I was following this and I ran into something that does not match up on my end..

http://preher-tech.com/documents/optoisolators

Testing the anode and cathode passed but everything including testing it the reverse way I don't see on my end.

I tried the 2nd method and nope still nothing, the 2nd way I assume it would cause the resistance to stop but nope I still see OL on my meter.

 

Putting power to the LED will switch on the transistor.
You need to power to the transistor through a resistor to see it working.

 

Putting power to the LED will switch on the transistor.
You need to power to the transistor through a resistor to see it working.

Turns out my other meter was not supplying enough power to turn the LED on.. but yeah they work fine

 

If your multimeter is powered by a 1.5 V battery, it may not be enough voltage to get the same readings as on the document.