This commit adds logic to two unit tests where the schema
export is compared against expected output cached in two
schema files.
This is intended to help prevent bugs like the ones fixed in
116f6e4 or the immediately succeeding commit, as unexpected
changes to schema export will become apparent in the commit
diff, easing reviews.
When legitimately changing the export output behaviour,
the test suite just needs to be run twice, as the unit-tests
automatically overwrite the files with the new version.
This unit-test approach is inspired by
https://matklad.github.io/2022/03/26/self-modifying-code.html
