code: def testTraverserSimpleGraph(self):
      a = nodes.apply_operation(
          _Constant, value="a", label="Constant[a]"
      )
      mock_visitor = mock.MagicMock()
      mock_visitor.visit.side_effect = [("a",)]
      nodes.Traverser(mock_visitor).visit_value_node(a)
      mock_visitor.assert_has_calls(
          [
              mock.call.visit(_Constant("a", "Constant[a]"), ()),
              mock.call.validate_value("a"),
          ]
      )
  
imports: import tensorflow
  from tensorflow_transform import nodes
  from tensorflow_transform import test_case
  from tfx_bsl.types import tfx_namedtuple
label_desc: Use image node_id 5 for calling the NodesTest obj's underlying member method code with example usage: obj.testTraverserSimpleGraph() without return types