Using uv.lock file in tox

I’ve migrated all my open source packages to uv a while back, and the ones which are Django packages are using tox to run the tests against all supported combination of Django + Python versions.

However, I didn’t realise that the tox-uv plugin does not install dependencies from the uv lockfile by default.

The realisation came in the django-money project: the test were running fine despite the lockfile being out of date.

This is explicitly documented on the tox plugin project, but I completely missed that, and assumed it would just magically work.

The fix I suggested is heavily inspired by Adam Johnson’s setup (example from django-cors-headers). When I don’t know how to do something in Django 3rd party packages, I often check one of his packages and always learn something from it.

Here are the key points:

1. Add runner = uv-venv-lock-runner to the tox test envs
2. Move the Django versions from tox.ini to pyproject.toml in dependency-groups and replace them by dependency groups
3. Add tool.uv.conflicts to mark the dependency groups as incompatible for uv (documentation)

That’s it! Once again, thanks Adam!