You'll basically be tested on things such as your abilities reactions under certain situations, like those that create strong emotions or stress and also there is a dueling test. During these your ability will be monitored for the strength and then they'll be able to create a limiter specifically for you.

They also like to re-test once a year at the least, just to make sure there aren't any changes to how strong the psychic ability is and if there is, they can make adjustments to the limiter as needed.