I having a hard time figuring out how to properly test an optocoupler. I think I may have fried it by applying 5volts in circuit with positive=anode and negative=cathode. I wasn’t getting any change in resistance across the emitter and collector proportional to the change in input voltage. I then removed it from the circuit and used a 330ohm resistor to limit the current from the bench dc power supply and still am getting nothing
Finally I used the diode function on my meter across the led portion of the optocoupler and I am not getting any diode voltage drop. Here is a data sheet
https://www.vishay.com/docs/83606/cny17.pdf

 

The diode max is 60ma, so you need a suitable resistor in series to limit less than this.
You probably fried it with the first test.

 

I think I may have fried it ...

Sounds like it.

 

Test set up.