The only case where I still invoke setup.py directly is "python setup.py test". I already knew it's deprecated, but don't understand what I'm supposed to do instead.

The article recommends tox, but how did tox get installed?

I can currently create and activate a new empty virtualenv, "pip install -U pip", clone and cd into my project, and run "python setup.py test". My test dependencies are automatically setup and my preferred runner (pytest) is used. If I change those in the future, the same commands will keep working because I am configuring those in setup.cfg, etc.

If I am now expected to manually "pip install tox" before testing my project and change that in the future if we start using something else, isn't that a step backward to the situation pyproject.toml et al were supposed to solve with needing to manually install specific stuff before using a project?