Switch to tox

[lbdreyer]

WIP This is now ready for review

This switches our use of nox to tox, re #4806

[lbdreyer]

So this should be all good to go, but there are now three test failures:

FAILED lib/iris/tests/unit/analysis/stats/test_pearsonr.py::Test::test_perfect_corr
FAILED lib/iris/tests/integration/plot/test_vector_plots.py::TestBarbs::test_2d_plain_latlon
FAILED lib/iris/tests/integration/plot/test_vector_plots.py::TestBarbs::test_2d_plain_latlon_on_polar_map
==== 3 failed, 6767 passed, 36 skipped, 15220 warnings in 178.70s (0:02:58) ====

Which is interesting since I've not touched any test files. Maybe something to do with the environment creation!

[trexfeathers]

This is coming together nicely! Couple of final observations.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5b42f47) 89.37% compared to head (fba88d7) 89.37%.
Report is 184 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5184   +/-   ##
=======================================
  Coverage   89.37%   89.37%           
=======================================
  Files          89       89           
  Lines       22426    22426           
  Branches     5379     5379           
=======================================
  Hits        20043    20043           
  Misses       1637     1637           
  Partials      746      746           

☔ View full report in Codecov by Sentry.
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[lbdreyer]

This is getting closer. I just have to make change to the benchmarks and test them locally.

[lbdreyer]

Benchmarks ran, so this should now be ready!

[trexfeathers]

Since everything is in a single commit I think I'll need to go back through all the changes - I can't remember which bits I did and didn't review back in March.

So this will need to wait until after the sprint.

[lbdreyer]

Thanks! no rush at all!

[trexfeathers]

OK, I've been through this with fresh eyes, including lots of trial tox runs locally, and I think it makes sense. The Tox world seems a lot slicker than the Nox world, even if I did need to learn a new syntax 👍

So my only outstanding caution is concerning dependency on tox-conda, since it's such a small project. See below.

[trexfeathers]

I feel a little uncomfortable that this remains necessary over 6 months later (see tox-dev/tox-conda#163).

tox-conda looks in need of more maintainers, are we comfortable being dependent on it? @lbdreyer @bjlittle

[trexfeathers]

Do we need Nox OR Tox anymore, now that we use lock files?!

[trexfeathers]

Do we need Nox OR Tox anymore, now that we use lock files?!

Having thought more, that was ill-informed, since Tox still offers neat inheritance tricks. But if we stick with tox-conda, we need to be comfortable sticking with the pin as well. Of course being pinned kinda undermines the idea of adopting something more popular.

Thanks @ESadek-MO and @HGWright for conversation on this topic.

[trexfeathers]

Also leaves us to potential security vulnerabilities:

tox-dev/tox#2524 (comment)

[trexfeathers]

Looks like this didn't get recorded, but discussions between @SciTools/peloton in December concluded that we should investigate how easy it would be to maintain our own tox-conda plugin, with just the features that we need. @pp-mo expressed an interest in this, I don't know how it has progressed.

We accepted that this is less good than maintaining the real, public plugin. But we also agreed that it could be the pragmatic approach since a private plugin would take less maintenance and make us less vulnerable to outside forces.

@HGWright highlighted that if we got a proof-of-concept together then we could potentially start a conversation on the tox-conda repo to see how many others are maintaining their own plugin and discuss pooling resources.

This matters for this PR, as I am increasingly reluctant to approve tox-conda becoming a dependency.

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