This is an excerpt of test/src/fns-tests.el with a few lines added at
the end to invoke Testcover. It contains two nearly identical tests
which should both pass, but one passes and one fails. If you then edit
the file and comment out test-cycle-assoc (the one that passes) and run
the test again, then the failing test will pass. I've reproduced it both
in batch mode (without TEST_LOAD_EL=no) and interactively.