Add Kotlin specific assertion helpers

build.gradle

@@ -187,6 +187,12 @@ allprojects { subproj ->
 		options.compilerArgs += '-parameters'
 	}
 
+	tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile) {
+		kotlinOptions {
+			jvmTarget = '1.8'
+		}
+	}
+
 	checkstyle {
 		toolVersion = '7.6'
 	}
@@ -537,6 +543,13 @@ subprojects { subproj ->
 			replaceRegex 'Empty line between last method and class closure', /\n([\s]+)}\n}\n$/, '\n$1}\n\n}\n'
 			replaceRegex 'Remove line breaks between consecutive closing parentheses', /\)\n[\s]+\)\n/, '))\n'
 		}
+
+		kotlin {
+			ktlint("0.9.0")
+			licenseHeaderFile headerFile
+			trimTrailingWhitespace()
+			endWithNewline()
+		}
 	}
 
 	afterEvaluate {

documentation/documentation.gradle

@@ -39,6 +39,7 @@ dependencies {
 	testImplementation(project(path: ':junit-jupiter-params', configuration: 'shadow'))
 	testImplementation(project(':junit-platform-runner'))
 	testImplementation(project(':junit-platform-launcher'))
+	testImplementation("org.jetbrains.kotlin:kotlin-stdlib")
 
 	// Include junit-platform-console so that the JUnit Gradle plugin
 	// uses the local version of the ConsoleLauncher.
@@ -91,6 +92,7 @@ asciidoctor {
 				'revnumber' : project.version,
 				'mainDir': project.sourceSets.main.java.srcDirs[0],
 				'testDir': project.sourceSets.test.java.srcDirs[0],
+				'kotlinTestDir' : project.sourceSets.test.kotlin.srcDirs[0],
 				'generatedAsciiDocInputDir': generatedAsciiDocInputDir,
 				'testResourcesDir': project.sourceSets.test.resources.srcDirs[0],
 				'outdir': outputDir.absolutePath,

documentation/src/docs/asciidoc/release-notes-5.1.0-M1.adoc

@@ -3,7 +3,7 @@
 
 *Date of Release:* ❓
 
-*Scope:* ❓
+*Scope:* Addition of Kotlin assertion helpers.
 
 For a complete list of all _closed_ issues and pull requests for this release, consult the
 link:{junit5-repo}+/milestone/14?closed=1+[5.1 M1] milestone page in the JUnit repository
@@ -68,7 +68,9 @@ on GitHub.
 * The `JupiterTestEngine` supports the new JUnit Platform `ModuleSelector` for selecting
   Java 9 modules.
   - This is an alternative to the existing classpath scanning support.
-
+* New Kotlin friendly assertions added as top-level functions in the `org.junit.jupiter.api` package.
+** `assertAll` that takes `Stream<() -> Unit>` or `vararg () -> Unit`.
+** `assertThrow` that uses Kotlin reified generics.
 
 [[release-notes-5.1.0-junit-vintage]]
 ==== JUnit Vintage

documentation/src/docs/asciidoc/writing-tests.adoc

@@ -94,6 +94,16 @@ are `static` methods in the `{Assertions}` class.
 include::{testDir}/example/AssertionsDemo.java[tags=user_guide]
 ----
 
+JUnit Jupiter also comes with a few assertion methods that lend themselves well to being
+used in https://kotlinlang.org/[Kotlin]. All JUnit Jupiter Kotlin assertions are top-level
+functions in the `org.junit.jupiter.api` package.
+
+// TODO: Change to using kotlin language highlighting after switch to rouge syntax highlighter
+[source,java,indent=0]
+----
+include::{kotlinTestDir}/example/AssertionsDemoKotlin.kt[tags=user_guide]
+----
+
 [[writing-tests-assertions-third-party]]
 ==== Third-party Assertion Libraries
 

