@Test
  public void testAddAll() {
    IntDoubleLinkedSet set2 = new IntDoubleLinkedSet();
    set2.add(1, 2);
    set.add(0, 1);

    assertEquals(1, set.addAll(set2));
    assertEquals(0, set.addAll(set2));

    assertEquals(3, set.size());
    assertSortedListEquals(set.toArray(), 0, 1, 2);
  }