Another example where a developer asks to call abort() to notice bugs, whereas Python previously silently ignored it: bpo-36829. Calling abort() is a legit use case, but not really the best default behavior. Again, the problem was solved by letting developers setting their own callback: sys.unraisablehook.

If I understood correctly, pytest doesn't override it but "took" into the default implementation: it chains its own code with the default implementation. It's possible because there is a way to "get" the current hook: just read sys.unraisablehook ;-)

Another argument in favor of also adding Py_GetThreadExitCallback() ;-)