It depends on what kind of allergy testing you want done and whether or not your insurance will allow you to make direct appointments with specialists. Serum allergy tests can be ordered by a PCP using a blood draw. Epidermal "prick panel" allergy testing would need to be done by an allergist. There is also something called ALCAT food sensitivity testing. We use the term "allergy" rather loosely and differently than it is used in medical settings.  All food allergy/sensitivity testing is problematic and the results often do not agree with each other or with actual symptoms. It's worth doing some research as to reliability before you dive into it.

How do you do allergy tests? The primary doctor sends you to an allergist?

1/1/2 slices of bread is likely not enough. Current guidelines for the gluten challenge are recommending 10g of gluten daily which is about the amount found in 4-6 slices of wheat bread. Physicians in practice are often working from outdated info.

Please list the ingredients of the granola. It may have nothing to do with gluten but an allergy or sensitivity to some ingredient.

I have alerted surgeons that they need to check with manufacturers and labs to vet the anesthesia. My hands surgeon did that and I was ok so reconstruction surgeon called her to use same anesthesia. They certainly wouldn't have taken just my word.