public void testAddURLSeries() {
        CustomCategoryURLGenerator g1 = new CustomCategoryURLGenerator();
        // you can add a null list - it would have been better if this
        // required EMPTY_LIST
        g1.addURLSeries(null);
        assertEquals(1, g1.getListCount());
        assertEquals(0, g1.getURLCount(0));

        List list1 = new java.util.ArrayList();
        list1.add("URL1");
        g1.addURLSeries(list1);
        assertEquals(2, g1.getListCount());
        assertEquals(0, g1.getURLCount(0));
        assertEquals(1, g1.getURLCount(1));
        assertEquals("URL1", g1.getURL(1, 0));

        // if we modify the original list, it's best if the URL generator is
        // not affected
        list1.clear();
        assertEquals("URL1", g1.getURL(1, 0));