protected void addModel(EpoxyModel<?> modelToAdd) {
    int initialSize = models.size();

    pauseModelListNotifications();
    models.add(modelToAdd);
    resumeModelListNotifications();

    notifyItemRangeInserted(initialSize, 1);
  }
@Test
  public void testAddModel() {
    testAdapter.addModel(new TestModel());
    verify(observer).onItemRangeInserted(0, 1);
    assertEquals(1, testAdapter.models.size());

    testAdapter.addModel(new TestModel());
    verify(observer).onItemRangeInserted(1, 1);
    assertEquals(2, testAdapter.models.size());
    checkDifferState();
  }