Python3 Unittest Mocking Requests Module

Question

I am comfortable using dependancy injection with Java's Mockito library, but have little experience using Python3's unittest.mock module. I am trying to assert that the Request instance's prepare method gets called. However the test fails on the assertion self.assertTrue(mock_request.prepare.called). Can someone please advise me on how to get this test passing?

import requests import unittest from unittest import mock class Engine(object): def get(self, **kwargs): session = requests.Session() req = requests.Request('GET', 'http://www.google.com', params=kwargs).prepare() response = session.send(req, timeout=1) class TestEngine(unittest.TestCase): @mock.patch('requests.Session') @mock.patch('requests.Request') def test_get(self, mock_request, mock_session): e = Engine() e.get() self.assertTrue(mock_request.called) self.assertTrue(mock_request.prepare.called) if __name__ == '__main__': unittest.main()

Martijn Pieters · Accepted Answer · 2016-12-17 15:21:27Z

Your code never accesses prepare on Request directly. The method is accessed on the return value of a call to Request(), so test for that instead by using the Mock.return_value attribute:

self.assertTrue(mock_request.return_value.prepare.called)

When debugging mock issues, I find it helpful to print out the Mock.mock_calls attribute for the top-level mock object; for your test printing mock_request.mock_calls produces:

[call('GET', 'http://www.google.com', params={}), call().prepare()]

showing that call().prepare() was indeed accessed (and the result of a call() is usually accessible via the Mock.return_value attribute, as shown above).

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