}

  void TestGradientsSuccess(bool grad_inputs_provided) {
    TF_Output inputs[2];
    TF_Output outputs[1];
    TF_Output grad_outputs[2];
    TF_Output expected_grad_outputs[2];

    BuildSuccessGraph(inputs, outputs);
    BuildExpectedGraph(grad_inputs_provided, expected_grad_outputs);

    AddGradients(grad_inputs_provided, nullptr, inputs, 2, outputs, 1,
                 grad_outputs);

// only requests schemes that don't exist, first instantiation of the test would
// filter out all the user provided schemes (as they are not registered) but
// subsequent instantiations would return all registered schemes (since the
// vector with the user provided schemes is cleared).
static std::vector<std::string>* GetSchemesFromUserOrEnv() {
  std::vector<std::string>* all_schemes = new std::vector<std::string>;