Python: python setup.py test is deprecated

[FRidh]

Describe the bug
The test command of setuptools has been deprecated. Packages should stop using it, we should stop using it as a default checkPhase.

Additional context
The command is currently used as the default checkPhase. It was not uncommon that we had to set a custom checkPhase, typically pytest or nosetests. Now that the command is being deprecated/removed, we can expect more variation in commands to be used. Upstream does encourage the use of tox, although I think we should generally avoid it because it's a relatively heavy. (OK, not very heavy, but because it has Python deps we can't use it for core packages because of the DAG)

Related

• Deprecate the test command pypa/setuptools#1878
• Deprecate test command pypa/setuptools#1684
• https://discuss.python.org/t/proposal-for-tests-entry-point-in-pyproject-toml/2077

[wamserma]

From what I've seen (very subjective), most packages are moving to either tox or pytest (without tox). The choice should be detectable with a few checks in the default checkPhase. For all others we could omit a warning requesting customization of the checkPhase.

[jonringer]

the "setup.py test" command is only ran today if format = "setuptools"; is set, which is no longer the default since #254136.

I think we can close this, but I'll defer to @FRidh 's judgement