You will need to check with the Department of Public Safety or TX Drivers License office to find out for certain what proof of insurance you need for the car you will be operating for the driving test. If you are driving your mother’s car than likely her insurance company would require you to be added to the policy in order for you to be covered while driving her car for the test and at other times.

According to the Texas Department of Insurance, young drivers must comply with the state's financial responsibility laws, just as older drivers do. Most young drivers, however, have the option of satisfying their legal requirements by being added to their parents' auto policy. Adding a young driver to a parents' policy can be expensive, but it's cheaper than taking out a separate auto policy.

The TX DOI site goes on to say that a parents' policy covers children living at home or away at school, even when not named on the policy. Even though children are automatically covered on their parents' policy, it's important that they be listed on the policy as soon as they reach driving age.

Insurance companies are required to charge the correct rate, based on the classifications of the drivers in your family. If the parents don't have all of the drivers in their family listed on their policy and the insurance company learns about them later - because of an accident claim, for instance - the company will bill the policyholder for the extra premium you should have paid.