Prepare for tox v4

[altendky]

Alphas are being pre-released so may as well try them out somewhere.

Draft for:

• [ ] This is never to be merged. Rather, it is for testing the prereleases with the tox4 command. On release the command will return to just tox.
• [ ] ~~tox 4 being released~~
• [ ] ~~Removing the --pre for tox now that we know it (at least the alpha 5) works~~
  • Just specified 4 specifically (allowing alpha5+)

[codecov[bot]]

Codecov Report

Merging #319 (156ee84) into master (7f20910) will not change coverage. The diff coverage is n/a.

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  Coverage   96.78%   96.78%           
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  Lines        1183     1183           
  Branches      106      106           
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  Hits         1145     1145           
  Misses         20       20           
  Partials       18       18           

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[altendky]

I expect various people won't really like this. If you are reviewing and you just don't like it, don't worry too much. Just feedback on how you think this situation ought to be handled is a start I would appreciate.

The basic issue is that despite the non-CI bit of the project requiring no changes to work with tox v4, the CI bit does need to reference the command tox4 when it gets that version and tox when it doesn't (so long as we continue to support Python <3.6 since tox v4 is py3.6+). Once you are referring to one command or the other you also need to be sure you are installing the version that will provide that command. I guess the version could be handled as 'tox~=3.0; python_version < "3.6"' 'tox~=4.0a5; python_version >= "3.6"'. I'm not sure that is better though since the other selection mechanism has to stick around to identify which command to run and doing both bits the same way seems simpler.

[altendky]

https://discuss.python.org/t/tool-tox-4-on-the-horizon/6537/3

While it becomes stable it installs under the tox4 console entry and uses the tox4 working directory (not to break v3).

Ok, so apparently this is mostly pointless and probably shouldn't be merged. Sorry for the noise. I'll keep this around and run it every now and again to keep checking against tox 4. But, at some point the command will return to just tox and none of this will be needed.

[hynek]

We've switched to nox for now, so closing.