code: def test_train(self):
      my_mock = Metric("test")
      my_mock.train = Mock(return_value=None)
      metric = MetricList([my_mock])
      metric.train()
      self.assertEqual(my_mock.train.call_count, 1)
  
imports: import unittest
  from mock import Mock
  from torchbearer.metrics import MetricList, Metric, MetricTree, AdvancedMetric
label_desc: Use image node_id 7 for calling the TestMetricList obj's underlying member method code with example usage: obj.test_train() without return types