Last Thursday I learned about
pytest-mock at a local python meetup. The
presenter showed how he uses
pytest-mock for his work, and it was kinda eye
opening. I knew what mocking was, but I had not seen it in this context.
Watching him use
pytest-mock I realized that mocking was not as hard as I had
made it out to be. You can install
pytest-mock, use the mocker fixture, and
patch objects methods with what you want them to be.
pytest-mock is out on pypi and can be installed with pip.
python -m pip install pytest-mock
What I actually did
Sometimes I fall victim to making these posts nice and easy to follow. It takes more steps than just pip install, you need a place to practice in a nice sandbox. Here is how I make my sandboxes.
mkdir ~/git/learn-pytest-mock cd ~/git/learn-pytest-mock # well actually open a new tmux session there echo pytest-mock > requirements.txt # I copied in my .envrc, and ran direnv allow, which actually just made me a virtual env as follows python3 -m venv .venv --prompt $(basename $PWD) source .venv/bin/activate # now install pytest-mock pip install -r requirements.txt # make some tests to mock mkdir tests nvim tests/test_me.py
create a tests/test_me.py
I just wanted to do something that was worth mocking, the first thing that came
to mind was to do something that made a network call. Here I made a method
that uses requests to go get the content on my homepage, but changes it's
return behavior based on the
status_code of the request.
I want to mock out
requests to ensure that GoGetter can handle both
(http success) and
404 (http not found) status codes.
# tests/test_me.py import requests class GoGetter: """ The thing I am testing, this is usually imported into the test file, but defined here for simplicity. """ def get(self): """ Get the content of `https://waylonwalker.com` and return it as a string if successfull, or False if it's not found. """ r = requests.get("https://waylonwalker.com") if r.status_code == 200: return r.content if r.status_code == 404: return False class DummyRequester: def __init__(self, content, status_code): """ mock out content and status_code """ self.content = content self.status_code = status_code def __call__(self, url): """ The way I set this up GoGetter is going to call an instance of this class, so the easiest way to make it work was to implement __call__. """ self.url = url return self def test_success_get(mocker): """ Show that the GoGetter can handle successful calls. """ go_getter = GoGetter() # Use the mocker fixture to change how requests.get works while inside of test_success_get mocker.patch.object(requests, "get", DummyRequester("waylonwalker", 200)) assert "waylon" in go_getter.get() def test_failed_get(mocker): """ Show that the GoGetter can handle failed calls. """ go_getter = GoGetter() # Use the mocker fixture to change how requests.get works while inside of test_failed_get mocker.patch.object(requests, "get", DummyRequester("waylonwalker", 404)) assert go_getter.get() is False