code: def _check_result(self, result):
      
      if not isinstance(result, tuple):
        return (FAIL, APIViolationError(
          'Result must be a tuple but '
          'it is {}.'.format(type(result)), result))
  
      if len(result) != 2:
        return (FAIL, APIViolationError(
          'Result must have 2 items, but it '
          'has {}.'.format(len(result)), result))
  
      status, message = result
      # Allow booleans, but there's no way to issue a WARNING
      if isinstance(status, bool):
        # normalize
        status = PASS if status else FAIL
        result = (status, message)
  
      if not isinstance(status, Status):
        return (FAIL, APIViolationError(
          'Result item `status` must be an instance of '
          'Status, but it is {} a {}.'.format(status, type(status)), result))
  
      return result
docs: Check that the check returned a well formed result:
            a tuple (<Status>, message)
  
          A boolean Status is allowd and will be transformed to:
          True <Status: PASS>, False <Status: FAIL>
  
         Checks will be implemented by other parties. This is to
         help implementors creating good checks, to spot erroneous
         implementations early and to make it easier to handle
         the results tuple.