Tests for epilepsy
BMJ Group Medical Reference
Doctors will do lots of tests to find out whether your seizures are caused by epilepsy. However, the tests aren't perfect, and may not be able to tell you for certain whether you have epilepsy. Here's a brief description of the tests you or your child may have. Electroencephalogram (EEG)
An electroencephalogram (EEG) measures the amount of electrical activity in the nerve cells of your brain. An EEG can tell your doctor: 
If the electrical activity in your brain is normal
Where in your brain any abnormal activity starts
What type of seizure you or your child may be having and what sort of epilepsy might be causing it.
Guidelines from the National Institute for Health and Clinical Excellence (NICE), the government body that advises doctors about tests and treatments, say that if you need this test, you should have it within four weeks. 
The test can't tell your doctor why abnormal activity happens. For example, it can't find any problems in your brain caused by an injury or tumour.
During an EEG:
Sticky pads are placed around your head and these are connected to wires
The wires carry information to a computer about the electrical activity in your brain
The computer records the activity in your brain as a pattern of waves and spikes across the screen.
People with epilepsy often have abnormal brain waves, even when they are not having a seizure. 
The EEG itself doesn't produce electricity, and it isn't painful.
You may be asked to stay awake the night before the test. And if you're taking drug treatment for epilepsy, you may be asked to take a smaller dose before the test.
During the EEG, you may be asked to sleep or breathe deeply for several minutes, or a strobe light may be flashed in front of your eyes. These things can help trigger abnormal activity in your brain so doctors can see it during the test. 
An EEG can't say for certain that you or your child has epilepsy.
If your EEG is abnormal, you still may not have epilepsy.
And even if the EEG is normal, you still could have the condition. Sometimes abnormal brain waves happen deep inside the brain and they don't show up on the EEG.
Only about half the people who keep having seizures have an abnormal EEG.   
If a first EEG doesn't show any problems, you may have another. The second test may last longer than the first, and a video may record how you act during a seizure (if you have one during the test). This can help doctors find the part of the brain where the seizure happens. Brain pictures