code: def get_metric_values(self, group_name):
          
          if group_name not in self._metric_values:
              raise ValueError("Metric values for this group name do not "
                               "exist: {}".format(group_name))
          return self._metric_values[group_name]
docs: Get the faked metric values for a metric group, by its metric group
          name.
  
          The result includes all metric object values added earlier for that
          metric group name, using
          :meth:`~zhmcclient.FakedMetricsContextManager.add_metric_object_values`
          i.e. the metric values for all resources and all points in time that
          were added.
  
          Parameters:
  
            group_name (:term:`string`): Name of the metric group.
  
          Returns:
  
            iterable of :class:`~zhmclient.FakedMetricObjectValues`: The metric
              values for that metric group, in the order they had been added.
  
          Raises:
  
            ValueError: Metric values for this group name do not exist.