@Test public void testUnregisterOnBackStackChangeListenerNotRegistered() {

	// Arrange:
	final FragmentActivity activity = Robolectric.buildActivity(TestCompatActivity.class).create().start().resume().get();
	final FragmentController controller = new FragmentController(activity.getSupportFragmentManager());
	final FragmentController.OnBackStackChangeListener mockListener = mock(FragmentController.OnBackStackChangeListener.class);
	// Act:
	// Only ensure that un-registering not registered listener does not cause any troubles.
	controller.unregisterOnBackStackChangeListener(mockListener);
}