NoClassDefFoundError when trying to execute JUnit 4 test in Intellij 2018.2.RC

When trying to execute a very simple Hello World test in Android, using KotlinTest:

class ExampleUnitTest : FreeSpec() {

init {
    "Test" {
        2 + 2 shouldBe 4
    }
   }
}

When trying to execute this in IntelliJ, by clicking the green icon, I get the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: org/junit/platform/launcher/TestExecutionListener
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at com.intellij.junit5.JUnit5IdeaTestRunner.createListeners(JUnit5IdeaTestRunner.java:39)
    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:45)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.lang.ClassNotFoundException: org.junit.platform.launcher.TestExecutionListener
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 16 more

Process finished with exit code 1

I'm using this dependency:

testImplementation "io.kotlintest:kotlintest-runner-junit4:3.1.8"

JUnit 4 is necessary because Android doesn't support JUnit 5 yet.

When executing ./gradlew test it works correctly, so I assume this is a problem with IntelliJ only?

I'm unsure of what is causing this, but after hours of useless research, I've found a workaround to solve this issue.

It seems to be a bug in IntelliJ IDEA 2018.2.RC, that causes it to execute code using JUnit 5 anyways. It looks like that it does that because it doesn't find any other TestExecutor in the classpath.

A Workaround to this is forcing your UnitTest to be compiled after IntelliJ builds it.

---

For that, edit your tests configuration:

And add a Gradle task to compileDebugUnitTestKotlin:

After this, your tests should become green again.