You start out with only access to the Level 1 Target Tests. In order to unlock more of them, you must beat Classic Mode on varying difficulties. The following list shows how to earn the other levels of Target Tests.
Level 1: Already Available
Level 2: Beat Classic Mode twice on Easy or once on Medium
Level 3: Beat Classic Mode twice on Medium or once on Hard
Level 4: Beat Classic Mode twice on Hard or once on Very Hard
Level 5: Beat Classic Mode twice on Very Hard or once on Intense
If you unlock a higher difficulty level, it will unlock the lower tests as well. For example, if you were to beat Classic Mode on Very Hard, it would unlock Levels 2-4 at the same time. Really the best thing to do here is keep improving your skills on Classic Mode and make sure to have a LOT of coins in store.
Every man dies, but few truly live. Live your life to its fullest, every day as if it were your last.