here is what I do it. with the trailer hookup up set your trailer brake controller on the setting desired.

then drive the truck in a straight path with lots of room and apply the TBC only. Using this method you will want the trailer to be able to stop both the truck and trailer. not to the point of locking up the trailer tires but you want a real good stop.

This is me ensures that it works and if I need to stop real quick there is enough gain from the tbc to keep the trailer behind me.