You can tap it with a hammer and break it out in bits.
You won't lose the solvent glue joint between the box and pipe.
Help. I installed one of these boxes, and now the drain test cap won't snap off. I twisted the test nib like the directions said, and it snapped off. I just need to remove the test cap on the drain, but fear I may break the solvent weld to the ABS standpipe. Suggestions? Thank you in advance.