code: def test_string(self):
      root = Metric("test")
      tree = MetricTree(root)
      self.assertEqual(str(root), str(tree))
  
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 TestMetricTree obj's underlying member method code with example usage: obj.test_string() without return types