There is no button on the Super Nova but you can get into test mode the old fashioned way by using the dipswitch on the MVS board. So basically, power down, flip switch 7, power up, voila! You are in test mode.
That is only the hardware test mode... you have no access to the the soft dips (atleast on my two slot) through the dipswitches on the board. You will need to wire the test switch button in.