'When canceling a L{Deferred} from a L{DeferredLock} that already
has the lock, the cancel should have no effect.'

def test_cancelLockAfterAcquired(self):

    def _failOnErrback(_):
        self.fail('Unexpected    errback    call!')
    lock = defer.DeferredLock()
    d = lock.acquire()
    d.addErrback(_failOnErrback)
    d.cancel()
