def test_add(self):
        """
        Addition is as expected in this space, for example: 255+1 == 0,
        100+100 == 200, and 200+100 == 44.
        """
        self.assertEqual(
            serialNumber8(255) + serialNumber8(1), serialNumber8(0))
        self.assertEqual(
            serialNumber8(100) + serialNumber8(100), serialNumber8(200))
        self.assertEqual(
            serialNumber8(200) + serialNumber8(100), serialNumber8(44))

        Addition is as expected in this space, for example: 255+1 == 0,
        100+100 == 200, and 200+100 == 44.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_rfc1982.py