Since the change to async logger, this test fails 100% of the time for me locally. [~steve_rowe] confirmed that it fails for him too so it's not something weird in my environment.
Why there are no reports from Jenkins of this failure is a mystery.
The test succeeds, but there is a thread leak and the stack trace points to "lmax.disruptor" which is certainly a part of the async logging.
And why, if this is something generic, it doesn't fail many many tests is another mystery so I suspect it's something specific to the test, perhaps having to do with mocking the metric reporter, but that's a wild shot in the dark.
My working hypothesis is that "something isn't being closed/shutdown correctly", but that's...a little vague.
Sep 04, 2018 9:38:00 AM com.carrotsearch.randomizedtesting.ThreadLeakControl checkThreadLeaks
WARNING: Will linger awaiting termination of 1 leaked thread(s).
Sep 04, 2018 9:38:20 AM com.carrotsearch.randomizedtesting.ThreadLeakControl checkThreadLeaks
SEVERE: 1 thread leaked from SUITE scope at org.apache.solr.metrics.SolrMetricReporterTest:
1) Thread[id=14, name=Log4j2-TF-1-AsyncLoggerConfig--1, state=TIMED_WAITING, group=TGRP-SolrMetricReporterTest]
at sun.misc.Unsafe.park(Native Method)