It actually depends! Depending on the amount of time you have to prep, you may need all 7 or you may only need 4. We recommend taking a practice test every 2-3 weeks. So if you have 6 months to prep, you can study slowly and try to get in all practice tests. But if you only have 2 months, you might get in 3-4.
Our recommendation is to spend 3-4 months prepping and take a test every 2-3 weeks.