You can do tests which are offline practice, however you still need the internet to use the iracing website. In the test session you can use any car/track combination. You can also do practice sessions online where you can drive with other people on the car/track set for the season's schedule during that week. Even though you're online with other people, SR and iRating do not count in the practice sessions, so it's a great place to practice close driving with other people without having to worry about being punished!