<< return

Mocking GET requests with Python unittest.Mock

July 20, 2017

At the Mozilla All Hands, I finished getting all functional tests to work offline. Which means that I got everything to return fixture data and none of our API calls to ever go to an external website. But while in the All Hands I also realized that some tests from our Python unit tests were network dependant and needed to be mocked.

unittest.Mock

Our unit tests are written in Python, because our application is in Flask. So, to make them network independent I had to mock everything out in Python. That’s when I realized it was time to study and understand the Python unittest.Mock class. Because it provides us with a series of helper classes and methods to mock any function or object that you may need in a Python test.

In my case, I only needed to mock GET requests to the GitHub API. I had to patch the API call and return the expected data. In order to do that, understanding only one concept was key for me to know what I had to do: I only needed to patch the API call to GitHub, all the logic in the Webcompat application had to stay intact, or else I would be left with testing blind spots.

First I familiarized myself with the exact architecture of the webcompat application, to know which function I had to patch in order to only mock what was necessary. After doing that, it was very stright forward: patch the function and return the expected data from it.

Here is an example of one of the functions that I patched. Mind you, the function that made the API call is the webcompat.helpers.proxy_request:

def test_api_issues_out_of_range(self):
    '''API issue for a non existent number returns JSON 404.'''
    with patch('webcompat.helpers.proxy_request') as github_data:
        github_data.return_value = mock_api_response({
            'status_code': 404,
            'content': '[{"message":"Not Found","documentation_url":"https://developer.github.com/v3"}]'  # nopep8
        })
        rv = self.app.get('/api/issues/1', environ_base=headers)
        json_body = json.loads(rv.data)
        self.assertEqual(rv.status_code, 404)
        self.assertEqual(rv.content_type, 'application/json')
        self.assertEqual(json_body['status'], 404)

You can see that I don’t even need to return all the response that the GitHub API would, only the parts that I would need for everything to work right.

The illustration at the top was made by my good friend @onunes