This is the explanation how to test the Xmega128a4u breakout board in mass production process.

All pins on the two 20-pin connectors are tested against short circuit or open connection.
The crystal is testet by starting the crystal oscillator.
LEDs are optically tested.
USB connector is testet against short circuit and open connection.
USB ESD protection is testet: BAS70 diode forward voltage, Z-diode breakdown voltage
Reference voltage capacitors are tested.

Xmega128a4u BO Testplan

Testboard