We’re in the process of finishing up a small sensor implemented with a small 8-pin microcontroller.  As luck would have it, we have 2 spare I/O pins which we put to good use on our prototype board.  We hooked up 2 LEDs to those spare pins. One indicates the sensor was functional by continually blinking.  The other blinks briefly when the sensor gets a message.  This worked great for development, as it gave us immediate feedback as to the state of the sensor.

We’re now using production boards, and due to space constraints, the LEDs are gone.  I am left with a lifeless black blob of plastic with no visual feedback.  No way to see if my baby works. I miss those LEDs.