Testing crashes because there is no TestEngine

[StanislasGaitUp]

After cloning the repo and updating to gradle 3.2.0, I have had this crash when starting the tests.

Exception in thread "main" org.junit.platform.commons.util.PreconditionViolationException: Cannot create Launcher without at least one TestEngine; consider adding an engine implementation JAR to the classpath
	at org.junit.platform.commons.util.Preconditions.condition(Preconditions.java:285)
	at org.junit.platform.launcher.core.DefaultLauncher.<init>(DefaultLauncher.java:55)
	at org.junit.platform.launcher.core.LauncherFactory.create(LauncherFactory.java:59)
	at org.jetbrains.spek.tooling.runner.junit.JUnitPlatformSpekRunner.run(JUnitPlatformSpekRunner.kt:66)
	at org.jetbrains.spek.tooling.MainKt.main(Main.kt:58)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.application.AppMainV2.main(AppMainV2.java:131)