This just out: minitest-flash reporter – dull as ditchwater yet useful IMO. It simply calls your personal minitest-flash executable (usually a shell script) to trigger whatever fancy red/green notification you like. Safe to use on team projects as nothing happens unless the executable is present. The README showcases my setup for macOS which flashes the menu bar twice in either red or green along with an optional sound effect (mutable in case your ears have better things to do).