Yesterday dove into one of the older animation jank bugs in niri: quickly resizing a window back and forth would cause adjacent windows to jump. This problem is hard to trigger unless you're specifically trying to (then it's easy), but it was causing "downstream" problems for more complex actions.
The fix was simple enough, but I imagined enough "interesting" cases around it and decided to write a whole bulk of tests. Check this out, all thanks to our layout and clock code!
