I have hired employees via the HR system and also have bypassed HR when needed. In all cases, it was left up to the managers/supervisors to test the candidates' knowledge.
I've never known HR to make the hiring decisions. They just use the criteria prepared by the managers/supervisors to separare the wheat from the chafe and make sure that everyone who gets an interview at least meets the minimum requirements.
But the final hiring decision is never made by HR.