We have a set of extensions which have their tests run in CI for MediaWiki core changes. I would argue that EventBus extension has become critical enough in our infrastructure to be added to that list, since it's now responsible for:
- Submitting all jobs in WMF infrastructure
- Submitting all purges
- All main events go through the extension
- Some analytics events
The test suite for the extension is fairly compact, so it shouldn't add too much overhead.