cationTest(t, scroller,
                              /*aligned_elements_x=*/[],
                              /*aligned_elements_y=*/[box(1), box(2)],
                              /*axis=*/ "y",
                              /*expected_target_x=*/null,
                              /*expected_target_y=*/box(2));

        // Box 3 should be selected as the target in the x axis despite Box 1's
        // being a common target in both axes because Box 3 is nested within
        // Box 1.
        await runScr