There are two main things to consider if you plan on borrowing a car for your driving test: insurance and permission.
Insurance follows the car; as long as the vehicle has insurance and you have proof of that insurance, you will most likely be covered in the event of an accident. Make sure you have the insurance ID card with you for the road test.
Also, you need to have permission to use the vehicle from the named insured. If, at the time of loss, it’s discovered that the vehicle was taken without the owner’s knowledge and without permissive use, an accident won’t be covered.