Flake8 Mock plugin

Remember that a mock's job is to say, "You got it, boss" whenever anyone calls it. It will do real work, like raising an exception, when one of its convenience methods is called, like assert_called_once_with. But it won't do real work when you call a method that only resembles a convenience method, such as assert_called_once (no _with!). Sometimes developers may not notice that they are using a non-existent mock method, because they are not getting an output error telling them so. And for some reason they can also forget to verify that the test cases fail before writing implementation code.

This plugin checks for possible non-existent mock methods when you run flake8, the Python code checker.

Inspired by http://engineeringblog.yelp.com/2015/02/assert_called_once-threat-or-menace.html.

Installation

You can install or upgrade flake8-mock with these commands:

$ pip install flake8-mock
$ pip install --upgrade flake8-mock

List of non-existent methods checked

• assert_calls
• not_called
• called_once
• called_once_with

Plugin for Flake8

When both flake8 and flake8-mock are installed, the plugin is available in flake8:

$ flake8 --version
5.0.4 (flake8-mock: 0.4, ...)

Example output

Once you run flake8, you can have something like:

$ flake8 test_file.py
test_file.py:27:1: M001 assert_calls is a non-existent mock method.
test_file.py:28:1: M001 called_once_with is a non-existent mock method.
test_file.py:39:1: M001 not_called is a non-existent mock method.
test_file.py:40:1: M001 assert_called is a non-existent mock method.

Credits

• Alejandro Gabriel Pereira is the main author.
• Nejc Zupan (Niteo) provided the idea and proof-reading.

Collaborators

• John Vandenberg
• Tom Prince
• Gasper Vozel
• Bjørnar Myrheim

Changes

0.4 (05-12-2023)

• Fix compatibility with flake8 >= 5.0.0.

0.3 (09-10-2016)

• Don't warn on assert_not_called, assert_called or assert_called_once.
• Use ASCII only in README.rst

0.2 (12-16-2015)

• Add Python 3 compatibility.

0.1 (10-20-2015)

• First release.

0.1dev0 (10-19-2015)

• First dev release.