Dear Joanna,
There really is no test, per se, for ADHD. Rather, it is a descriptive diagnosis based on the presence of a particular array of eighteen symptoms. If a sufficient number of symptoms are present, before a definitive diagnosis of ADHD can be concluded, it's necessary to determine if there is any other reasonable explanation for the symptoms other than ADHD. In other words, other conditions need to be rules out.
Some non-verbal learning disabilites can look very much like ADHD, particularly if the disability impairs a person's ability to be organized. In addition, some
sensoryNumbness and tingling integration problems can sometimes be misdiagnosed as ADHD.
One thing to keep in mind is whether the symptoms tend to impair the child's ability to master the important areas in his life. Many children display symptoms which might warrant the diagnosis of ADHD, but the symptoms don't really interfere with their functioning. Impairment is necessary to meet the criteria for a diagnosis of ADHD.
Have you ever heard of the Thomas Edison syndrome? There are many books written about this subject. Do a search and you'll find many books on this subject. Good luck!