Developing a Hardware Test Plan for a Microcontroller - Past Experience
3.3V for power.  



Line and Load regulation  
Tolerance of 3.3 V
Ripple
Output current - MCU and other peripherals



  Using GPIO pins to drive some LEDs



LED currents  
GPIO rise time and fall time
Pulse width
PWM Frequency
\$ V_{OH}\$, \$ V_{OL}\$ of the GPIOs



  and send some ports for sending UART,  



baud rate
rise time, fall time
ON time, OFF time
\$ V_{OH}\$, \$ V_{OL}\$, for UART Tx Pin  
\$ V_{IH}\$, \$ V_{IL}\$ for Rx  



  LIN signals.  



Timing and voltage levels as per LIN protocol. similar to UART 
Tolerance and worst case bus voltages from external device
Bus short condition and open condition  



  I'm using 16MHz crystal   



freq. measurement - Direct or via buffered divided output 
Voltage levels   



  If 12 V is from a battery  (inputs from markus)  



Idle system current
Sleep mode current
Active mode current
RF or Full Power ON Mode current
Almost all the above tests at lower limit of the battery
Stable temperature of the board (after running for 8 to 10 hours), especially the power section.



  Power on.  



Reset single timing    
Clock stabilising timing   
Power supply timing