Assuming you're on Windows and they're all epub (basically zip) files, what I'd do is:
- find all epub using Windows Explorer
- select all (Ctrl+A) then right click
- 7-Zip -> Test archive
Obviously,
7-Zip needs to be installed and
Test archive needs to be added to the context menu.
On Linux, I'm sure there's some way to do something similar natively via shell script. Dunno about Mac.