Autism is diagnosed through a series of cognitive and behavioural exams. There is no genetic test for it.

Links between genetics and various ASDs are still only being understood and it appears to be more complex than simple genetics. In utero conditions and environmental factors may play a part.

So even if/when there's a genetic test it would be merely a probability indicator rather than a dead certainty.

If you believe you may be autistic, you must talk to a proper psychologist. There's no shortcut/free test.