The mediawiki/tools/api-testing repo contains integration tests for the MediaWiki action API. It should have a CI job set up that ensures that all the tests in it pass against the current master version of MediaWiki.
The job needs to do the following:
* spin up an empty MediaWiki instance
* run `npm install` to pull in any dependencies (from a local mirror?)
* adjust config.json for the target wiki
* run `npm test` to run all tests
A similar CI job could later be added to the core repo, to ensure that any patches submitted for MediaWiki core don't break the API.