public void testHashcode() {
        StackedBarRenderer3D r1 = new StackedBarRenderer3D();
        StackedBarRenderer3D r2 = new StackedBarRenderer3D();
        assertTrue(r1.equals(r2));
        int h1 = r1.hashCode();
        int h2 = r2.hashCode();
        assertEquals(h1, h2);