I think the message here on the assert is overkill.  If we have only one assert per test, and the test method name is descriptive of the condition we are looking for, and the test itself is only 2 lines (get the path, call the assert), then its enough to rely on the test name to tell us what sort of condition is failed when the test fails.

In other words, I would have called this test:

  testIsBare_ArbitraryDirectoryIsBare()

and the one after it:

  testNotBare_HasDotGitNotBare()

etc.  FWIW, if you are copying style from another test that uses these test00N_ prefixes, that's an old style that was a horrible mistake on my part when I started JGit.  I was trying to mimic the style of the C Git test suite.  It was a bad idea.