code: def diff(self, test_id_1, test_id_2, config=None, **kwargs):
      
      output_directory = os.path.join(self._output_directory, 'diff_' + str(test_id_1) + '_' + str(test_id_2))
      if kwargs:
        if 'output_directory' in kwargs.keys():
          output_directory = kwargs['output_directory']
      diff_report = Diff([NaaradReport(self._analyses[test_id_1].output_directory, None),
                          NaaradReport(self._analyses[test_id_2].output_directory, None)],
                         'diff', output_directory, os.path.join(output_directory, self._resource_path),
                         self._resource_path)
      if config:
        naarad.utils.extract_diff_sla_from_config_file(diff_report, config)
      diff_report.generate()
      if diff_report.sla_failures > 0:
        return CONSTANTS.SLA_FAILURE
      if diff_report.status != 'OK':
        return CONSTANTS.ERROR
      return CONSTANTS.OK
docs: Create a diff report using test_id_1 as a baseline
      :param: test_id_1: test id to be used as baseline
      :param: test_id_2: test id to compare against baseline
      :param: config file for diff (optional)
      :param: **kwargs: keyword arguments