code: def compare(self, control_result, experimental_result):
          _compare = getattr(self, '_compare', lambda x, y: x == y)
          
          return (
              # Mismatch if only one of the results returned an error, or if
              # different types of errors were returned.
              type(control_result.error) is type(experimental_result.error) and
              _compare(control_result.value, experimental_result.value)
          )
docs: Return true if the results match.