Here's an interesting one for you. I used to build test boxes to test reclaimed flips off of DBR (damaged beyond repair) cell phones. Box I'm going to show you is for a Moto 402/502 flip.
Basic operator instruction where..
Flip all toggles up.
Turn main power on and press Start.
After all Flips go into test mode...flip down toggles.
Press soft button to advance threw program.
Program tests inside LCD, outside LCD, camera and flash (if available), and any buttons (if available.) This test program is standard on all Moto flip models on Sprint phones.
I built these boxes off hand. No diagrams to work from. Figured power out on each new model. Other brands required to test the entire flip w/o a program all functions had to be accessed manually. Anyway..that's just a sample of what I built.