In Gran Turismo 5, like in previous versions, you unlock license tests by completing various different tasks in the game. Here is the list of license tests you’ll unlock, and the order you’ll unlock them in.
B License Tests – Purchase your first car
A License Tests – Reach level three and complete the B License Tests
International C License Tests – Reach level six and complete the A license tests
International B License Tests – Reach level nine and complete the International C License Tests
International A License Tests – Reach level twelve and complete the International B License Tests
S License Tests – Reach level 15 and complete the International A License Tests