Would some kind of device switching test case be feasible? In my experience that's where a lot of weird behavior creeps in. For example, plugging in a USB interface, using it, and unplugging it. Or switching back and forth between Bluetooth and wired hardware (or even changing Bluetooth headset mode back and forth between A2DP / HFP).

This is a great idea, I love it! Most of us now have at least two output devices - the usual jack output and a display connected over DP/HDMI. Not all monitors have integrated speakers, but some have a jack connector you can connect your headphones in. And that's exactly how I use it - speakers connected to my desktop's output jack, and headphones connected to my monitor, which allows me to switch between speakers and headphones in a pure software way, without replugging connectors all the time. Sometimes it causes some issues. This would be a great test case with Pipewire.

And as suggested by Brandon, other devices like USB headphones or Bluetooth headphones are probably even more common than my own use case. Let's cover this.