The Pertronix units are an electronic switch. As long as you are dealing with the original Pertronix (and not Ignitor-II), you can bench test the units both on and off the car.
You can rig up a simple test circuit with any 12V indicator bulb you happen to have. Solder some leads to it. Using a 12V battery charger as a power supply, connect the red battery charger lead and one side of the test lamp to the "RED" Pertronix wire. Connect the other side of the test lamp to the Pertronix "BLACK" wire. Connect the black battery charger lead to the mounting foot of the Pertronix module.
With the battery charger powered up, move the target ring for the Pertronix unit slowly in front of the Pertronix module. As the magnets in the target ring go past the sensor in the module, the test lamp should turn on and off.