profile| Adds (opt-inable) profile-heatmap generation output to tox test-runs

[doublethefish]

Steps

• Add yourself to CONTRIBUTORS if you are a new contributor.
• (n/a) Add a ChangeLog entry describing what your PR does.
• (n/a) If it's a new feature or an important bug fix, add a What's New entry in doc/whatsnew/<current release.rst>.
• Write a good description on what the PR does.

Description

Fairly straight-forward change enabling the creation heatgraphs for test-runs, when and as needed.

We can use tox -epy38 -- --profile-svg to enable this functionality now that we have the pytest-profiling dependency added to tox.

Partly addresses #1954. Split out from the original PR for #3473.

Type of Changes

	Type
✓	🔨 Refactoring

Related Issue

[coveralls]

Coverage remained the same at 90.454% when pulling 6208861 on doublethefish:profile/heatmaps_for_testruns into 67d0572 on PyCQA:master.

[coveralls]

Coverage remained the same at 90.442% when pulling 1e21a0d on doublethefish:profile/heatmaps_for_testruns into 0ea3410 on PyCQA:master.

[PCManticore]

Thanks for the PR. I think this should be either a separate step or controlled via an additional parameter (which we can already pass via posargs). The reason is that running the test suite locally already takes a bit for contributors, but slowing it down wholesale would not make a lot of sense if folks don't work on performance related patches.

[doublethefish]

I very much agree.

How does the 'postargs' option work? I've not been able to use it for stuff like this, passing --profile-svg or test-paths to tox and I've not found the docs very useful. If we can add an arg switch to enable it for the test-runs that would be ideal as being able to get perf info for the tests is really useful.

Adding a new step means code-duplication, which will make the tox config more complex and I feel that we should also avoid that. What I suggest is just taking PR #3498 for now and if we can get post-args to work for this later then do so.

Edit: I reread the tox docs and updated the description. This a much more maintainable patch now IMO

[PCManticore]

Nice, thanks a lot!