The ones DS has had (and my opinion on them) are:
RAST- Blood test, the results come in readable units and are interpreted into several degrees of seriousness. The fact that you have a very high result doesn't necessarily mean that the reaction would be more severe, it only means that your likelyhood to react to the allergen is very high. ie. this test just managed to catch DS's allergy to milk barely but if he has milk you can see the reaction building up immediatly. His readings for egg were 100 times the limit but he has had it cooked before the tests and he was relatively fine.
Skin Prick Tests- As the name suggests they do a prick on the skin after applying a drop of the allergen serum to the area. They allow a few minutes for the reaction to build up before the doctor measures the "bump" with a ruler to check how bad it is. What I don't like about this test is that it has some scope for human error, ie. DS reaction to peanut was immediate, faster than to the histamine they put to check the test works, but the clinic was running a few minutes behind and they measured the spot a few minutes after the recommended time, by then most spots were subsiding and it could have been appeared as if the allergies were less severe than at the previous test one year before, however... they were not less severe, they were late in reading it.
ELISA. Nice thing about this test is that you can test a lot of allergens with just one blood sample. If you have no idea what may be causing a reaction this may be a good place to start as you would be able to shortlist some possible culprits before asking for a more reliable test. However, this test is very UNRELIABLE hence the importance to double check with a second different test. It is availble commercially so you don't need to wait for months to hear form the allergy clinic.
Homeopath tests. Well, yes, he has had them, not because I trusted this testing (it was the last test he had) but because I wanted to use homeopathy to treat some of his allergies once the doctors has said there was nothing else that could be done for him. Curious thing about this test was that the homeopath tests showed positive for the same allergens the other tests had confirmed, but and HUGE DISCLAIMER here:
it has took me ages to find a homeopath as good as the one he is seeing now, I have seen some changes and eventhough I'm very sceptic of this things I have started using it myself with good results, however, I have also seen a few other homeopaths with NO results at all, or even worse, some who advised things that clearly showed they had not a clue of how dangerous their advice was.