TF_Operation* neg = Neg(add, graph, s);
  ASSERT_EQ(TF_OK, TF_GetCode(s)) << TF_Message(s);

  // Serialize to NodeDef.
  NodeDef node_def;
  ASSERT_TRUE(GetNodeDef(neg, &node_def));

  // Validate NodeDef is what we expect.
  EXPECT_TRUE(IsNeg(node_def, "add"));

  // Serialize to GraphDef.
  GraphDef graph_def2;
  ASSERT_TRUE(GetGraphDef(graph, &graph_def2));