Thanks for the information on the concerns with the safety of splitting process runs into multiple cache entries. I would certainly be in favour of allow the user to declare that the tests in a certain directory have no side effects, so that it would be safe to split a single process result into multiple cache entries when running them. I guess another option would be to add the ability to declare that certain tests should be run with the pytest-testmon plugin. Maybe then the testmon cache could be leveraged in the same way as the mypy cache is leveraged in this PR: https://github.com/pantsbuild/pants/pull/16276.