In California, you do not necessarily need to have your name listed on your parents' insurance policy to take the behind-the-wheel driver's test using your grandma's car, which is already covered under their policy. Insurance companies typically require all licensed drivers in a household to be listed on the auto insurance policy, except for unlicensed teenagers or younger members under 14. However, this requirement is primarily for those who live in the household and drive the car regularly. If you are only borrowing your grandma's car occasionally for the driving test and do not live with your parents, you may not need to be listed on their policy.
However, to be on the safe side, it's essential to have a comprehensive auto policy that covers everyone who drives in your household, including those who don't live with you but drive your car occasionally. In this case, since your grandma's car is already covered under your parents' policy, you should verify with their insurance company that you are covered to drive the car for the driving test. You may also want to confirm with the DMV that you meet their requirements for insurance coverage. It's essential to have proof of insurance when taking the driving test, and you may need to provide this documentation at the testing site. Additionally, it's worth noting that if you are the registered owner of the car, you will need to purchase your own auto insurance policy under your own name, even if your parents are co-owners and you still reside with them. This is because insurance companies typically write checks to the registered owner in case of an accident.