code: def testCPU(self):
      ops.reset_default_graph()
      with ops.device("/cpu:0"):
          tfprof_node, run_meta = _run_model()
          self.assertEqual(tfprof_node.children[0].name, "MatMul")
          self.assertGreater(tfprof_node.children[0].exec_micros, 0)
  
      ret = _extract_node(run_meta, "MatMul")
      self.assertEqual(len(ret["cpu:0"]), 1)
  
      ret = _extract_node(run_meta, "MatMul:MatMul")
      self.assertEqual(len(ret), 0)
  
imports: from collections import defaultdict
  from tensorflow.core.protobuf import config_pb2
  from tensorflow.core.protobuf import rewriter_config_pb2
  from tensorflow.python.client import session
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import random_ops
  from tensorflow.python.ops import variables
  from tensorflow.python.platform import test
  from tensorflow.python.profiler import option_builder
  from tensorflow.python.profiler import model_analyzer
  from tensorflow.python.profiler.internal import model_analyzer_testlib
label_desc: Use image node_id 3 for calling the RunMetadataTest obj's underlying member method code with example usage: obj.testCPU() without return types