From what I've read (and been told by my allergy doc), food allergy testing is just simply not that reliable. I was tested for about
50 food allergies using the standard scratch tests on my back, and I came up positive for a few things. So I removed them from my diet but didn't notice a thing. When I re-introduced them back into my diet I didn't have any reaction either.
My allergy doc said that food allergy scratch testing isn't very accurate. It's pretty good at predicting negative reactions (ie, if the scratch test comes back negative, there's a good chance you aren't allergic). But it can have a lot of false positive reactions (the scratch test for a particular food is positive but you can eat that food with no reaction).
There are other types of food allergy testing, including blood tests and stool tests looking for certain antibodies, but those aren't backed by solid science. So I'd say they're even less reliable than the scratch tests, which aren't that great to begin with.
You might be talking about food sensitivities, which are even more difficult to diagnose. There are labs that will do blood or stool tests for these, but most medical doctors don't put much stock in the results. There may be some value for you to do this - so I'm not saying it's total bunk - but just know that the mainstream medical community is skeptical of these types of tests.