I think I might have said this before on another HN thread, but of course as an interviewer, I sometimes double-check the CVs and candidates to look for 'hidden qualities' such as open-source contributions. If one recruiter overlooks a candidate, I really ask them why and if the candidate DOES have significant and relevant patches, I actually bypass their decision and I bring them in onsite.
I find these technical programming tests useless for finding qualified candidates unless you are preparing for a programming olympiad or some other competitive programming competition. But open-source contributions allows me to find the patches you made on code reviewing tickets and see it in the open.
It would be better if more companies used open-source contributions as acceptable evidence of relevant experience these days.