def test_pickleTimerServiceNotPickleLoopFinished(self):
        """
        When pickling L{internet.TimerService}, it won't pickle
        L{internet.TimerService._loopFinished}.
        """
        # We need a pickleable callable to test pickling TimerService. So we
        # can't use self.timer
        timer = TimerService(1, fakeTargetFunction)
        timer.startService()
        dumpedTimer = pickle.dumps(timer)
        timer.stopService()
        loadedTimer = pickle.loads(dumpedTimer)
        nothing = object()
        value = getattr(loadedTimer, "_loopFinished", nothing)
        self.assertIdentical(nothing, value)

        When pickling L{internet.TimerService}, it won't pickle
        L{internet.TimerService._loopFinished}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/test/test_internet.py