public synchronized boolean isEmpty() {
        return this.layersList.isEmpty();
    }
@Test
    public void isEmptyTest() {
        Layers layers = new Layers(new DummyRedrawer(), new DisplayModel());
        Assert.assertTrue(layers.isEmpty());

        layers.add(new DummyLayer());
        Assert.assertFalse(layers.isEmpty());

        layers.clear();
        Assert.assertTrue(layers.isEmpty());
    }