I suspect a large number of magi just judge for themselves if their apprentice is fully trained, rather than resorting to a so-called 'gauntlet'. After all, the last few years of apprenticeship is generally when they are taught spells, and that's got to give the master an idea of where their apprentice is sitting, arts and Magic Theory wise. Mostly these gauntlets are about the master showing off more than whether or not their apprentice is 'worthy'.
This isn't to say that a master might not 'test' an apprentice (at any point in their apprenticeship, not just the end), but I suspect tests of character would be more common than tests of ability.YMMV.
EDIT: Probably wasn't clear enough...many masters setting gauntlets will want to show off their apprentice in a public fashion, rather than doing super-secret hush-hush stuff. Gauntlets should be showy.