Hello,
I am looking for the AHT for MacBook Pro 15" mid 2012 (9,1)model currently running Catalina (10.15.7). I have tried multiple forums and even tried the GitHub steps, however, nothing seems to be working.
I would really appreciate if you can help me with the .dmg / image file for the same and the steps to follow.
Thank you ,
Sol
Thank you very much 
I got the much needed article at last.
I hope the below helps others as well.
@Cattus_Thraex: I downloaded the EFI dmg file. After mounting it, when I try to install. I get āThis version requires 10.9.5ā and I am unable to carry on the installation process, as it quits.
Can I burn it on an USB and then try to boot it from it? would that work? Please suggest.
Thank you.
YOu do not need to download anything, have you red the instructions in the suggested link? It seems you have not. If your mac is running Catalina, all you must do is to restart pressing the keys as indicated there.
I read through the article. In my case, when I press D, it takes me to internet-enabled connection via Ethernet or Wi-Fi, after passing that screen, I get an error code
Error: 0x8000000000000003, Cannot Load āEFI/Drivers/TestSupport.efiā
Status: 0x00000003
I cannot figure out why you get that error, unless you have a corrupt system installed. If you have a good, clean system (as you say) the operation should be smooth.
I had replaced HDD to SSD and had done a clean install, I think that might be the reason why I lost the hidden partition where AHT is installed.
I even tired the steps mentioned in the link below;
It starts the process and comes back to my login screen.
Upgrading to an SSD should not influence AHT as long as the system is up and running, supposing you installed it accordingly.