I'm pretty sure part of the assessment for an ASD anywhere includes IQ testing, but I'm not sure about the achievement testing at that time.

My son was diagnosed with an ASD when he was 3 and gets periodic IQ tests as part of IEP development for the school.

I cannot answer specifically about HRC, though. You are right to have your 6 year old assessed if you have questions, and the earlier the better!

Nan