I haven’t looked through the Jerboa codebase very closely yet (I downloaded it, but that’s about as far as I have got so far), but it sounds like they either need more code coverage for their unit tests or they need to improve the quality of the unit tests. Good unit tests should catch a lot of bugs introduced by PRs. There is no QA team to do regression testing for each release, and the main developers can’t be expected to run manual testing for every PR. The developer of the PR should be doing that, but clearly they are not.