public void testListenersWithCategoryPlot() {
        CategoryPlot plot = new CategoryPlot();
        CategoryMarker marker1 = new CategoryMarker("X");
        ValueMarker marker2 = new ValueMarker(1.0);
        plot.addDomainMarker(marker1);
        plot.addRangeMarker(marker2);
        EventListener[] listeners1 = marker1.getListeners(
                MarkerChangeListener.class);
        assertTrue(Arrays.asList(listeners1).contains(plot));
        EventListener[] listeners2 = marker1.getListeners(
                MarkerChangeListener.class);
        assertTrue(Arrays.asList(listeners2).contains(plot));
        plot.clearDomainMarkers();
        plot.clearRangeMarkers();
        listeners1 = marker1.getListeners(MarkerChangeListener.class);
        assertFalse(Arrays.asList(listeners1).contains(plot));
        listeners2 = marker1.getListeners(MarkerChangeListener.class);
        assertFalse(Arrays.asList(listeners2).contains(plot));