> git commit, which hooked into yarn test
There's the real wtf. How are you meant to commit a failing test? Or any other kind of work in progress?
You mark the failing test with "failing". The test runner knows that it might fail but doesn't fail the suite.
I'm not a big fan of git commit hooks, but it can give faster feedback than waiting for a CI runner to point out something that should have been obvious if you keep it light weight (such as style linting or compiler warnings).
Edit: replaced "Todo" with "failing" since we're talking about jest specifically: https://jestjs.io/docs/api#testfailingname-fn-timeout