def test_findFailure(self):
        """
        Within an exception handler, it should be possible to find the
        original Failure that caused the current exception (if it was
        caused by raiseException).
        """
        f = getDivisionFailure()
        f.cleanFailure()
        try:
            f.raiseException()
        except:
            self.assertEqual(failure.Failure._findFailure(), f)
        else:
            self.fail("No exception raised from raiseException!?")

        Within an exception handler, it should be possible to find the
        original Failure that caused the current exception (if it was
        caused by raiseException).
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_failure.py