I've just noticed that the changeset for #5190 included some untested code. Specifically, there are no tests for the code which detects missing dependencies and emits warnings about them.
I'd previously noticed that this code was broken but hadn't realized this was because it was untested.
I don't think there's any disagreement whatsoever over Twisted's testing requirements. All code must have full line and branch coverage (as reported by the coverage.py tool). Developers, please write tests for all of your code (and please learn to do test-driven development - it will make this task easier, I promise). Reviewers, please don't accept proposed changes that include untested code.