TF_Graph* graph = TF_NewGraph();
  TF_Buffer* buffer = TF_NewBuffer();

  TF_GraphGetOpDef(graph, "Add", buffer, status);
  ASSERT_EQ(TF_OK, TF_GetCode(status));
  const OpDef* expected_op_def;
  TF_ASSERT_OK(OpRegistry::Global()->LookUpOpDef("Add", &expected_op_def));
  std::string expected_serialized;
  expected_op_def->SerializeToString(&expected_serialized);

    graph optimizer options are now specified via
    `GraphOptions.OptimizerOptions`.
*   `ASSERT_OK` / `EXPECT_OK` macros conflicted with external projects, so they
    were renamed `TF_ASSERT_OK`, `TF_EXPECT_OK`. The existing macros are
    currently maintained for short-term compatibility but will be removed.
*   The non-public `nn.rnn` and the various `nn.seq2seq` methods now return just