Tests get run multiple times when test contains when clause with enums AND using maxParallelForks

[mightyguava]

Kotest version: 5.8.1

This is one of the weirder bugs I've seen.

Repro here, containing a single commit on top of the kotest-examples-multiplatform repo main.

If you run ./gradlew cleanJvmTest jvmTest, you'll see that every test within the module is run twice. This is also visible from build/reports/tests/jvmTest/index.html. If maxParallelForks is set to 1, this issue does not occur.

If you copy the test case in WhenTest, each new copy of the test case will cause all tests to be run an additional time.

Based on trial and error, I narrowed this down to when clauses being added to the test that operate on an enum. Looking at the compiled classes, I suspect it has something to do with this $WhenMappings class that is generated, e.g.

build/classes/kotlin/jvm/test/io/kotest/examples/mpp/whendupe/BarTests$1$1$WhenMappings.class

Each test case that uses a when on an enum seems to generate a extra inner class... and my hypothesis is that Kotest's runner (or JUnit framework? or Gradle?) isn't deduping this with the outer class properly.