I use a multi-meter and do continuity tests on them.
Using the FSM schematic wiring as a guide,I "turn on" the switch and check each connection pertaining to the setting the switch is at.
Pretty simple actually,Red terminal on my meter I use as power going in and black as power going out.
The spades on the switches are marked as well.
My multi-meter has a setting where it beeps when I close a circuit.
Hope this helps.