documentation/src/test/java/example/AssertionsDemo.java

@@ -143,23 +143,3 @@ private static String greeting() {
 }
 // end::user_guide[]
 // @formatter:on
-
-class Person {
-
-	private final String firstName;
-	private final String lastName;
-
-	Person(String firstName, String lastName) {
-		this.firstName = firstName;
-		this.lastName = lastName;
-	}
-
-	String getFirstName() {
-		return firstName;
-	}
-
-	String getLastName() {
-		return lastName;
-	}
-
-}

documentation/src/test/kotlin/example/AssertionsDemoKotlin.kt

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2015-2017 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * http://www.eclipse.org/legal/epl-v20.html
+ */
+package example
+
+// tag::user_guide[]
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertAll
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.assertThrows
+
+class AssertionsDemoKotlin {
+
+    // end::user_guide[]
+    val person = Person("John", "Doe")
+    val people = setOf(person, Person("James", "Doe"))
+
+    // tag::user_guide[]
+    @Test
+    fun `grouped assertions`() {
+        assertAll("person",
+            { assertEquals("John", person.firstName) },
+            { assertEquals("Doe", person.lastName) }
+        )
+    }
+
+    @Test
+    fun `exception testing`() {
+        val exception = assertThrows<IllegalArgumentException> ("Should throw an exception") {
+            throw IllegalArgumentException("a message")
+        }
+        assertEquals("a message", exception.message)
+    }
+
+    @Test
+    fun `assertions from a stream`() {
+        assertAll(
+            "people with name starting with J",
+            people
+                .stream()
+                .map {
+                    // This mapping returns Stream<() -> Unit>
+                    { assertTrue(it.firstName.startsWith("J")) }
+                }
+        )
+    }
+}
+// end::user_guide[]

documentation/src/test/kotlin/example/Person.kt

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2015-2017 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * http://www.eclipse.org/legal/epl-v20.html
+ */
+package example
+
+data class Person(val firstName: String, val lastName: String)

junit-jupiter-api/junit-jupiter-api.gradle

@@ -1,12 +1,32 @@
 dependencies {
 	api("org.opentest4j:opentest4j:${ota4jVersion}")
-	api(project(':junit-platform-commons'))
+	api(project(":junit-platform-commons"))
+	compileOnly("org.jetbrains.kotlin:kotlin-stdlib")
 }
 
 jar {
 	manifest {
 		attributes(
-			'Automatic-Module-Name': 'org.junit.jupiter.api'
+				'Automatic-Module-Name': 'org.junit.jupiter.api'
 		)
 	}
 }
+
+configurations {
+	apiElements {
+		/*
+		* Needed to configure kotlin to work correctly with the "java-library" plugin.
+		* See:
+		* https://docs.gradle.org/current/userguide/java_library_plugin.html#sec:java_library_known_issues
+		* https://youtrack.jetbrains.com/issue/KT-18497
+		*/
+		outgoing
+			.variants
+			.getByName("classes")
+			.artifact(
+				"file" : compileKotlin.destinationDir,
+				"type" : "java-classes-directory",
+				"builtBy" : compileKotlin
+			)
+	}
+}

junit-jupiter-api/src/main/java/org/junit/jupiter/api/Assertions.java

@@ -29,6 +29,9 @@
  * {@code Assertions} is a collection of utility methods that support asserting
  * conditions in tests.
  *
+ * <p>Additional <a href="https://kotlinlang.org/">Kotlin</a> assertions can be found
+ * as top-level functions on the {@link org.junit.jupiter.api} package.
+ *
  * <p>Unless otherwise noted, a <em>failed</em> assertion will throw an
  * {@link org.opentest4j.AssertionFailedError} or a subclass thereof.
  *

