}

  @Override
  protected <E extends Comparable<? super E>> Set<E> copyOf(Iterator<? extends E> elements) {
    return ImmutableSet.copyOf(elements);
  }

  public void testCreation_allDuplicates() {
    ImmutableSet<String> set = ImmutableSet.copyOf(Lists.newArrayList("a", "a"));
    assertTrue(set instanceof SingletonImmutableSet);
    assertEquals(Lists.newArrayList("a"), new ArrayList<>(set));
  }