The ATtiny85’s Analog Comparator function is perfectly suited for such a tester. One input of the comparator is biased such that there is a 51 ohm resistor between the input and ground.

The IViny features two digital channels and two 10 bit analog channels, just like you’d find in any ATtiny85 project. Power is supplied over USB, and a connection to a computer is provided by V-USB.