After looking at the test results, the doctor (and perhaps some other specialists) may conclude that the person has a medical or psychological condition that causes events that look like epilepsy seizures. In that case, treating that condition (instead of giving seizure medicines) may prevent future incidents.
On the other hand, all the test results might be normal. Then the doctor has to determine whether treatment is needed. Some people have a single seizure and don't have any more. But others go on to have more seizures later, leading to the diagnosis of epilepsy.