I have IBS. I stopped eating dairy products and it has helped a lot. I try to avoid all high acid and high fat foods as they cause problems. That means, in addition to dairy products, cut back on tomatoes, coffee, chocolate, high fiber foods (e.g., oatmeal) and anything deep fried.

There really is no test for IBS. For a diagnosis, you have to eliminate certain foods from your diet and see if that makes a difference.