code: def _check_allowed_values(self, parameters):
          
          for key, allowed_values in self.ALLOWED_VALUES:
              self.log([u"Checking allowed values for parameter '%s'", key])
              if key in parameters:
                  value = parameters[key]
                  if value not in allowed_values:
                      self._failed(u"Parameter '%s' has value '%s' which is not allowed." % (key, value))
                      return
          self.log(u"Passed")
docs: Check whether the given parameter value is allowed.
          Log messages into ``self.result``.
  
          :param dict parameters: the given parameters