There are edge cases where the frame cache isn't updated but new frames are added to the UI. As an example, after someone makes visible their previously hidden raid/party frames but before they join a group for GROUP_ROSTER_UPDATE to fire. This matters for testing, mostly.

Is it reasonable to implement something like

function lib.ForceScan(delay)
    ScanForUnitFrames(delay)
end

for authors to have a bit more control over expected frames with regards to edge cases?

Indeed, good suggestion, i added lib.ScanForUnitFrames so you can trigger a scan when you want, but it's important to be aware that the cache won't be updated on the same frame this function is called.

You need to register a callback to "GETFRAME_REFRESH", "FRAME_UNIT_UPDATE", or "FRAME_UNIT_REMOVED" that will trigger when scan is finished, if a scan is already in progress when you call ScanForUnitFrames an other one will be done after.

I need to update the README with recent changes to make the lib use coroutine done