def test_mutualExclusionPrimeDirective(self):
        """
        L{mutuallyExclusiveArguments} does not interfere in its
        decoratee's operation, either its receipt of arguments or its return
        value.
        """
        @_mutuallyExclusiveArguments([('a', 'b')])
        def func(x, y, a=3, b=4):
            return x + y + a + b

        self.assertEqual(func(1, 2), 10)
        self.assertEqual(func(1, 2, 7), 14)
        self.assertEqual(func(1, 2, b=7), 13)

        L{mutuallyExclusiveArguments} does not interfere in its
        decoratee's operation, either its receipt of arguments or its return
        value.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_deprecate.py