You will need to speak with the dealership or car owner of the car that you are test driving to find out if their insurance will cover you operating the vehicle. Likely it will but you will want to make sure since if not then you may be personally responsible for damages if you are in an accident since this typically would not be covered under your own insurance policy.

Test driving a car should be covered under the used or new car dealer's policy or a private owner's car insurance policy.

Most dealers will have full insurance coverage, which is called a garage policy. If you sign something accepting responsibility for damage then you would be responsible for that damage. It is up to you to accept, or reject the offer of a test drive based on your knowledge of potential liability if you are in a collision.