def test_assertNoResultPropagatesSuccess(self):
        """
        When passed a L{Deferred} with no current result, which is then
        fired with a success result, L{SynchronousTestCase.assertNoResult}
        doesn't modify the result of the L{Deferred}.
        """
        d = Deferred()
        self.assertNoResult(d)
        d.callback(self.result)
        self.assertEqual(self.result, self.successResultOf(d))

        When passed a L{Deferred} with no current result, which is then
        fired with a success result, L{SynchronousTestCase.assertNoResult}
        doesn't modify the result of the L{Deferred}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_assertions.py