Test Python development versions in GitHub Actions

[pquentin]

This is actually different from Travis as we're not testing nightly builds, but alpha versions. Should we use the deadsnakes nightly builds instead?

Also, 3.10 does not work yet, due to benjaminp/six#341.

[codecov]

Codecov Report

Merging #1827 (e5d9c42) into master (1538327) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1827   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files         114      114           
  Lines       14503    14503           
  Branches     1105     1105           
=======================================
  Hits        14451    14451           
  Misses         37       37           
  Partials       15       15           

[njsmith]

I think for 3.x versions that have already been released, we want the nightlies? I don't think there are alphas/etc. for 3.x.y point releases, after 3.x.0 comes out.

For the next release, 3.10 currently, I guess alphas/betas/rcs do have some argument in their favor -- in particular, they might reduce the frequency of weird breakage. But if we have to edit the .yml every time a new alpha comes out, we aren't going to do it, so we'll end up not actually testing the new versions... not sure if there's any way to avoid that.

[altendky]

I don't know anything about nightlies but if I did my testing right (I don't recall in detail) then this will progress from alphas through release anyways.

https://github.com/pytest-dev/pytest-twisted/blob/8a955b66bb22c0e2f09fc5cdaed241dd93e53a75/.github/workflows/ci.yml#L146

        uses: actions/setup-python@v2
        with:
          python-version: '${{ matrix.python.action }}.0-alpha - ${{ matrix.python.action }}.X'
          architecture: x64

[njsmith]

Regardless of what we end up doing for 3.10, this looks like a definite improvement over what we have now. I would hit merge now, but it looks like merging is currently blocked though because some rc.2 builds are expected but missing? I could go disable them but I'm not quite sure what's going on so I'd be more comfortable delegating that to @pquentin, assuming your the one who was in the middle of changing them and knows what the current status is :-)

[pquentin]

Right I also have a unrelated commit where I change 3.9.0-rc.2 to 3.9. Sorry I'm currently on holidays and have limited time to fix this. Feel free to take over.

[njsmith]

Right then, let's do it. (And @pquentin, hope you had/are having a great holiday :-))