During our brainstorming of T279322: Design m8s deployment workflows and tooling, it became clear that the correct way to run tests against code that is also being packaged into an image is to include those tests in the same pipeline build process. We should see how feasible it is to port the tests and CI jobs that test MediaWiki during gate-and-submit to the mediawiki/core .pipeline/config.yaml and blubber variants.