The test_socket patch is incomplete with the way I've been converting test modules, but it is a good starting point.  Should this issue be renamed to be specifically for test_socket?

The necessity of reaping threads at the end of the test poses a bit of an issue for test discovery, which has been discussed pretty thoroughly in #16968.  If the fix in that issue is approved and committed, it would be pretty easy to extend Matt's test_socket patch to complete the conversion.