test: split envtest/real cluster tests

[fabriziosestito]

Description

This PR splits the controller tests by using the fast and slow testing pattern.
It is now possible to run only certain tests against a real cluster while leveraging the envtest fake
Tests that need a real cluster to run must now be labeled with real-cluster.
See https://onsi.github.io/ginkgo/#spec-labels.

kubernetes API server as the default test environment.
The policy server controller test was refactored to run envtest, which means that some assertions (for instance the ones on the Pod being created) are not possible anymore. However, they are not needed as we are not interested in testing that Kubernetes works.

Also, this PR:

• updates the Makefile to v4, customizing the targets as needed fixing: Update the Makefile after kubebuilder v3 to v4 update #786
• adds integration-tests-envtest and integration-tests-real-cluster targets to the Makefile, and updates the CI accordingly.
• switches to the ginkgo test runner, adding a flag to enable GitHub action format output
• enables parallelism for the real cluster tests. There is still work to be done for the PolicyServer controller test, which is tracked here: Parallel PolicyServer controller test execution and clean-up #792
• adds testing developer documentation to CONTRIBUTING.md

Note: the test coverage seems to be dropping by 1/2%, by looking at the codecov report this is because the refactored tests are not causing errors due to conflicts so we are not passing through the error handling lines.

With these changes, the CI is taking ~6 minutes instead of ~28 minutes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.79%. Comparing base (807090f) to head (4e341e1).

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #788       +/-   ##
===========================================
+ Coverage   31.90%   69.79%   +37.89%     
===========================================
  Files          13       23       +10     
  Lines         536     1705     +1169     
===========================================
+ Hits          171     1190     +1019     
- Misses        361      396       +35     
- Partials        4      119      +115     

Flag	Coverage Δ
integration-tests	61.64% <ø> (?)
unit-tests	31.90% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[flavio]

AMAZING work 👏

I left some really minor comments, this is good to be merged

[flavio]

TODO: cache this step, maybe file an issue for that

[fabriziosestito]

I am experimenting with something atm. Kubebuilder generates a Makefile that installs the needed tools in a bin directory in the project root. We could add ginkgo to the automatically installed tools, cache the bin directory, and invalidate the cache if the Makefile changes. WDYT?

[viccuad]

That sounds fine to me, provided the tools versions are pinned in the Makefile. We have that layout in other repos.
I would prefer a GH action because they can or tend to verify the tools prior to install, even if that means that we manually sync tool version in makefile and GHA.

[viccuad]

LGTM! ❤️ , plus the CONTRIBUTING.md docs.