We have all had difficulty testing diodes in-circuit. Most DMM’s have a diode Vf function that measures forward drop, but what is the normal voltage drop?

Diodes whose reverse-breakdown characteristics are controlled precisely during manufacture are called as Zener diodes and are intended specifically for operation in the reverse breakdown mode ...

The diode’s fast switching action, as well as the simplicity and economy of the circuit, are attractive. Figure 6 illustrates a common implementation of ESD diodes at the terminals of an IC.

This ingenious LED Probe from [David] packs a lot of useful features into a simple, easy-to-implement circuit. Most multimeters have a diode test function that can be used to check LEDs; however ...