The only type of test I've had for this is a blood test, and my consultant rang me to say that my magnesium is low, and I needed to start on Magnesium Glycerophosphate as soon as possible.
I started to take them yesterday, and have noticed that my bone and muscle pain is a little better today than usual. Which is a good start.
What type of magnesium test did you get, have the copy? Please look this up.
Supposedly magnesium citrate (as opposed to mag oxide) is absorbed the best....its a little more costly too.