Greetings and welcome. In my experience the online tests are actually a fairly good gauge, although of course they are hardly perfect and the questions can be a little vague at times. When I first suspected I had AS, I took several of them, and they proved quite accurate. The most complete, IMHO, seems to be http://www.rdos.net/eng/Aspie-quiz.php, but if you prowl this forum you'll find several others.
If nothing else, by reading the posts here and asking questions in a supportive environment such as this, you will learn a great deal about AS and once you see a professional you'll be able to discuss the subject far more intelliigently. In my case, this proved to be extremely important to a good diagnosis.
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Scientia est Potentia