If a child has had no allergic reaction (yet), should we test her for allergies anyway, just in case? Or, is it enough to react after an allergic reaction?
If there has been no allergic reaction then there is no need to test with two exceptions.
Family history of a lethal reaction. For example if Grandma is allergic to fish, and Mom is allergic to fish, then be extra careful with fish around the child.
Doctors advise allergen testing. I'm not one to say blindly follow doctors' advice, but if a doctor is telling you to get the testing done, then get it done.
With most allergies, common signs will show LONG before a lethal reaction occurs. For example, hives, rashes, watery eyes and running nose will all be very evident with non-food allergies long before any serious complications arise (normally). Food allergies often present as a sore throat or upset stomach, long before the "I can't breath" point (normally).
Even if you do get allergen testing, they don't test for everything, just common things, or things they think have triggered the reaction. The testing can be very unpleasant if the list is long.
Best advise is ask your primary care physician.
If there are no allergic symptoms you don't actually need to test it proactively. Yes if your child has running nose or constant cough or some ongoing allergic symptoms. it is time to find out what is the reason & how it can be handled. Know complete details about childhood allergies & treatment plan here. http://www.ssdhospital.com/childhood-allergies/