def test_cancelDeferredListWithOriginalDeferreds(self):
        """
        Cancelling a L{defer.DeferredList} will cancel the original
        L{defer.Deferred}s passed in.
        """
        deferredOne = defer.Deferred()
        deferredTwo = defer.Deferred()
        argumentList = [deferredOne, deferredTwo]
        deferredList = defer.DeferredList(argumentList)
        deferredThree = defer.Deferred()
        argumentList.append(deferredThree)
        deferredList.cancel()
        self.failureResultOf(deferredOne, defer.CancelledError)
        self.failureResultOf(deferredTwo, defer.CancelledError)
        self.assertNoResult(deferredThree)

        Cancelling a L{defer.DeferredList} will cancel the original
        L{defer.Deferred}s passed in.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_defer.py