// Define the function
  DefineFunction(func_name_, &func_);
  TF_Function* grad_func1;
  TF_Function* grad_func2;
  DefineFunction("MyGrad1", &grad_func1);
  DefineFunction("MyGrad2", &grad_func2);

  // func cannot be null
  TF_GraphCopyFunction(host_graph_, nullptr, func_, s_);
  EXPECT_EQ(TF_INVALID_ARGUMENT, TF_GetCode(s_));