You can skip the electrical checks for the most part. You can verify continuity or lack of it through the heater and thermostat but a visual check is usually enough. If you see ice on rear panel it is not defrosting itself. One of 2 things has probably happened:
1) Defrost heater has failed. It's in a glass tube and tends to leak until the wire element corrodes away. This is most likely.
2) Defrost thermostat has failed and won't power the element. It will open at 30 deg I think so by the time you've defrosted it it is often going to be open and look bad anyway.

Unplug the machine, take the rear panel off and manually defrost the bottom of the evaporator to expose the element. You can use a hair dryer, heat gun, steamer, time, whatever. Use nothing sharp and no forceful actions however.
Odds are good you'll see a broken glass tube with a nice shade of green inside. That's your element. Look for burnt up connectors at the element ends as that sometimes mimics a bad element.

Older parts came with both thermostat and element so you didn't care which it was. Odds are it is the element down at the bottom and not the thermostat but you can change both if you truly want to cover your bases.

#230 is the element and 240 is the thermostat on this diagram. Measure the element to make sure you need 9" or 12" model.

You'll want to defrost it as much as possible before restarting it. Prepare for water to overflow from the pan in back bottom.

There's a very slight chance your main board in the back isn't asking it to defrost but I'd doubt that.

It's not bad it just takes some time. I fully defrost the evaporator so the machine begins cooling immediately. If it's already empty and you're not in a rush you can just defrost the lower section to replace the element and then wait for it to go into defrost on its own. In most cases it will defrost itself within 24 hours.

I forgot to mention that some of the side-by-side GE machines actually have two separate elements.#2 would be about midway up that evaporator. The replacement part will make it obvious if that is the case.
Definitely unplug the machine so it's not fighting back by trying to cool and so that the light isn't on and hot enough to burn your hand.

Good luck!

hi PNWDrew:
Here is sitrep on freezer defrost.
The coil was nearly a solid block of ice. After defrost removed heater and thermostat. Heater measured about 27 ohms, but close exam revealed a fracture and chunk of missing glass close to the connector. I could see the heating coil in plan view. I think replacement is in order as i'm only asking for trouble in the future, even patching it over with electrical tape.
The thermostat measures continuity even at room temp. I gather from your previous discussion it should be open at room temp. I still don't know how the thermostat works but i see replacement of it in order as well. Calling appliance part pros for parts today.
Ron