I would say personally it all depends on the test, though that is just a guess as I have only taken one. I assume one could make a fairly accurate IQ test, but even then you would only be testing for certain elements of intelligence.
For example of the WAIS test that I took, I do not think it was a fair measure of a persons reasoning skills at all. Some of the methods used where in comparing words and asking how they were similar. I have a problem with this not because of what is being tested, but how it was tested at least for myself. It was clear the instructor was looking for one specific relation between the two words, and they didn't give a clear meaning of what they were looking for. They never said if they wanted an abstract or a direct comparison. So when asked I just threw answers out there, and what I saw was the instructor waiting til I gave one specific example. Which I think is bullshit. If a person can give you hundreds of comparisons, and someone else can only think of one; Yet the one they think of is the comparison you are looking for then the person who could only think of one would get a higher score. Which I think is just plan silly. This was how it was for any word analysis on the test. While the instructor didn't pick up on it, I was watching her very carefully. I was monitoring her actions to be sure how she was testing me.
There was also the issue with each category that was tested for being only tested for individually. We know the Corpus Collasum is responsible for the interaction between the two hemisphers of the brain. A person can have strengths in this area, so shouldn't we also do tests which rely on multiple categories to get an indication of how they put everything together?
Another complain was how knowledge was integrated into the test. While I do know Crystalline intelligence is based on knowledge I do think it is based on wither you know a particular word. I think it is based on the amount of knowledge you have stored in your head to refer back to. So when you just test for a persons understanding of certain words you are being bias. A kid who has studied physics and math, biology, and various other aspects. Yet did not study literature might have a lot more information to refer back to, than one who just studied literature. The test however would give different results. Which again I just think is silly. In honest regarding testing of knowledge, I think you should test for as many words as possible. You should test for a persons understanding of the word, not just their ability to give you one definition. Can they describe how it functions, can they describe certain aspects of it? This wasn't tested for. I also think if something isn't know it should be stricken from the test, and the category should be measure the same way, as if the person had answered all questions. We would then have to have difference confidence levels for each person taking the test, but I think it would be more accurate. Though I need to do more research to be sure, as others have said intelligence is not simple at all.
I am going to stop now, I could right a full length article on the problems with test. Which considering my grammar and sentence structure is poor would be a bad idea. The point is I did not think the test accurate. And I must acknowledge that I can't know for certain if I would have done better or worse had it been more accurate, as all those aspects that impair it's accuracy would effect other test takers as well. I think where these tests shine is pointing out if someone is mentally handicapped or not. That would be something I feel the processing speed and working memory categories could to some degree measure accurately. Though focus can also impact those scores, so even then it wouldn't be perfect, but it would be alright I think.
At the end of the day it doesn't really matter too much anyways. I say aim for the stars, try and go as far as you can. If you don't make it well at least you tried. May an IQ test be accurate at measuring intelligence? Some of them likely are, but even so what matters is can you do what you want to do. If you want to be a physicist or a philosopher will an IQ test tell you that you are cut out for it? I don't think so, what will is actually trying to go into a field and seeing how well you perform.