It will depend on the company.

Typically, all residents of a household need to be listed or excluded ona policy. Immediate roommates who are non-family and do not drive the vehicle may not need to be included with most companies. Some companies might make you list your roommates (if you have just a few you actually room with) and then exclude them from the policy. To be certain you should check with your insurance agent to determine if your friend would be covered.

If they are listed on your policy then they would be covered, if they are excluded on your policy then they would not be covered. If you notified the company about them and they are neither listed nor excluded then the company should cover them - if they were disclosed.

You can comparison shop your policy here by getting a car insurance quote.