At the moment seen 100% of the time on Travis CI for master. Locally reproduced once by tinkering with -Xmx.
Failures look like this:
The test counts org.geotools.jdbc WARNING messages. The cause of the failure is leakage from other tests collected by the finalizer thread at a nondeterministic time. For example:
The workaround is to add a guard so the test does not count log messages with source method name "finalize".