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.

Testboard

All the functions are tested by the passive testboard. "Passive" means there is no processor on the board. The testprocess is done by the Xmega Breakout Board.