public void testClear() {
        XYIntervalSeries s1 = new XYIntervalSeries("S1");
        s1.addChangeListener(this);
        s1.clear();
        assertNull(this.lastEvent);
        assertTrue(s1.isEmpty());
        s1.add(1.0, 2.0, 3.0, 4.0, 5.0, 6.0);
        assertFalse(s1.isEmpty());
        s1.clear();
        assertNotNull(this.lastEvent);
        assertTrue(s1.isEmpty());