I have crohns. Would I benefit from a food allergy test to try to control my symptoms. ..Mainly diarrhea?

Yes. It would definitely not hurt your cause. Food allergies and sensitivities can commonly cause repeated bouts of heartburn, irritable bowel, and general GI distress.
Maybe/not. Any allergy testing has its limitations. Both skin or blood testing can miss or over diagnose food allergies. They would also miss food sensitivities that are not based on allergies. They can be a guide on things to avoid, but sometimes a food diary & keeping track of what seems to aggravate symptoms will do more good.