You should keep a savegame (or memory card, depending on what you're playing on) with all the license tests you made and just copy and rename it every time you desire to start a new game... I do this.
There's the gameshark alternative: I know the exhistence of codes which basically give you all the license test with gold ranking in a row, but I never tested them, anyway a quick Google search for "GT2 gameshark codes - all gold licenses" should do the trick.