code: def test_mean_metric_instance(self):
      metric = metrics.Metric("test")
      out = metrics.mean(metric, dim=10)
      self.assertTrue(isinstance(out, metrics.MetricTree))
      self.assertTrue(isinstance(out.children[0], metrics.ToDict))
      self.assertTrue(isinstance(out.children[0].metric, metrics.Mean))
      self.assertTrue(out.children[0].metric._kwargs["dim"] == 10)
      self.assertTrue(out.children[0].metric.name == "test")
      self.assertTrue(out.root.name == "test")
  
imports: import unittest
  from mock import Mock
  import torchbearer.metrics
  from torchbearer.metrics import default_for_key, lambda_metric, EpochLambda, BatchLambda
label_desc: Use image node_id 9 for calling the TestDecorators obj's underlying member method code with example usage: obj.test_mean_metric_instance() without return types