How do I use the native JUnit 5 support in Gradle with the Kotlin DSL?

Question

I want to use the built-in JUnit 5 with the Gradle Kotlin DSL, because during build I get this warning:

WARNING: The junit-platform-gradle-plugin is deprecated and will be discontinued in JUnit Platform 1.3.
Please use Gradle's native support for running tests on the JUnit Platform (requires Gradle 4.6 or higher):
https://junit.org/junit5/docs/current/user-guide/#running-tests-build-gradle

That links tells me to put

test {
    useJUnitPlatform()
}

in my build.gradle, but what is the syntax for build.gradle.kts?

My current build file is

import org.gradle.api.plugins.ExtensionAware

import org.junit.platform.gradle.plugin.FiltersExtension
import org.junit.platform.gradle.plugin.EnginesExtension
import org.junit.platform.gradle.plugin.JUnitPlatformExtension

group = "com.example"
version = "0.0"

// JUnit 5
buildscript {
    repositories {
        mavenCentral()
        jcenter()
    }
    dependencies {
        classpath("org.junit.platform:junit-platform-gradle-plugin:1.2.0")
    }
}

apply {
    plugin("org.junit.platform.gradle.plugin")
}

// Kotlin configuration.
plugins {

    val kotlinVersion = "1.2.41"

    application
    kotlin("jvm") version kotlinVersion
    java // Required by at least JUnit.

    // Plugin which checks for dependency updates with help/dependencyUpdates task.
    id("com.github.ben-manes.versions") version "0.17.0"

    // Plugin which can update Gradle dependencies, use help/useLatestVersions
    id("se.patrikerdes.use-latest-versions") version "0.2.1"

}

application {
    mainClassName = "com.example.HelloWorld"
}

dependencies {
    compile(kotlin("stdlib"))
    // To "prevent strange errors".
    compile(kotlin("reflect"))
    // Kotlin reflection.
    compile(kotlin("test"))
    compile(kotlin("test-junit"))

    // JUnit 5
    testImplementation("org.junit.jupiter:junit-jupiter-api:5.2.0")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.2.0")
    testRuntime("org.junit.platform:junit-platform-console:1.2.0")

    // Kotlintest
    testCompile("io.kotlintest:kotlintest-core:3.1.0-RC2")
    testCompile("io.kotlintest:kotlintest-assertions:3.1.0-RC2")
    testCompile("io.kotlintest:kotlintest-runner-junit5:3.1.0-RC2")

}

repositories {
    mavenCentral()
    mavenLocal()
    jcenter()
}

(The following is some blabla because this question 'contains mostly code'). I tried to find documentation on how to customize tasks in the Kotlin DSL, but I couldn't find any. In normal Groovy you can just write the name of the task and then change things in the block, but the Kotlin DSL doesn't recognise the task as such, unresolved reference.

Also, this question is related but asks for creating of new tasks, instead of customize existing tasks: How do I overwrite a task in gradle kotlin-dsl

Here is a solution for normal Gradle.

Answer 1

[Edit april 2019] As Pedro has found, three months after I asked this question Gradle actually created a user guide for the Kotlin DSL which can be visited at https://docs.gradle.org/current/userguide/kotlin_dsl.html

They also added a migration guide from Groovy to Kotlin at https://guides.gradle.org/migrating-build-logic-from-groovy-to-kotlin/

Answer:

The syntax you ask for is

tasks.test {
    // Use the built-in JUnit support of Gradle.
    useJUnitPlatform()
}

which I figured out from this example file from the Kotlin DSL GitHub, or you can use

tasks.withType<Test> {
    useJUnitPlatform()
}

which is used in the this official userguide which was created a couple of months after this answer was written (thanks to Pedro's answer for noting this).

But in any case you actually are still using the buildscript block, which is a bit deprecated itself, use the new plugins DSL instead (docs). New build.gradle.kts becomes

group = "com.example"
version = "0.0"

plugins {

    val kotlinVersion = "1.2.41"

    application
    kotlin("jvm") version kotlinVersion
    java // Required by at least JUnit.

    // Plugin which checks for dependency updates with help/dependencyUpdates task.
    id("com.github.ben-manes.versions") version "0.17.0"

    // Plugin which can update Gradle dependencies, use help/useLatestVersions
    id("se.patrikerdes.use-latest-versions") version "0.2.1"
}

application {
    mainClassName = "com.example.HelloWorld"
}

dependencies {
    compile(kotlin("stdlib"))
    // To "prevent strange errors".
    compile(kotlin("reflect"))
    // Kotlin reflection.
    compile(kotlin("test"))
    compile(kotlin("test-junit"))

    // JUnit 5
    testImplementation("org.junit.jupiter:junit-jupiter-api:5.2.0")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.2.0")
    testRuntime("org.junit.platform:junit-platform-console:1.2.0")

    // Kotlintest
    testCompile("io.kotlintest:kotlintest-core:3.1.0-RC2")
    testCompile("io.kotlintest:kotlintest-assertions:3.1.0-RC2")
    testCompile("io.kotlintest:kotlintest-runner-junit5:3.1.0-RC2")

}

repositories {
    mavenCentral()
    mavenLocal()
    jcenter()
}

tasks {
    // Use the native JUnit support of Gradle.
    "test"(Test::class) {
        useJUnitPlatform()
    }
}

(Since the Gradle Kotlin DSL has almost no documentation at all except a few (undocumented) example files on GitHub, I'm documenting a few common examples here.)

(Complete example project at GitHub, self-promotion...)