This has happened several times on Jenkins, typically on SSLMigrationTest.testDistribSearch, but probably on other tests as well.
The symptom is: the test framework never terminates, it also reports an incorrect hung test.
The problem is that the actual forked JVM is hung on reading stdin, waiting for the next test suite (no test thread is present); the master process is hung on receiving data from the forked jvm (both the events file and stdout spill is truncated in the middle of a test). The last output is:
Overall, it looks insane – there are flushes after each test completes (normally or not), there are tests following the one that last reported output and before dynamic suites on stdin.
I have no idea. The best explanation is insane – looks like the test thread just died in the middle of executing Java code...