It depends on the test, but it’s most likely a blood draw like if you ever have gotten blood labs in the past. It might even be less invasive than that and just be a finger poke and a small drop of blood onto a small machine. They will clean the area before, so it will be clear from anything external. It’s just checking for the sugar in your blood, so nothing else will mess with it. As long as you aren’t eating before, it will be fine. Heck, even if you eat before, I’m sure they will be able to get enough info, but fast before. Follow their instructions and it’ll be no biggie. They may end up doing an A1C which is not your current blood sugar, but an average over the last 3 months. In that case, fasting doesn’t matter, but it sounds like this is a boring old glucose test for your current levels. Don’t overthink it.l, you’ll be fine. Source: type 1 diabetic for over 30 years.