def test_value(self):
        """
        The value of the L{FlagConstant} which results from C{&} has all of the
        bits set which were set in both of the values of the two original
        constants.
        """
        readWrite = (self.FXF.READ | self.FXF.WRITE)
        writeAppend = (self.FXF.WRITE | self.FXF.APPEND)
        flag = readWrite & writeAppend
        self.assertEqual(self.FXF.WRITE.value, flag.value)

        The value of the L{FlagConstant} which results from C{&} has all of the
        bits set which were set in both of the values of the two original
        constants.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_constants.py