def testCallLater(self):
        """
        Test that calls can be scheduled for later with the fake clock and
        hands back an L{IDelayedCall}.
        """
        c = task.Clock()
        call = c.callLater(1, lambda a, b: None, 1, b=2)
        self.assertTrue(interfaces.IDelayedCall.providedBy(call))
        self.assertEqual(call.getTime(), 1)
        self.assertTrue(call.active())

        Test that calls can be scheduled for later with the fake clock and
        hands back an L{IDelayedCall}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_task.py