public void testConcatUnmodifiable() {
    new IteratorTester<Integer>(
        5, UNMODIFIABLE, asList(1, 2), IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat(
            asList(1).iterator(), Arrays.<Integer>asList().iterator(), asList(2).iterator());
      }
    }.test();
  }

  public void testConcatPartiallyAdvancedSecond() {

   *     ImmutableSetMultimap.<Character, Character>builder()
   *         .putAll('b', Arrays.asList('a', 'n', 'a', 'n', 'a'))
   *         .putAll('a', Arrays.asList('p', 'p', 'l', 'e'))
   *         .putAll('c', Arrays.asList('a', 'r', 'r', 'o', 't'))
   *         .putAll('a', Arrays.asList('s', 'p', 'a', 'r', 'a', 'g', 'u', 's'))
   *         .putAll('c', Arrays.asList('h', 'e', 'r', 'r', 'y'))
   *         .build();
   *

   * ordering.
   *
   * @throws NullPointerException if any element is null
   */
  public static <E extends Comparable<? super E>> ImmutableSortedMultiset<E> of(E e1, E e2) {
    return copyOf(Ordering.natural(), Arrays.asList(e1, e2));
  }

  /**
   * Returns an immutable sorted multiset containing the given elements sorted by their natural
   * ordering.
   *
   * @throws NullPointerException if any element is null
   */

   *         .putAll('b', Arrays.asList('a', 'n', 'a', 'n', 'a'))
   *         .putAll('a', Arrays.asList('p', 'p', 'l', 'e'))
   *         .putAll('c', Arrays.asList('a', 'r', 'r', 'o', 't'))
   *         .putAll('a', Arrays.asList('s', 'p', 'a', 'r', 'a', 'g', 'u', 's'))
   *         .putAll('c', Arrays.asList('h', 'e', 'r', 'r', 'y'))
   *         .build();
   * }
   * }</pre>
   *

         */
        return requireNonNull(element);
      }
    };
  }

  @LazyInit @CheckForNull private transient ImmutableList<E> asList;

  @Override
  public ImmutableList<E> asList() {
    ImmutableList<E> result = asList;
    return (result == null) ? asList = super.asList() : result;
  }

  @Override
  public boolean contains(@CheckForNull Object object) {
    return count(object) > 0;
  }

  @Override
  public abstract UnmodifiableIterator<E> iterator();

  @LazyInit @RetainedWith @CheckForNull private transient ImmutableList<E> asList;

  @Override
  public ImmutableList<E> asList() {
    ImmutableList<E> result = asList;
    return (result == null) ? asList = createAsList() : result;
  }

  ImmutableList<E> createAsList() {
    return ImmutableList.asImmutableList(toArray());
  }

  /*

            .named("ImmutableMap.values, unhashable")
            .createTestSuite());

    suite.addTest(
        ListTestSuiteBuilder.using(new ImmutableMapKeyListGenerator())
            .named("ImmutableMap.keySet.asList")
            .withFeatures(
                CollectionSize.ANY,
                CollectionFeature.SERIALIZABLE,
                CollectionFeature.REJECTS_DUPLICATES_AT_CREATION,

    if (elements instanceof ImmutableCollection) {
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList();
      return list.isPartialView() ? ImmutableList.<E>asImmutableList(list.toArray()) : list;
    }
    return construct(elements.toArray());
  }

  /**

   * deterministic iteration behavior.
   *
   * <p>This method is just a small convenience, either for {@code newHashSet(}{@link Arrays#asList
   * asList}{@code (...))}, or for creating an empty set then calling {@link Collections#addAll}.
   * This method is not actually very useful and will likely be deprecated in the future.
   */

   *
   * <p><b>Note:</b> It is often preferable to represent your data using a collection type, for
   * example using {@link Arrays#asList(Object[])}, making this method unnecessary.
   *
   * <p>The {@code Iterable} equivalent of this method is either {@link Arrays#asList(Object[])},
   * {@link ImmutableList#copyOf(Object[])}}, or {@link ImmutableList#of}.
   */
  @SafeVarargs