The function "open_urlresource" never invalidates its cache. If a file with same name is available in "Lib/test/data/", it is returned. There's a snippet in test_normalization which tries to invalidate the cache, but it fails because it looks in the wrong location. (#7783)
The check argument is any function which receives an open file and return a boolean. For example: - verify the version number on the first line (test_normalization) - calculate the MD5