LuceneTestCase.assumeWorkingMmap method is testing the directory, which is already tested, not the factory.
You misunderstood that. The assumeWorkingMmap is a check that unmapping works at all. If not, it disables the test - and that is what I wanted. Your test does not work if unmapping does not work, so it must be disabled if this is the case (On windows without unmapping the test Framework will complain about still open files after core startup...). assumeWorkingMmap takes care of that.
Nevertheless, the test is not needed, lets go without it! I will commit the no-test patch soon. Thanks!