How to use mock in request.post to an external api

Question

I tried reading some of the things regarding unittest.mock but I couldn't grasp it so maybe using my use case will help me learn more about this.

Basically I have this function that calls an external api:

# service.py
def create_user(name):
    headers = {
        ...
    }
    url = external.URL + 'user/'
    payload = {
        "name": name
    }
    response = requests.post(url, headers=headers, data=json.dumps(payload))

    return response.json()

so I'm trying to create a test but I'm not sure how to use unittest.mock for this function. I could test this function directly but I want to learn more about mocking and why should I do it. Sorry if this question has been asked many times but I really want to understand it with my use case.

Answer 1

You could use patch.object to mock requests.post method.

Eg

service.py :

import json
import requests
from collections import namedtuple

external = namedtuple('URL', 'URL')
external = external('http://localhost:3000/api/')


def create_user(name):
    headers = {}
    url = external.URL + 'user/'
    payload = {
        "name": name
    }
    response = requests.post(url, headers=headers, data=json.dumps(payload))

    return response.json()

test_service.py :

import unittest
import requests
from service import create_user
from unittest.mock import patch, Mock
import json


class TestService(unittest.TestCase):
    @patch.object(requests, 'post')
    def test_create_user(self, mock_post):
        mock_json = Mock()
        mock_json.return_value = 'mock data'
        mock_post.return_value.json = mock_json
        actual = create_user("teresa teng")
        mock_post.assert_called_with('http://localhost:3000/api/user/', headers={},
                                     data=json.dumps({"name": "teresa teng"}))
        self.assertEqual(actual, 'mock data')


if __name__ == '__main__':
    unittest.main()

unit test result with coverage report:

coverage run /Users/ldu020/workspace/github.com/mrdulin/python-codelab/src/stackoverflow/63899742/test_service.py && coverage report -m --include="src/*"
.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK
Name                                         Stmts   Miss  Cover   Missing
--------------------------------------------------------------------------
src/stackoverflow/63899742/service.py           11      0   100%
src/stackoverflow/63899742/test_service.py      15      0   100%
--------------------------------------------------------------------------
TOTAL                                           26      0   100%