Skin tests just show immediate onset, IgE mediated allergic responses.

Any food allergy/sensitivity that is delayed onset and is not IgE will not show up. But biopsies are not the only option. (I know only of biopsies for celiac, not for any other food intolerance.) There is blood testing, something offered by kinesiologists, and probably more. (I don't know much about these alternative tests, just that folks have used them). I went with fecal testing with Enterolabs which looks for antibodies for gluten, casein, egg, soy, and yeast.

I had skin testing years ago which found nothing. My Enterolab results are positive for everything. I've eliminated these items from my diet with success.