I am not sure what you would like to see added.

in zipimport.c:

"- _zip_directory_cache: a dict, mapping archive paths to zip directory
  info dicts, as used in zipimporter._files.
"

while there are no direct test, Lib/test/test_zipimport.py covers it
becauseit is used when you instanciate a zipimport class.

would you like to see a section explaining how it works at 
http://docs.python.org/library/zipimport.html ?