// effect on them, but can establish the function->gradient relationship
// between them if `func` does not already have a gradient. If `func` already
// has a gradient different from `grad`, an error is returned.
//
// `func` must not be null.
// If `grad` is null and `func` is not in `g`, `func` is added without a
// gradient.
// If `grad` is null and `func` is in `g`, TF_GraphCopyFunction is a noop.

  // Cannot change gradient
  TF_GraphCopyFunction(host_graph_, func_, grad_func1, s_);
  ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
  TF_GraphCopyFunction(host_graph_, func_, grad_func2, s_);
  EXPECT_EQ(TF_INVALID_ARGUMENT, TF_GetCode(s_));
  EXPECT_EQ(string("Cannot assign gradient function 'MyGrad2' to 'MyFunc' "
                   "because it already has gradient function 'MyGrad1'"),

    string expected_msg =
        "No gradient defined for op: TestOpWithNoGradient. Please see "
        "https://www.tensorflow.org/code/"
        "tensorflow/cc/gradients/README.md"
        " for instructions on how to add C++ gradients.";
    EXPECT_EQ(expected_msg, TF_Message(s_));
  }

  // Run the graph and ensure that the gradient values are as expected.

        "//tensorflow/c/eager:tfe_context_internal",
        "//tensorflow/c/eager:tfe_op_internal",
        "//tensorflow/c/eager:tfe_tensorhandle_internal",
        "//tensorflow/c/experimental/gradients",
        "//tensorflow/c/experimental/gradients/tape",
        "//tensorflow/c/experimental/next_pluggable_device:c_api",
        "//tensorflow/c/experimental/ops",
        "//tensorflow/c:c_api_experimental",