code: def test_eval(self):
      root = Metric("test")
      root.eval = Mock()
      leaf = Metric("test")
      leaf.eval = Mock()
  
      tree = MetricTree(root)
      tree.add_child(leaf)
  
      tree.eval()
  
      self.assertEqual(root.eval.call_count, 1)
      self.assertEqual(leaf.eval.call_count, 1)
  
imports: import unittest
  from mock import Mock
  from torchbearer.metrics import MetricList, Metric, MetricTree, AdvancedMetric
label_desc: Use image node_id 5 for calling the TestMetricTree obj's underlying member method code with example usage: obj.test_eval() without return types