How to run kotlintest tests using the Gradle Kotlin DSL?

What do I want?

I want to run my tests using kotlintest, and I succeeded in running them from IntelliJ by clicking the icon next to the test class. I also have JUnit 5 tests in my project. I am now starting to use the Gradle Kotlin DSL, and I managed to run the Gradle task check which executed the JUnit 5 tasks.

What is the problem?

The kotlintest test is not run! It is not discovered by Gradle it seems, as a failing test lets the Gradle task succeed. So,

How to run kotlintest tests using the Gradle Kotlin DSL while also using JUnit 5?

What did I try?

How can I run kotlintest tests with gradle? is essentially the old version of the question but already obsolete since using different technology: JUnit 4 and Gradle instead of the Gradle Kotlin DSL. All other question I could find are either for JUnit 4, or JUnit 5 without kotlintest.

Project setup

I am using Gradle 4.6. My test is

import io.kotlintest.matchers.exactly
import io.kotlintest.matchers.shouldBe
import io.kotlintest.specs.FunSpec

class KotlinTest: FunSpec() {

    init {
        testCalculate()
    }

    /** This failing test will not fail the Gradle check. */
    fun testCalculate() = test("one plus one is two") {
        (1+1).toDouble() shouldBe exactly(42.0)
    }

}

and my build.gradle.kts 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 = "mypackage"
version = "0.0"

// JUnit 5
buildscript {
    repositories {
        mavenCentral()
        jcenter()
    }
    dependencies {
        classpath("org.junit.platform:junit-platform-gradle-plugin:1.1.0")
    }
}

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

// Kotlin configuration.
plugins {
    application
    kotlin("jvm") version "1.2.30"
    java // Required by at least JUnit.
}

application {
    mainClassName = "mypackage.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:5.1.0")
    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.1.0")
    testRuntime("org.junit.platform:junit-platform-console:1.1.0")

    // Kotlintests are not run anyway when using JUnit 5 as well.
    testCompile("io.kotlintest:kotlintest:2.0.7")

}

repositories {
    jcenter()
}

PS Complete project at GitHub.

Similar to @PhPirate's answer, to use KotlinTest 3.0.x with gradle, you need to.

1. Add the gradle plugin for junit 5 (also called the junit platform)
2. Add the gradle junit plugin to the classpath of your buildscript
3. Add KotlinTest junit5 runner to your test dependencies.

The first two steps are common for any project that uses junit platform - which includes junit5 itself, KotlinTest, Spek, and so on.

A basic gradle config looks like this:

apply plugin: 'org.junit.platform.gradle.plugin'

buildscript {
    ext.kotlin_version = '1.2.31'
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
        classpath "org.junit.platform:junit-platform-gradle-plugin:1.1.0"
    }
}

dependencies {
    testCompile 'io.kotlintest:kotlintest-runner-junit5:3.0.2'
}

You could also clone the gradle sample repo here which has a simple gradle project configured with KotlinTest.