Back when the game came out, there was benefit to doing them simply to learn the tracks and learn driving techniques (which, really, is all they should be for rather than how they were used in previous games).
Then there was a period of time where PD turned off the contact penalty, meaning any of the AI races you could shunt everyone for an easy win and making all of the overtaking tests useless. Then they turned that back on, but turned on SRF on, making all of the tests useless. With SRF on, other than to win cars and get trophies, there honestly is no point to doing the tests anymore.