Split tests into groups for parallel execution in CI/CD runners

[billschereriii]

Split tests into groups for parallel execution in CI/CD runners
Remove some unused import statements

[codecov]

Codecov Report

Merging #417 (969ecc5) into develop (96765d9) will increase coverage by 0.05%.
The diff coverage is n/a.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #417      +/-   ##
===========================================
+ Coverage    89.60%   89.65%   +0.05%     
===========================================
  Files           59       59              
  Lines         3617     3617              
===========================================
+ Hits          3241     3243       +2     
+ Misses         376      374       -2     

see 1 file with indirect coverage changes

[al-rigazzi]

I like the divide-and-conquer approach. Nevertheless, the probability of hitting the pre-existing issue with Codecov is multiplied by a factor of ~3, thus I'd suggest we decide whether we are going to mark as passed the action even if codecov failed and, if that's the case, we do it as part of this PR.

[billschereriii]

Looks like all the tests ran in between 9 to 18 minutes, btw

[billschereriii]

Note: subdirectories full_wlm and on_wlm are intentionally skipped for CI/CD as we aren't running on HPC systems for these tests

[ankona]

Per @al-rigazzi comment about codecov... Do we want to do a minor rearrange of the build to avoid 3x the uploads? Perhaps we could:

1. run independent test step
2. store each codecov report as an artifact in a test step
3. split code coverage upload to run into step successor of (1)
4. retrieve all artifacts and upload only one time

The key difference in my head is to pull all artifacts instead of look for ./coverage.xml (and to figure out how to make the step depend on each matrix-based step).

[ankona]

LGTM. Approving & assuming you'll want to split out anything about rearranging to upload codecov results fewer times into a new ticket.

[ankona]

Other than the opaque group names, this is simple & effective. LGTM as the first step toward test domination!