TFE_CancellationManager* c_mgr = TFE_NewCancellationManager();
  EXPECT_FALSE(TFE_CancellationManagerIsCancelled(c_mgr));

  TFE_CancelCallback callback1;
  callback1.callback = [](void* context) {
    ADD_FAILURE() << "Callback1 should be deregistered.";
  };
  TFE_CancellationToken token1 = TFE_CancellationManagerGetToken(c_mgr);
  EXPECT_TRUE(TFE_CancellationManagerRegisterCallback(c_mgr, token1, &callback1,