Some internet tests aren't meant to diagnose anything more serious than how addicted you are to World of Warcraft. Others may help you determine whether to bring a nagging health concern to your doctor, or give you a rough idea of whether a health problem you're already aware of is becoming more severe.
Internet tests and quizzes can't substitute, of course, for in-person evaluation by a health professional who can discuss your concerns holistically and check for other problems that a narrowly focused quiz can't cover. But if used properly, a well-written test can be a great tool. Here are some that folks who have or suspect food allergies might find useful: