In my opinion it won't be such a good test as we (people with ADHD) also have what some call hyperfocus and moving things on a screen usually triggers it ... I was able to play GTA:San Andreas for 36 hours with no breaks (and no meds)... so a moving star will probably (not necessarily ) trigger hyperfocus so everything depends on the surroundings and the state of mind...
Just give him an very long Q&A test (with boring questions, and don't tell him what's the test about just to make it a little more boring and more objective) and observe he's behavior, slip a few questions in that test that are ADHD related like "Do you talk to yourself often?", "Crowded places disorient you?"(make sure you put them in the first 20 questions as he will start loosing interest in the first 100 questions and he won't probably finish it), and then give him something that he finds interesting,fascinating to read or do and then try to talk to him, if he's answers are "yeah", "mkay" and "mhm" and show you lack of interest and inattention in what you're saying... you have a potential (I repeat POTENTIAL) ADHD "victim"... (Fascinating things and movement on a screen = hyperfocus, Boring things = loss of interest and inattention to the subject of matter)
If you're kid is ADHD first thing you have to do is to educate him in what ADHD is, don't jump to medication (Adderall, Ritalin, Concerta etc.). Trust me he'll understand better than you think and he will not fall into depression when he's starting to grow up (I've found out that I have ADHD at 22 and between 15-21 I was going through hell not knowing what's wrong with me). Finding out that I have ADHD and what ADHD means brought peace and answered everything that was going wrong with me...
Hope it was helpful !
Good answer by loststylez.
I pretty well discovered the same thing when correcting kids math tests. If all of a sudden they were missing problems at the end of the test that they were getting right at the start of the test, then it was an indication to dig a bit farther.
I still need to check out the test you mention. It might work better on ADD than ADHD.