def test_failureValueFromFailure(self):
        """
        A L{failure.Failure} constructed from another
        L{failure.Failure} instance, has its C{value} property set to
        the value of that L{failure.Failure} instance.
        """
        exception = ValueError()
        f1 = failure.Failure(exception)
        f2 = failure.Failure(f1)
        self.assertIs(f2.value, exception)

        A L{failure.Failure} constructed from another
        L{failure.Failure} instance, has its C{value} property set to
        the value of that L{failure.Failure} instance.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_failure.py