self._mock_download_url_to_tempfileobj(self.release_filepath) function changes the download_url_to_tempfileobj function. the modified download function doesn't need required length and required hashes any more. it just simply reads the file of given path and writes it to temporary file.
When _update_metadata is called, the fileinfo parameter  is just passed for download function.  In this case, the download function doesn't need it  so the _update_metadata doesn't  either.