Earlier quoted context omitted.
This always gets repeated, sounds good and makes sense theoretically but in reality there's no good way to do that and it should be the job of a computer to that. Restoring one file from the backup, works but what if something else is corrupted? Restoring the system from the image, works but what if some directory is not in the backup and you don't see that while testing?
I think the point is that if your data is valuable enough for you, you can't really trust that option in the backup tool to work - maybe you misunderstood some config option and the test now isn't really run, the tool is broken, or is run only on some of the backup files or dirs etc... or your original config might have missed a folder because it was mounted through some other filesystem (happened to me with Borg act…
Reling on software with good defaults that a lot of people use is probably a relatively safe bet combined with a second or third backup system (Personally I use Backblaze and Time Machine).