def test_cancelLockBeforeAcquired(self):
        """
        When canceling a L{Deferred} from a L{DeferredLock} that does not
        yet have the lock (i.e., the L{Deferred} has not fired), the cancel
        should cause a L{defer.CancelledError} failure.
        """
        lock = defer.DeferredLock()
        lock.acquire()
        d = lock.acquire()
        d.cancel()
        self.assertImmediateFailure(d, defer.CancelledError)

        When canceling a L{Deferred} from a L{DeferredLock} that does not
        yet have the lock (i.e., the L{Deferred} has not fired), the cancel
        should cause a L{defer.CancelledError} failure.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_defer.py