I get an error when running diagnostic tool on macbook with intel processor. The macbook is up to date with macOS Catalina 10.15.7.

It is not surprising your older Mac (likely 2012 or 20113 or thereabouts, right?) is not able to use Apple Diagnostics.

Apple Hardware test is the correct solution for Macs introduced before June 2013, and (as you discovered) Apple Diagnostics does not work for older Macs.

How to use Apple Hardware Test on your Mac - Apple Support

This requires you to have NEVER erased or replaced the boot drive where the diagnostic was initially placed, but no software was responsible for keeping it up-to-date to re-placing it if lost.

If you have the original release DVD, it is on disc 2 of 2.

what is your complaint? what is driving you to run diagnostics?

Hello cyborgmistress,

Welcome to the Apple Support Communities. From your post, Apple Diagnostics is having issues running on your MacBook. We'll do what we can to help.

If you've tried the key combinations at startup a few times, try reinstalling the tools by reinstalling macOS: How to reinstall macOS

If you still have issues, reach out to Apple directly: Get Support

Take care.

Grant Bennet-Alder wrote:

It is not surprising your older Mac (likely 2012 or 20113 or thereabouts, right?) is not able to use Apple Diagnostics.

Apple Hardware test is the correct solution for Macs introduced before June 2013, and (as you discovered) Apple Diagnostics does not work for older Macs.

That is not necessarily correct. Beginning with a patch to macOS 10.12.x (maybe .4 definitely by .6) Apple updated the system firmware for the 2010+ laptops to allow them access to Internet Recovery Mode and to the online Apple Diagnostics (the online diagnostics leverages the Internet Recovery Mode framework). Unfortunately with another system firmware update Apple broke the ability to boot to the online diagnostics for some systems which ends up with the error regarding the "TestSupport.efi". The updated system firmware also breaks the older diagnostics as well with a similar type of error.

All of our organizations Macs have had the drives completely erased so the original diagnostics stored on the drives are long gone, but all of our 2010+ Macs have access to the online Apple Diagnostics when they are not broken by some compatibility issue.