There are many points. The tests help to:
1. Accustom you to new physics.
2. Increase A-Spec Experience to drive higher tier cars in higher tier race series.
3. Give you prize cars to sell or use at your discretion.
4. Lets (forces) you test-drive a variety of Premium cars.
5. Lets (forces) you to test-drive sections and full laps of new courses.
6. Lets you purchase a new DS3 controller or wheel, because you threw it through your television.
7. You'll need to buy a new television.
...and the list goes on. Hope that helps.
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