@Test
public void TestAdd() {

    ObserverList<String> list = concurrentListOf();
    assertEquals(0, list.size());
    assertTrue(list.isEmpty());
    list.notifyObservers("1");
    assertResults();
    list.add(Callback("a"));
    assertEquals(1, list.size());
    assertFalse(list.isEmpty());
    list.notifyObservers("2");
    assertResults("a:2");
    list.add(Callback("b"));
    assertEquals(2, list.size());
    assertFalse(list.isEmpty());
    list.notifyObservers("3");
    assertResults("a:3", "b:3");
    list.add(Callback("c"));
    assertEquals(3, list.size());
    assertFalse(list.isEmpty());
    list.notifyObservers("4");
    assertResults("a:4", "b:4", "c:4");
}