --git a/tests/data/Shared/InchSizeToPixels.php b/tests/data/Shared/InchSizeToPixels.php
index f165460e87..1162addc2a 100644
--- a/tests/data/Shared/InchSizeToPixels.php
+++ b/tests/data/Shared/InchSizeToPixels.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         9.5999999999999996,
diff --git a/tests/data/Shared/PasswordHashes.php b/tests/data/Shared/PasswordHashes.php
index c46adf1427..5c697d22c2 100644
--- a/tests/data/Shared/PasswordHashes.php
+++ b/tests/data/Shared/PasswordHashes.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'BCDE',
diff --git a/tests/data/Shared/Trend/ExponentialBestFit.php b/tests/data/Shared/Trend/ExponentialBestFit.php
index ac1da739c6..04d8b89f5e 100644
--- a/tests/data/Shared/Trend/ExponentialBestFit.php
+++ b/tests/data/Shared/Trend/ExponentialBestFit.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'slope' => [0.8, 0.813512072856517],
diff --git a/tests/data/Shared/Trend/LinearBestFit.php b/tests/data/Shared/Trend/LinearBestFit.php
index b1be2f9a57..046fdb6ee1 100644
--- a/tests/data/Shared/Trend/LinearBestFit.php
+++ b/tests/data/Shared/Trend/LinearBestFit.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         'slope' => [-1.1, -1.1064189189190],
diff --git a/tests/data/Style/Color/ColorChangeBrightness.php b/tests/data/Style/Color/ColorChangeBrightness.php
index 1c552e157d..6d9f038360 100644
--- a/tests/data/Style/Color/ColorChangeBrightness.php
+++ b/tests/data/Style/Color/ColorChangeBrightness.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     // RGBA
     [
diff --git a/tests/data/Style/Color/ColorGetBlue.php b/tests/data/Style/Color/ColorGetBlue.php
index ff4d9fb7a8..83fbdc774a 100644
--- a/tests/data/Style/Color/ColorGetBlue.php
+++ b/tests/data/Style/Color/ColorGetBlue.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     // RGBA (hex)
     [
diff --git a/tests/data/Style/Color/ColorGetGreen.php b/tests/data/Style/Color/ColorGetGreen.php
index 5ab7b9dc76..d0e60d70e9 100644
--- a/tests/data/Style/Color/ColorGetGreen.php
+++ b/tests/data/Style/Color/ColorGetGreen.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     // RGBA (hex)
     [
diff --git a/tests/data/Style/Color/ColorGetRed.php b/tests/data/Style/Color/ColorGetRed.php
index cad0f5c35e..1187d45062 100644
--- a/tests/data/Style/Color/ColorGetRed.php
+++ b/tests/data/Style/Color/ColorGetRed.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     // RGBA (hex)
     [
diff --git a/tests/data/Style/NumberFormat.php b/tests/data/Style/NumberFormat.php
index 733f8c469b..ae734178df 100644
--- a/tests/data/Style/NumberFormat.php
+++ b/tests/data/Style/NumberFormat.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
 
 //  value, format, result
diff --git a/tests/data/Style/NumberFormatDates.php b/tests/data/Style/NumberFormatDates.php
index 632b967e03..c1f8eb1b8a 100644
--- a/tests/data/Style/NumberFormatDates.php
+++ b/tests/data/Style/NumberFormatDates.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 return [
     [
         '19-12-1960 01:30:00',
diff --git a/tests/data/Style/NumberFormatFractions.php b/tests/data/Style/NumberFormatFractions.php
index e7d4cfa69b..4daafca2ac 100644
--- a/tests/data/Style/NumberFormatFractions.php
+++ b/tests/data/Style/NumberFormatFractions.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 //  value, format, result
 
 return [