def test_startServiceUsesGlobalReactor(self):
        """
        L{TimerService.startService} uses L{internet._maybeGlobalReactor} to
        choose the reactor to pass to L{task.LoopingCall}
        uses the global reactor.
        """
        otherClock = task.Clock()
        def getOtherClock(maybeReactor):
            return otherClock
        self.patch(internet, "_maybeGlobalReactor", getOtherClock)
        self.timer.startService()
        self.assertIdentical(otherClock, self.timer._loop.clock)

        L{TimerService.startService} uses L{internet._maybeGlobalReactor} to
        choose the reactor to pass to L{task.LoopingCall}
        uses the global reactor.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/test/test_internet.py