The easiest way is to setting zlib to None or not import it at all.
Are you suggesting that test_zipfile should be always run with and without zlib to check that everything (except the things that require zlib of course) works in both the cases?
My concern was about that part that handles unconsumed data only, because I didn't see any test in the patch that specifically check it. If there are already tests that checks it, then it's fine, even if it's not possible to test that part without zlib.