Fails to discover the used test engine.

[jcornaz]

Junit5 is a platform used by many different test engines.

For example, I'm using Spek which as for engine id: "spek2".

But pitest (using pitest-junit5-plugin) only triggers test discovery of the junit-jupiter engine.

As a result, I see the following exception:

WARNING: TestEngine with ID 'junit-jupiter' failed to discover tests
java.lang.NoClassDefFoundError: org/junit/jupiter/api/extension/ExtensionContext
        at org.junit.
2:45:14 PM PIT >> INFO : MINION : jupiter.engine.JupiterTestEngine.discover(JupiterTestEngine.java:66)
        at org.junit.platform.launcher.core.DefaultLauncher.discoverEngineRoot(DefaultLauncher.java:168)
        at org.junit.platform.launcher.core.DefaultLauncher.discoverRoot(DefaultLauncher.java:
2:45:14 PM PIT >> INFO : MINION : 155)
        at org.junit.platform.launcher.core.DefaultLauncher.discover(DefaultLauncher.java:120)
        at org.pitest.junit5.JUnit5TestUnitFinder.findTestUnits(JUnit5TestUnitFinder.java:49)
        at org.pitest.testapi.execute.FindTestUnits.findTestUnits(FindTestUnits.
2:45:14 PM PIT >> INFO : MINION : java:57)
        at org.pitest.testapi.execute.FindTestUnits.getTestUnits(FindTestUnits.java:40)
        at org.pitest.testapi.execute.FindTestUnits.findTestUnitsForAllSuppliedClasses(FindTestUnits.java:29)
        at org.pitest.coverage.execute.CoverageMinion.discoverTests
2:45:14 PM PIT >> INFO : MINION : (CoverageMinion.java:157)
        at org.pitest.coverage.execute.CoverageMinion.getTestsFromParent(CoverageMinion.java:138)
        at org.pitest.coverage.execute.CoverageMinion.main(CoverageMinion.java:84)
Caused by: java.lang.ClassNotFoundException: org.junit.jupit
2:45:14 PM PIT >> INFO : MINION : er.api.extension.ExtensionContext
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338)
        at java.lang.ClassLoader.loadC
2:45:14 PM PIT >> INFO : MINION : lass(ClassLoader.java:357)
        ... 11 more

And no coverage is found.

(This is related to hcoles/pitest#455)