code: def test_single_metric(self):
      for m in self.test_metrics:
          self._run_test(self.train, self.test, m)
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import unittest
  import turicreate
  from turicreate.toolkits._main import ToolkitError
  import random
label_desc: Use image node_id 6 for calling the TreeRegressionTrackingMetricsTest obj's underlying member method code with example usage: obj.test_single_metric() without return types