Brother Durham explains the diagnostic test kit available for GE refrigerators:

If you do a lot of GE fridge repairs, you may benefit by getting a diagnostic aid shown in the following video. It is, in essence, nothing but a control panel that you can use and will bypass the one in your fridge, whether it is a similar panel, knobs or lcd screen control found at the dispenser. With such a panel, if you connect it and everything works, then you will be certain you have a bad control panel.

btw, the part numbers needed for the aid have been changed. Instead of the three parts mentioned in the video, you need two WR55X10390 (interface and touch panel kit) and WX05X14999 ( wire harness). I got one a few weeks ago and it paid for itself in a few days.

ps you can make one of these by removing a 5 key control interface from an otherwise dead GE and then purchase the harness.

To learn more about your refrigerator or to buy parts, click here.

Source: GE Ref PDS22SCRBRSS No control board operation