recommended pytest-runner in setup_requires means packages fail to install often

[graingert]

The recommendation to add pytest-runner to setup_requires means that all users of that package end up with an unnecessary pytest-runner package installed. This is bad because it bypasses pip hashes and --trusted-host

https://docs.pytest.org/en/latest/goodpractices.html#integrating-with-setuptools-python-setup-py-test-pytest-runner

MechanicalSoup/MechanicalSoup#224
rxcomm/pyaxo#26
jpadilla/pyjwt#179

[graingert]

Going foward it's probably better to recommend only the conditional requirement https://github.com/pytest-dev/pytest-runner#conditional-requirement

[Zac-HD]

I agree - that section should at least discuss the downsides of using pytest-runner.

IMO we should present the manual option first, then discuss how this bypasses standard packaging tools, advise against it for libraries, and finally point to pytest-runner as a quick way to set this up for applications that can afford the extra dependency and may want to use setup.py-based testing.