tests: add more tests

[lorenzofelletti]

In light of the recent issue with the API server availability rules, which was hard to catch by simply looking at the git diff, I think that adding more thorough testing is due to make repeating such a mistake harder in the future.

In this PR I'm adding more tests around the API server rules, and I'm also moving the tests to a dedicated folder, allowing to break the giant tests.yam file in multiple, more readable ones. The Makefile is updated accordingly, so to run all test files in the tests folder on make test.

[skl]

Thank you for doing this, @lorenzofelletti! I was thinking the same.

One thing to watch out for - there's a few dependabot PRs open which seem to depend on go.mod being bumped to 1.23, as well as the prometheus version being bumped from 0.53 to 0.300, for example:

• chore(deps): bump github.com/cloudflare/pint from 0.62.2 to 0.69.1 in /scripts #994

Note that the prometheus version bump appears to change the behaviour of the tests (understandable given how out of date the deps were).

I can fix these on #994 but you'll need to make sure to merge/rebase latest master branch, just wanted to give you a heads up in case your test behaviour is affected.

[lorenzofelletti]

Hi @skl, thanks for letting me know. I'll rebase/merge master to keep this in sync.