Good question. Thanks for asking. I thought about this too.

The doctests are not run as part of the test suite. Perhaps that's something worth pursuing, but not something I've yet invested time or energy on. Since I'm the primary or sole maintainer on these projects that are preferably developed upstream in the third-party repos, I'm comfortable relying on the doctests, but you're absolutely right that it's a risk. There are other tests too, like "test_complexity" that exist only in the third-party repo (due to the dependency on other third-party packages to perform the tests).

I had thought that the //two-slash.txt was still part of the unit test, but I see now, looking at the diff, that it is indeed missing. Looking at the same test in zipp, the lines are still present, so I need to assess where those lines went missing.