def METHOD_NAME(self):
    """
    Moves child 3 to the first position."""
    response = self.client.post(
        reverse("wagtailadmin_pages:set_page_position", args=(self.child_1.id,))
        + "?position=1"
    )
    self.assertEqual(response.status_code, 200)
    # check if child_1 is the second child page:
    child_slugs = self.index_page.get_children().values_list("slug", flat=True)
    self.assertListEqual(list(child_slugs), ["child-2", "child-1", "child-3"])