junit-jupiter-api/src/main/kotlin/org/junit/jupiter/api/Assertions.kt

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2015-2017 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * http://www.eclipse.org/legal/epl-v20.html
+ */
+@file:API(status = EXPERIMENTAL, since = "5.1")
+package org.junit.jupiter.api
+
+import org.apiguardian.api.API
+import org.apiguardian.api.API.Status.EXPERIMENTAL
+import org.junit.jupiter.api.function.Executable
+import java.util.function.Supplier
+import java.util.stream.Stream
+
+/**
+ * [Stream] of functions to be executed.
+ */
+private typealias ExecutableStream = Stream<() -> Unit>
+private fun ExecutableStream.convert() = map { Executable(it) }
+
+/**
+ * @see Assertions.assertAll
+ */
+fun assertAll(executables: ExecutableStream) =
+    Assertions.assertAll(executables.convert())
+
+/**
+ * @see Assertions.assertAll
+ */
+fun assertAll(heading: String?, executables: ExecutableStream) =
+    Assertions.assertAll(heading, executables.convert())
+
+/**
+ * @see Assertions.assertAll
+ */
+fun assertAll(vararg executables: () -> Unit) =
+    assertAll(executables.toList().stream())
+
+/**
+ * @see Assertions.assertAll
+ */
+fun assertAll(heading: String?, vararg executables: () -> Unit) =
+    assertAll(heading, executables.toList().stream())
+
+/**
+ * Example usage:
+ * ```kotlin
+ * val exception = assertThrows<IllegalArgumentException> {
+ *     throw IllegalArgumentException("Talk to a duck")
+ * }
+ * assertEquals("Talk to a duck", exception.message)
+ * ```
+ * @see Assertions.assertThrows
+ */
+inline fun <reified T : Throwable> assertThrows(noinline executable: () -> Unit): T =
+    Assertions.assertThrows(T::class.java, Executable(executable))
+
+/**
+ * Example usage:
+ * ```kotlin
+ * val exception = assertThrows<IllegalArgumentException>("Should throw an Exception") {
+ *     throw IllegalArgumentException("Talk to a duck")
+ * }
+ * assertEquals("Talk to a duck", exception.message)
+ * ```
+ * @see Assertions.assertThrows
+ */
+inline fun <reified T : Throwable> assertThrows(message: String, noinline executable: () -> Unit): T =
+    assertThrows({ message }, executable)
+
+/**
+ * Example usage:
+ * ```kotlin
+ * val exception = assertThrows<IllegalArgumentException>({ "Should throw an Exception" }) {
+ *     throw IllegalArgumentException("Talk to a duck")
+ * }
+ * assertEquals("Talk to a duck", exception.message)
+ * ```
+ * @see Assertions.assertThrows
+ */
+inline fun <reified T : Throwable> assertThrows(noinline message: () -> String, noinline executable: () -> Unit): T =
+    Assertions.assertThrows(T::class.java, Executable(executable), Supplier {
+        /*
+         * This is a hacky workaround due to a bug in how the JDK 9 JavaDoc code generator interacts with the
+         * generated Kotlin Bytecode.
+         * https://youtrack.jetbrains.com/issue/KT-20025
+         */
+        message()
+    })

junit-jupiter-engine/junit-jupiter-engine.gradle

@@ -47,7 +47,7 @@ dependencies {
 	testImplementation(project(path: ':junit-platform-engine', configuration: 'testArtifacts'))
 	testImplementation("org.assertj:assertj-core:${assertJVersion}")
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
-	testImplementation("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
+	testImplementation("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
 
 	// Include junit-platform-console so that the JUnit Gradle plugin
 	// uses the local version of the ConsoleLauncher.

junit-jupiter-engine/src/test/java/org/junit/jupiter/api/AssertAllAssertionsTests.java

@@ -149,7 +149,7 @@ void assertAllWithExecutableThatThrowsBlacklistedException() {
 	}
 
 	@SafeVarargs
-	private static void assertExpectedExceptionTypes(MultipleFailuresError multipleFailuresError,
+	static void assertExpectedExceptionTypes(MultipleFailuresError multipleFailuresError,
 			Class<? extends Throwable>... exceptionTypes) {
 
 		assertNotNull(multipleFailuresError, "MultipleFailuresError");