Generation of checksums.h in tests

[Artem Leshchev]

Hello.
I'm trying to get grub_func_test PASS and have found, that it depends
on some pregenerated checksums (saved in grub-core/tests/checksums.h),
which itself depends on unifont. In my environment something differs
and checksums doesn't match.

I've found in git log that this file sometimes regenerated for new
versions of GRUB and unifont. I wonder if there is some script to do
this. Looks like there is should be established process for generating
this stuff.

Other interesting question is "golden screenshots" checksums based on.
Are they published somewhere? Can they be generated from checksums.h?

Looking forward for answers.