@Test
public void testClear() {

    mItemGroup.addChild(CHILD_1);
    mItemGroup.addChild(CHILD_2);
    mItemGroup.clear();
    assertEquals("Should have 0 child", 0, mItemGroup.getCount());
    verify(mObserver).onItemRangeRemoved(eq(mItemGroup), eq(0), eq(2));
}