quick and dirty test harness for xmonad configs
source ./sandbox.sh to enter the harness's sandbox. This sets $HOME to the
test harness directory.
startx -- :1 to launch a xephyr on a (presumed) xmonad config in the usual place
(either ~/.xmonad or ~/.config/xmonad).
source ./sandbox.sh - to exit the sandbox.
there's a zsh-ism buried in sandbox.sh to pop $PATH.
since $HOME is set, you can use custom ghcup, cabal, stack, etc. inside
the sandbox.