Disallowed Focussed Tests and how it saved my day

Today I was about to push a focussed test. A focussed test, you ask?

In Jest (and others) one can run only a specific test, by writing it.only(.... Pushing this to production might create some funny or not so funny side effects though. Luckily there is the no-focussed-tests linter rule in eslint-plugin-jest.