public void testGetSetAlpha() {
        // we use ValueMarker for the tests, because we need a concrete 
        // subclass...
        ValueMarker m = new ValueMarker(1.1);
        m.addChangeListener(this);
        this.lastEvent = null;
        assertEquals(0.8f, m.getAlpha(), EPSILON);
        m.setAlpha(0.5f);
        assertEquals(0.5f, m.getAlpha(), EPSILON);
        assertEquals(m, this.lastEvent.getMarker());