Add docs on how to run tests

[aduh95]

I couldn't find docs on how to run tests locally, so I had to take a few guesses. I'm suggesting a section at the end of the README.

[cclauss]

I think this can all be replaced with pip install --editable . which is a pytest best practice.

• https://docs.pytest.org/en/stable/explanation/goodpractices.html?highlight=pip+install+-e+.

Or more compactly as demonstrated in the GitHub Action pip install --editable ".[dev]"

[cclauss]

This is not required if you have a venv.

[aduh95]

Does it hurt though? If not, it seems to me better to keep it.

[cclauss]

Yes. It hurts. Please read Why do virtual environments exist? from a long-term core Python developer and head of Python development for VSCode... https://snarky.ca/how-virtual-environments-work

[aduh95]

In the end, whether you type python after activation or .venv/bin/python makes no difference to Python

Hum I don't know if I'm reading that right, but it seems to me this implies it would not hurt, as it says it makes no difference, no? 🤔

[cclauss]

It says that the goal of using a virtualenv to avoid installing your dependencies into your system Python.
Doing so can cause dependency conflicts that can become unresolvable when multiple projects are installed.

[aduh95]

Yes, I do see the upsides of using a virtualenv, much less troublesome than spawning a docker container. But I thought you were saying “it hurts to use sys.executable instead of "python"”, and – I guess this where I’m missing something – I don’t see how that relates to virtualenv or how it would hurt.

[cclauss]

This is not required if you have a venv.

[cclauss]

The reason for the shift to sys.executable is to enable skipping the best practice of making a venv (which links python to python3 in Linux and macOS and to py in Windows). Let's reenforce the use of the best practice in our instructions.