human
Solve the following python programming problem given the following code:
@ mock.patch ('tornado.ioloop.PeriodicCallback') 
def test_publisher_initializer(self, periodic_callback_mock) : 
    'Test instrument_ioloop() setups monitoring and creates a PeriodicCallback' 
    def publisher() : 
        pass 
result = initialize_mutornadomon (io_loop = tornado.ioloop.IOLoop.current (), publisher = publisher) 
    assert <MASK>.called 
    self.assertTrue (isinstance (result, mutornadomon.MuTornadoMon)) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
periodic_callback_mock