dons:
I just pushed a patch fully testing, via QuickCheck properties, the builtin tall layout, and how it handles messages. That code is fully covered now.
To layout authors, using pureLayout and pureMessage, have a poke around Properties.hs , to get an idea how to generate random window manager states, apply your layouts to them, and then to test their behaviour with random message events.
Oh, also, there's a built in script now for getting code coverage details from the QuickCheck suite (see tests/coverage.hs). Note, these are the parts of the code tested on every commit -- you can't commit unless the entire suite runs to success. Results here: http://galois.com/~dons/tmp/hpc_index.html StackSet.hs, where most of the logic is, is fully covered, Layout.hs starting. Should help drive testing. -- Don