Working on removing the remainder of JUnit 4 from spock-core, I have encountered @groovy.transform.NotYetImplemented which transformation is wired to junit.framework.AssertionFailedError. It's deprecated in favor of @groovy.test.NotYetImplemented, but the corresponding transformation is also wired to AssertionFailedError. That makes its usage without JUnit 4 (and also testing in Spock 2) harder
It would be good to check at runtime which exception is available at classpath to work also in the situation without JUnit 4 on classpath.
Btw, I don't know which component should I choose. There is no groovy-test component.