Fix: Include tests directory when running php-cs-fixer

Author: localheinz

.php_cs.dist

@@ -163,5 +163,6 @@ return PhpCsFixer\Config::create()
         PhpCsFixer\Finder::create()
         ->files()
         ->in(__DIR__ . '/src')
+        ->in(__DIR__ . '/tests')
         ->notName('*.phpt')
     );