It can be checked with an ohm meter while it's disconnected. If you have continuity, the leads going to it can be tested for voltage. After that, it comes down to pressure switches, etc. Also if it's the ignitor, the gas valve should click and possibly get a brief whiff of gas.

Super. Appreciate the info. Do you know what voltage goes out to that lead? Don't want my service man to blow his multimeter.

So if I have a brand new ignitor not installed in the furnace yet and the tech were to run the ohm meter to opposite sides of the lead for the ignitor, it should measure some amount on the ohm meter, correct? And conversely, a bad ignitor would register nothing across the leads?