Parallelize the test suite

[woodruffw]

From conversation wit @miketheman: the tests do currently parallelize cleanly, but coverage is broken in the process. My SWAG explanation is that coverage's intermediate files may be generated with the same seed in each process, resulting in clobbered outputs.

WIP branch from above: https://github.com/pypi/warehouse/compare/main...miketheman:miketheman/pytest-xdist?expand=1

I've asked @DarkaMaul to take a look at this once his queue is empty 🙂

[DarkaMaul]

Hi all - I've spent some time analyzing this issue.

I managed to find a solution to improve the coverage report using sitecustomize.py.

The idea is borrowed from coverage documentation and is also used by pytest-cov plugin : here

My work-in-progress is available here

I get about 99% coverage, with the following report
A progress, but still not complete.

Edit: I overlooked the regex used in the .coveragerc file and now the coverage is complete:

+ python -m coverage report -m --fail-under 100
Name    Stmts   Miss Branch BrPart  Cover   Missing
---------------------------------------------------
TOTAL   14394      0   4572      0   100%