I had it with my last two pregnancies; with DD1 I ended up having the test 3 times, as they were convinced I had GD due to her size, and the fact I had polyhydramnios (I didn't have GD).
It's fine. Not being able to eat or drink anything, except plain water, can be a pain, especially if you feel a bit faint, but the test is (usually) first thing, so you can eat straight after.
You will be given a sweet drink (what we get given here is like very sweet lemon squash), and have to drink it within a certain amount of time. You will (here anyway) probably be told to sit still in the waiting room, for the two hours, this is because walking around will affect the results.
It's best to take some food to eat immediately after the test has concluded. As not eating, having something sweet, then not eating again, can make you feel ill, and here they like you to bring food to eat straight after.
If you feel ill during the test, tell them.
It's really not worth mucking around with something as potentially serious as GD. Don't put it off.