docs: def compare_fetch_with_fs(self):
          """Compares the fetch entries with the files actually
             in the payload, and returns a list of all the files
             that still need to be fetched.
          """
  
          files_on_fs = set(self.payload_files())
          files_in_fetch = set(self.files_to_be_fetched())
  
          return list(files_in_fetch - files_on_fs)