human
Solve the following python programming problem given the following code:
@ pytest.fixture 
def mock_message() : 
    base_msg = { 
        'id' : '1234', 
        'subject' : 'Test Message', 
        'account_id' : MOCK_ACCOUNT_ID, 
        'object' : 'message', 
        'labels' : [{ 
            'name' : 'inbox', 
            'display_name' : 'Inbox', 
            'id' : 'abcd', 
}], 
        'starred' : False, 
        'unread' : True, 
} 
    response_body = json.dumps (base_msg) 
    def request_callback(request) : 
        payload = json.loads (request.body) 
        if ('labels' in payload) : 
            labels = [{ 
                'name' : 'test', 
                'display_name' : 'test', 
                'id' : l, 
} for l in payload ['labels']] 
            base_msg ['labels'] = labels 
return (200, { 
            
}, json.dumps (base_msg)) 
endpoint = re.compile ((API_URL + '/messages/1234')) 
    responses.add (responses.GET, endpoint, content_type = 'application/json', status = 200, body = response_body) 
    responses.add_callback (responses.PUT, base_msg, content_type = 'application/json', callback = request_callback) 

    
    

    Fix the buggy line: responses.add_callback (responses.PUT, base_msg, content_type = 'application/json', callback = request_callback)
assistant
#Here is Python code to fix the buggy line: responses.

responses.add_callback (responses.PUT, endpoint, content_type = 'application/json', callback = request_callback)