I am not trying to answer for
@BeginnerSleuther but lots of mental disorder diagnoses do not require "tests." It would be nice if there were presence/absence tests for disorders (score above X indicates presence of the disorder, score below X indicates absence of the disorder) but either there aren't any such tests or if there are, they are unreliable. I can't think of a disorder where there is a test for it that is accepted as THE test for diagnosis. There are, however, many disorders that require tests to rule out other causes. For example, poor academic performance might be due to the presence of a learning disorder. But problems with vision and/or hearing could cause poor academic performance too and must be ruled out. Poor academic performance could also be caused by the disorder of Intellectual Disability (formerly called Mental Retardation) While a standardized IQ test is used in the diagnosis of ID, it cannot be used for diagnosis by itself. Aspects of adaptive functioning must also be assessed, often through observation.
Per the CDC "Diagnosing autism spectrum disorder (ASD) can be difficult because there is no medical test, such as a blood test, to diagnose the disorder. Doctors look at the child's developmental history and behavior to make a diagnosis."
Screening and diagnosis of autism spectrum disorder.
www.cdc.gov
The DSM-5 criteria for autism spectrum disorder can be found here. (DSM-5-TR clarification to the diagnostic criteria included changing "manifested by the following” to “as manifested by all of the following.")
Read the full text for the diagnostic criteria of autism spectrum disorder (ASD) from the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).
www.autismspeaks.org
While a particular ASD evaluator might use a "screening test" and include mention of it in his/her report, the idea that BK should have been "tested" for autism as a child doesn't really make sense to me regardless of AT's motivation. In looking at the diagnostic criteria it's hard to imagine a test or even a series of tests given to a young child that could substitute for observation of his behavior in various situations.
MOO