I see an allergist on a regular basis. I've had all sorts of allergy testing done. I can honestly say I've never heard of them being able to test for allergies to meds. I am allergic to sulfa-- I found out by taking it (which I had taken it many times before that).
I've had skin testing done multiple times-- but like I said I didn't know they could test for this. An allergist is usually used to pinpoint and define a treatment plan to help allergy sufferers. There really wouldn't be a treatment plan for this, other than to not take it.
Just out of curiosity they did say they'd do testing for allergies to anitbiotics?