One owners food allergy testing experience:
WARNING: This testing should only be performed by a veterinarian experienced with dermatology or a specific canine dermatologist who can perform it properly  evaluate results then provide input form possible treatment.
“As some of you know we were having a lot of problems with one of our pups, Happy Girl, and her allergies. She had constant hot spots, scratching, and was often on antibiotics, etc. I knew at least some of it was food related, and we tried various foods. It would work for a few days then her symptoms would kick in again. Our vet consulted with a dermatologist, but the poor dog wasn’t getting much relief, and while our vet was more than willing to refer us to a dermatologist, she said in her experience it didn’t always work. I was planning on trying Dr. Dodd’s saliva test first, before trying allergy tests through the dermatologist, but even her test is $150-250. I’m a member of a dog allergy group online and someone suggested Glacier Peaks Holistic. I wasn’t 100% convinced, but for $85 I figured it was worth a try. It tests sensitivities for both food and some environmental things. Happy’s test came back with a lot of food issues, not too much environmental, and of course everything I tried had sweet potato or potato in it – and she had sensitivities to those things. Some of the things they test for we would never give a dog, but apparently this test can be used for people as well, though Glacier Peaks concentrates on animals. I considered switching her to raw (and I’m still considering – thank you for all the suggestions!) but wanted something I could try her on immediately. As the goal was finding a food with none of her triggers it was hard, but we found California Naturals Venison and Lentils. No more itching!!!! Finally hot spots are healing up, and she is feeling so much better. She does have some sensitivities to grasses, and we currently have her on the generic equivalent of chlortrimeton as well. As Jake has minor allergies, we have decided to go ahead and test him to make sure we don’t give him all the wrong foods like we did Happy Girl. The company does want to sell some of their products of course, but I found the allergy test very helpful. Just wanted to throw this out there as the allergies and itching can be so frustrating.”

One owners physical environment allergy testing experience:
WARNING:This testing should only be performed by a veterinarian experienced with dermatology or a specific canine dermatologist who can perform it properly evaluate results then provide input form possible treatment.
“Two of our non ME dogs suffered for 2 years with severe itching, rashes, and scratching. Our veterinarian had tried changing foods several times, then sent us to a canine dermatologist for evaluation. She ran skin tests on each dog then had results evaluated off site. They came back with 1 one of them having reactions to 13 allergens…mostly airborne and the other with 15 allergens. She explained thoroughly that these were not issues we could change to their environment as all were outdoors. She prescribed vaccines for each dog specific to their issues, but also started them on a program of medications to get rid of the affects they were suffering prior to starting vaccines. It is now 4 years later and though they periodically have minor flare ups, they are happy, have no more issues with excessive itching and scratching and can safely be outdoors around the allergens that showed on their screenings. This takes diligence with follow-ups to make sure they are still “clean”, but the pay off is so great with happy, healthy dogs.”

Here are two more options that could be reviewed then discussed with your veterinarian:
https://spectrum.vet/
https://www.nutriscan.org/