Q: Does Apple HW Diagnostics, include hard drive tests?

I'm having to reload my HDD. I have most data backed up and ready to go but want to make sure the HW is good first. I ran extended HW tests and it reported all "OK". I originally had a "grey screen" issue at "start up" with spinning gear, but that has not happen since I ran "verify" and then "repair" after I had some reported problems. SMART continues to say "verified" which I believe it's good(at least I believe that).

Does anyone know if the Apple HW tests include HDD diagnostics? It wasn't very clear it did. Or is it separate diagnostics?

Thank you in advance…..jerry