public void testCloning() {
        ExtendedCategoryAxis a1 = new ExtendedCategoryAxis("Test");
        ExtendedCategoryAxis a2 = null;
        try {
            a2 = (ExtendedCategoryAxis) a1.clone();
        }
        catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        assertTrue(a1 != a2);
        assertTrue(a1.getClass() == a2.getClass());
        assertTrue(a1.equals(a2));
        
        // check independence
        a1.addSubLabel("C1", "ABC");
        assertFalse(a1.equals(a2));
        a2.addSubLabel("C1", "ABC");
        assertTrue(a1.equals(a2));