const char* name, const char* placeholder,
                                   TF_Operation** op) {
  TF_OperationDescription* desc = TF_NewOperation(graph, "CustomOp", name);
  TF_SetAttrPlaceholder(desc, "index", placeholder);
  *op = TF_FinishOperation(desc, s);
  ASSERT_EQ(TF_OK, TF_GetCode(s)) << TF_Message(s);
  ASSERT_NE(*op, nullptr);
}