what is this?
I can find no evidence that this exists.
There is no precise test for autism.
> A comprehensive evaluation requires a multidisciplinary team, including a psychologist, neurologist, psychiatrist, speech therapist, and other professionals who diagnose and treat children with ASD. The team members will conduct a thorough neurological assessment and in-depth cognitive and language testing.
National Institutes of Health (https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Educat...)
> ...a formal developmental evaluation may be needed...done by a trained specialist, such as a developmental pediatrician, child psychologist, speech-language pathologist, occupational therapist, or other specialist. The specialist may observe the child, give the child a structured test, ask the parents or caregivers questions, or ask them to fill out questionnaires. The results of this formal evaluation determines whether a child needs special treatments or early intervention services or both.
Centers for Disease Control and Prevention (https://www.cdc.gov/ncbddd/autism/screening.html)
I think what most people mean when they say it's not worth getting diagnosed as an adult is the second type, because the only thing it really does is force schools to provide adequate care for students.
I recommend seeking the first type though; I was diagnosed at 30 and it was worth it just to know. I only slightly suspected it though, and the diagnosis is what put me on the path to finding the communities, research, etc., which is ultimately what I got out of it -- so YMMV.
EDIT: Oh and meds! There aren't autism meds, but autism is often linked with anxiety or ADHD, and those can be helped with meds. Diagnosis is a first step to that.