How to test bipolar linear integrated circuit (voltage detector) using a DMM
First measure the resistance between the output and ground when the device is not powered, it should be open circuit, 

Next part would be with the board powered, measure the output, it should not be pulled to ground if it thinks the devices power rail is good.

I would recommend something like a pin or needle to push through the coating to the pins, if the pin is small enough it will self seal after removal.