def METHOD_NAME(self, backend):
    root_page = Page.objects.get(id=1)
    page = root_page.add_child(
        instance=SimplePage(title="test", slug="test", content="test")
    )
    # Convert page into a generic "Page" object and add it into the index
    unspecific_page = page.page_ptr
    backend().reset_mock()
    index.insert_or_update_object(unspecific_page)
    # It should be automatically converted back to the specific version
    backend().add.assert_called_with(page)