如何在单元测试中使用python Mock side_effect作为Class方法

Question

I am testing a custom API in python that makes http requests, but I don't want to make a request to the real external system every time I run the unit tests. I am using python's mock library with a side_effect function to dynamically fake the API response. How do I get the side_effect method to behave like a class method?

import requests

class MyApiClass():
    def make_request(self, params):
        return requests.get('http://someurl.com', params=params)

    def create_an_object(self, params):
        return self.make_request(params)

---

import unittest, mock

def side_effect_func(self, params):
    if params['name'] == 'Specific Name':
        return {'text': 'Specific Action'}
    else:
        return {'text': 'General Action'}

class MyApiTest(unittest.TestCase):
    def setUp(self):
        super(MyApiTest, self).setUp()
        mocked_method = mock.Mock(side_effect=side_effect_func)
        MyApiClass.make_request = mocked_method

    def test_create_object(self):
        api = MyApiClass()
        params = {'name': 'Specific Name'}
        r = api.create_an_object(params) # Complains that two arguments are needed!
        self.assertEqual(r['text'], 'Specific Action')

---

I get this error

TypeError: side_effect_func() takes exactly 2 arguments (1 given)

but I want side_effect_func to pass api as the first argument. Appreciate any help!

Answer 1

The simplest way would probably be to just make your mock method take a single argument, then reference MyApiClass statically within the mock method itself. Otherwise, you could try mocking the class object itself (basically making a mock metaclass) or maybe using a factory that utilizes partial to build a mock class method on the fly. But if the single argument/static reference method would work for you, that seems the best to me.

Also, from the Mock docs, there's mocking an unbound method using patch , which looks like it may be more what you need.