@Test
public void addToTop() {

    Object obj = new Object();
    layerHash.addToTop(obj, obj);
    assertEquals(obj, layerHash.getTop());
    assertEquals(obj3, layerHash.getKeysAsList().get(0));
    assertEquals(obj2, layerHash.getKeysAsList().get(1));
    assertEquals(obj1, layerHash.getKeysAsList().get(2));
    assertEquals(obj, layerHash.getKeysAsList().get(3));
}