Python manage.py pytest or Making Django Use Pytest

Posted on Sat 18 April 2020 in Posts

Edit: For those who prefer visual content, I've recorded this as a video on Youtube which you can find at: https://youtu.be/toKW2YLnGFQ

Ok, so I've had to convert some Django projects to use Pytest as the test runner rather than the built in one that Django uses. This is actually pretty straightforward, and I even recorded a Youtube video showing the process.

That's all fine and good, but one of the complaints I've heard from Django-ista's (is that a term? Djangoites? Django Devotees?) is that it means now the good old normal python manage.py test no longer works (well, I suppose technically it still works, but doesn't use Pytest).

So challenge accepted, as one can certainly create custom manage.py commands in Django, so lets create a custom management command to run our unit tests with Pytest instead of the default built-in runner.

Python Manage.py pytest

So first challenge is "how do we run pytest from Python?" as normally you run Pytest as a command line tool. As it turns out there's docs on how to do this on Pytest's site.

The trick is to import pytest and then call pytest.main() passing in the same command line arguments you'd give to Pytest in the terminal to that function. As an example:

pytest.main(['--lf'])

Would be the same thing as doing pytest --lf on the command-line. Easy peasy. So started a basic custom management command in a file called pytest.py and put it into my Django project's management/commands directory.

import pytest
from django.core.management.base import BaseCommand


class Command(BaseCommand):
    help = "Runs tests with Pytest"

    def handle(self, *args, **options):
        pytest.main()

This works, in that now I can do python manage.py pytest and it'll run Pytest as if I just ran the pytest executable in the current directory.

Cool, but how do I start passing arguments? Normally in a custom Django management command you define a add_arguments function and use the argparse module to define the expected arguments for your custom command. In this case though, I essentially want the interface to Pytest, which would be non-trivial to recreate by hand (there's a lot of options on that Pytest executable).

But, with argparse, there is a way to essentially say "accept any arguments", and that's the argparse.REMAINDER value for the nargs parameter (docs).

argparse.REMAINDER. All the remaining command-line arguments are gathered into a list. This is commonly useful for command line utilities that dispatch to other command line utilities

Perfect, that's exactly what I want. Adding to our management command is straighforward:

import argparse

import pytest
from django.core.management.base import BaseCommand


class Command(BaseCommand):
    help = "Runs tests with Pytest"

    def add_arguments(self, parser):
        parser.add_argument("args", nargs=argparse.REMAINDER)

    def handle(self, *args, **options):
        pytest.main(list(args))

Now whatever arguments we pass to our manage.py pytest command will be passed directly through to the pytest.main function. Exactly what I want, and super concise.

But That's Still Different

At this point it worked, but I could still hear those nagging voices saying, "yeah but manage.py pytest is not the same as manage.py test". Fine, as it turns out though you can override any of the built-in manage.py commands.

The trick is to just create a custom management command with the name of the command you want to override, and make sure your app is the last one in Django's INSTALLED_APPS setting. So in our case we could just rename our management/pytest.py file to management/test.py and it'd work. But I kinda liked having both (ie both manage.py pytest and manage.py test being effectively an alias to it). So I created a management/test.py file and put in the following:

# Override the built in Django manage.py test with pytest
from djangotest.management.commands.pytest import Command

Yup, that's it, 1 line of code. Now doing a python manage.py test runs Pytest as the test runner.

Did this all on a test project, source is up on Github at: https://github.com/pzelnip/djangotest

Or if you just want to see the management commands, they're at: https://github.com/pzelnip/djangotest/tree/master/djangotest/management/commands