My grandson had a hearing test around 8 or 9 months. He didn't even respond to a drum being hit behind his head. I know they know what they're doing and I wish I could tell you more but they can tell if he hears some sounds. It won't be as detailed as it would be if he could hear them but they'll be able to find out what ranges he can hear and what he can't.
It was the best thing that happened to my grandson. They doc suggested they do tubes in his ears just to see if it would help. Then a few months later he suggested they go back in to put in a cochlear implant.
When the doc went in he found all sorts of debris left over from old ear infections that antibiotics had not touched. That baby had been on Zithromax several times for ear infections and I know he got his meds.
The doc cleaned out the ear canals and put the tubes in. When my little grandson woke up he could hear again. It totally freaked him out of course but he could hear. No more surgeries, no implant!
I hope if the docs find anything wrong in the hearing test it's fixable and that he will be able to hear.