There are a couple of problems with failure behavior of the test worker process. I can observe them with TestNG but they might be also reproducable with JUnit.

If the user test runtime classpath contains conflicted libraries here's what may happen:

1. Gradle fails the build saying that 'some tests failed' and pointing out to the html report. This is wrong on its own because there's no report and no tests have been run. This is already reported here: GRADLE-1710
2. Gradle does not show useful stack trace with -s. It only informs that the worker process misbehaved. The only way to find out why the worker process misbehaved is to run with --debug but it is inconvenient because -d output is hard to investigate (lots of stuff).
3. The debug output when investigated shows:

• First, TestNGTestResultProcessorAdapter fails in constructor (root cause being java.lang.VerifyError or something smiliar)
• Then, there are various NPE stack traces, possibly caused by the earlier TestNGTestResultProcessorAdapter failure
• I would expect to see only a relevant stack trace (no NPEs)

The debug output from the reproducible sample is here: https://gist.github.com/46f391499ed5c418810e The problem in the sample was that there was both: google-collections and guava on the test runtime classpath and this combination was causing java.lang.VerifyError.

The user who reported this issue originally was convinced that it was a Gradle problem and the root cause was incompatibility of Gradle's classpath (which has guava) with test runtime classpath.