Though allergists can do skin-prick tests that sometimes show evidence of food allergies, and some blood tests can indicate food sensitivities, these testing methods are not foolproof.
Furthermore, even with the possibility of a known food allergy, most people have no way of knowing what their symptoms are, or what the effects of the allergy or sensitivity might be. Sometimes the symptoms of a food sensitivity can be as mild as acne, where in other cases the repercussions can be severe.
Whether you've been diagnosed with a possible food allergy, or if you even suspect a food sensitivity, the best way to learn about how a certain food impacts your own body is a food elimination trial.