"Bob" wrote

It's the pretty typical 2 outlet type, with the black and red
pushbuttons between the outlets.


How do I test it please:

If I press the black "Test" button in, is the red "Reset" button
supposed to pop-out ?

Yes

If it does, or doesn't, what does this indicate ?

Pops out means OK. Stays in, = junk

As long as both buttons are in (depressed positions), which they are,
should it be working ?

No. It's broke.