Do food intolerance tests work?

I have had three different types of food intolerance tests done over the years, inc one the last couple of weeks, and I still don't know for sure. The first one I had done in Holland and Barrett's years ago and was an electrode test. Don't know how reliable that one was. Several years ago I had the pin prick test done twice, and I think that was a bit more reliable as it did come up with the fact I am intolerant to dairy. Recently I had a hair analysis test done. I'm even more unsure about that one. It came up with I am intolerant to wheat, which my body had told me was the case, but it also came up with that I am intolerant to yeast and things with yeast in like Marmite. This I'm not sure about even though I had been eating a bit of Marmite recently and all my gluten-free bread foods have yeast in, too. Also, it didn't come up with dairy, but ice cream and not butter, and I know for sure butter makes me ill. I know that I am intolerant to gluten, as foods with it in gives me stomach pains. So, what do I believe? Don't know anymore. What do you think? Have you had a food intolerance test that has made you wonder about it? Let me know.