Do I glue the yellow dwv test cap?

I have these yellow knock out test caps for my waste lines.. They seem to fit pretty snugly.. Are they supposed to be glued in to handle the water test? If so, then why are the called knock out? Or can you actually remove them after the test even if they have been glued?? Or do I need to plan to cut off the ends of my pipes where the caps are installed?

Thanks?

caps

They MUST be glued or they will just pop off. They are called "knock outs" because that is what you do to them after the test. You "knock out" the center of them before you glue a fitting onto the pipe.

Yeah, we just had one pop off that wasnt glued very well. Make sure its pushed down as far as possible. We used and MJ clamp/cast iron cap after that knock out cap popped off.