I recently asked the same question because my 4 year old son had to have the scratch tests done recently.
I know it is common for the testing to be done on the back, and I've been told that when they do it on the back, they do rows of allergens at a time, but they did my son's on the inside of his forearms. The took individual little plastic things, maybe the size of a plastic thumb tack, but with no visible point or anything on them but must have had some kind of sharp tip containing the allergen on it, and individually "scratched" each allergen onto his forearm. Each scratch was very quick, and to administer like 28 or so scratches, it might have taken one minute, total? It was very quick, and not painful. My son first started laughing when they started, I think it almost tickled? As they got more done, his laugh turned more into a half laugh, half wimper, like he didn't know if he should laugh or cry? But it was so quick, that he didn't have time to really get upset. And I can assure you that if it hurt, he wouldn't have been laughing at all. The harder part was waiting for the results to develop. My son has a peanut allergy, so that particular allergen caused a huge, itchy welt to develop that was really bothersome for my son. Of course he wanted to scratch it, and it was irritated. And the other welts that developed for his other allergies itched, and you can't scratch until the results are observed by the doctor. That was the hardest part, and even that wasn't bad at all. I just kept blowing on his arms, and he was ok. And we only had to wait like 10 minutes, after which time, the itch had worn off mostly, and they wiped him with alcohol wipes, which I think further killed any remaining itching. I've heard that often after the testing, if there is remaining itching, they'll administer Benedryl, or spray Benedryl spray on the welts to help with itching. My son had a lot of reactions/welts, and he didn't even need this. And again, he was only 4, so as an adult, this should be no problem at all.
Having seen my son do it, I would have no problem subjecting myself to the same testing. Best of luck to you.