There are several tests online, but none of them has a diagnostic value. They can give a first idea and encourage them to turn to a professional, but none confirm or deny being in the Autistic Specter. Some of the tests found online can be the same as those administered by professionals, but within a diagnostic process this is done in an assisted manner and serves to create a profile of the person.
You can find one wide choice of tests (including the RAADS-R used by some professionals in the diagnosis phase) on Neuroscapes, site created by David Vagni or you can do the Aspie Quiz that you can find here: www.rdos.net/it
To have a diagnosis of Autism Spectrum / Asperger's Syndrome it is necessary to go to a experienced professional in this field. It can be a psychiatrist, a neuropsychiatrist or a psychotherapist. Through various interviews and the administration of various specific tests he will be able to make a diagnosis.
Autism NOT a disease, But a neurological condition, a different way of being. We are born and die autistic, we do not "get sick of autism", nor do we recover.
Terms like "ILLNESS" and phrases like "AFFECTED BY AUTISM", "SUFFERING FROM AUTISM", are totally incorrect and do not represent autistic people.
They exist only paths to improve the quality of life of autistic people.