The application was primarily designed to be viewed around 1080p. We've built in some quick and dirty (honestly, hacks) to display a usable layout at other resolutions. A more thorough redesign / refactor is in order, again if there's sufficient interest. What's available now should handle a lot of situations ok. If you find performance / layout is not looking great at your given resolution, try to use a desktop browser at a 1080p resolution.
As of our initial release, the test suite only tests the backend (and coverage is admittedly not as robust as we'd like). We'd like to add tests for the frontend, though this is a fairly large undertaking. We welcome any contributions on this front!