The sys.monitoring and import optimisation suggestions apply as-is.

If you use standard unittest discovery the third item might apply as well, though probably not to the same degree.

I don’t think unittest has any support for distribution so the xdist stuff is a no.

On the other hand you could use unit test as the API with Pytest as your test runner. Then you can also use xdist. And eventually migrate to the Pytest test api because it’s so much better.

I profiled a huge legacy tests collection using cProfile, and found lots of low hanging fruits. Like some tests were creating 4000x3000 Pillow image in memory just to test how image saving code works (checkign that filename and extension are correct). And hundreds of tests had created this huge image for every test (in the setUp method) because of unittest reliance on inheritance. Reducing size image to 10x5 made the test suite faster for like 5-7% (it was long time ago, so I don't remember exact statistics).

So, I'd run the tests under cProfile first.