I don't know everything there is to know about testing, but I can tell you
from experience as well as research I've done, that skin testing is not
conclusive on children younger than a certain age (I'm not sure about the age,
but I think it's 7. Anybody?)
In any case, my son (then almost 2 years old) had 32 skin pricks done on his
back only to get no results at all. It turned out that in addition to an
anaphylactic allergy to cow's milk (for which he wasn't tested because we
already had clear evidence of it), he was allergic to many of the things they
tested -- dust, mold, cat and dog dander.
I had been keeping a history of his symptoms -- clear runny nose, ear
infections, asthma.
After the test turned up nothing, the allergist said, "Well, he's really too
young to get good results from this test. But your written history points to
several allergens. I think this is all we need."
Aaarrrgghh. After putting him through all that. I wished I'd known more before
I agreed to the testing.

I've done lots of research since then and got more info from the Food Allergy
Network. Then, last summer we requested the RAST (blood) test for my son,
particularly to see what the antibody count was for the milk allergy. After
the test, which was his first RAST, the allergist said he wished we had a
baseline to compare it to. I wanted to scream, since he never recommended this
test before.
Now, that test will serve as a baseline and we'll do it again this summer to
see if there's any improvement.

I don't know what other people have encountered in testing, but I felt the
RAST test was a better indicator -- and much less stressful for our son --
than the skin prick test. However, I understand that the only true indicator
of whether he's outgrown his allergy to milk is to give him milk or a milk
product. But as long as the RAST test indicates antibodies, we'll steer clear
of milk....it's far too risky.

Hope this helps.
Rose