def test_maybeDeferredAsync(self):
        """
        L{defer.maybeDeferred} should let L{defer.Deferred} instance pass by
        so that original result is the same.
        """
        d = defer.Deferred()
        d2 = defer.maybeDeferred(lambda: d)
        d.callback('Success')
        result = []
        d2.addCallback(result.append)
        self.assertEqual(result, ['Success'])

        L{defer.maybeDeferred} should let L{defer.Deferred} instance pass by
        so that original result is the same.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_defer.py