def test_sock_mask_key(self):
        """A WebSocketApp should forward the received mask_key function down
        to the actual socket.
        """

        def my_mask_key_func():
            return "\x00\x00\x00\x00"

        app = ws.WebSocketApp(
            "wss://api-pub.bitfinex.com/ws/1", get_mask_key=my_mask_key_func
        )

        # if numpy is installed, this assertion fail
        # Note: We can't use 'is' for comparing the functions directly, need to use 'id'.
        self.assertEqual(id(app.get_mask_key), id(my_mask_key_func))
A WebSocketApp should forward the received mask_key function down
        to the actual socket.
        
websocket/tests/test_app.py