code: def compute_diff(test_case, test_case_result, output_file, base_file_path):
      
      with open(File.file_path(base_file_path, test_case.expected.sha1)) as fp:
          expected_output = fp.read()
      actual_output = ''
      if os.path.isfile(output_file):
          with open('tc_{0}'.format(test_case.id)) as fp:
              actual_output = fp.read()
      unit = Diff(expected_output, actual_output)
      if not unit.outputs_match():
          test_case_result.diff = File.fetch_or_create(pickle.dumps(unit),
                                                       base_file_path)
          return False
      return True
docs: Associate the diff (if exists) with the TestCaseResult.
  
      Return whether or not the outputs match.