testify makes most bog-standard test checks much easier to read and
maintain, and is quite widely used. It wasn't really well known back
when go-mtree was first written, but the migration is fairly
straight-forward for most tests.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>
During the rework of how xattr fields are handled, the comparison code
was not correctly updated. As a result, changes to xattrs would not be
detected in any form. This was detected in the umoci integration suite.
In addition, fix the dh.UsedKeywords logic so auto-detection works
correctly with prefix-based xattrs.
Fixes: ed464af779 ("*: xattr can Update()")
Signed-off-by: Aleksa Sarai <asarai@suse.de>