Enter service mode -> tests -> single switch test -> toggle left with "volume +" button until you see 10 LEFT ORBIT on screen.
Take one ball manually out of the trough, and move the ball between A and B
If inductive switch is working you should see it change to ACTIVE(L) and you will also hear the change if you have sound on.
While moving the ball between A and B switch will change between INACTIVE(H) and ACTIVE(L) - Then test is passed!