def test_startServiceRunsCallImmediately(self):
        """
        When L{TimerService.startService} is called, it calls the function
        immediately.
        """
        result = []
        self.timer.call = (result.append, (None,), {})
        self.timer.startService()
        self.assertEqual([None], result)

        When L{TimerService.startService} is called, it calls the function
        immediately.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/test/test_internet.py