def test_failureValueFromFoundFailure(self):
        """
        A L{failure.Failure} constructed without a C{exc_value}
        argument, will search for an "original" C{Failure}, and if
        found, its value will be used as the value for the new
        C{Failure}.
        """
        exception = ValueError()
        f1 = failure.Failure(exception)
        try:
            f1.trap(OverflowError)
        except:
            f2 = failure.Failure()

        self.assertIs(f2.value, exception)

        A L{failure.Failure} constructed without a C{exc_value}
        argument, will search for an "original" C{Failure}, and if
        found, its value will be used as the value for the new
        C{Failure}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_failure.py