I think you can get a basic idea taking a test but things like feeling rushed or being worried you wont do good can change it. So could being stressed, not eating right, or being tired. Then there is always a bit of luck. It also depends on how often you practice. If you take a test twice a week you will score way better than someone who took their first IQ test, just because your more used to it.

I tried that test, I got 130. I don't have anything to compare it to so I can't say how close it really is. I notice something funny though. When it gave the results it said the average was Middle school graduates. I am not sure if that is true but if it was, thats pretty low for an average.