code: def check_for_new_files_in_home(self):
          
          if not self._user:
              return None
          try:
              created_files = set(self._listdir(self._home_dir)).difference(self._home_dir_content)
          except (subprocess.CalledProcessError, IOError):
              # Probably home directory does not exist
              created_files = []
          if created_files:
              logging.warning('The tool created the following files in %s, '
                              'this may influence later runs:\n\t%s',
                              self._home_dir, '\n\t'.join(created_files))
          return created_files
docs: Check that the user account's home directory now does not contain more files than
          when this instance was created, and warn otherwise.
          Does nothing if no user account was given to RunExecutor.
          @return set of newly created files