While I like the idea of adding an option to force a garbage collection after running each time, I don't like how unittest is growing :-( It looks more and more like regrtest and I hate regrtest (I reworked its code recently to create a less ugly "libregrtes").
Once Antoine Pitrou proposed to add "plugins" to unittest. I agree that we need a gate between unittest and all other test frameworks: nose, py.test, testtools/testrepository/testr, etc.
Seriously, don't you think that something is wrong with such API?
def __init__(self, module='__main__', defaultTest=None, argv=None,
testRunner=None, testLoader=loader.defaultTestLoader,
exit=True, verbosity=1, failfast=None, catchbreak=None,
buffer=None, warnings=None, *, tb_locals=False,
gc_enabled=False):