How can I test if a dehydrator is getting to the proper temperature?
The manual for the Aroma 5-tray dehydrator says that the drying temperature is about 150°F (65°C). So all you need to do is find a thermometer that you can fit inside it, turn it on, wait 5-10 minutes for it to heat up, and check the temperature.

You could also simply test it by drying a quick test batch of something; if it gets nicely dehydrated in roughly the expected amount of time, the temperature was probably fine.