verifySetContents(set, EMPTY_COLLECTION);
  }

  public void testNewTreeSetEmpty() {
    TreeSet<Integer> set = Sets.newTreeSet();
    verifySortedSetContents(set, EMPTY_COLLECTION, null);
  }

  public void testNewTreeSetEmptyDerived() {
    TreeSet<Derived> set = Sets.newTreeSet();
    assertTrue(set.isEmpty());
    set.add(new Derived("foo"));
    set.add(new Derived("bar"));

    return generateTreeSet(freshElement);
  }

  @Generates
  static <E extends Comparable<? super E>> TreeSet<E> generateTreeSet(E freshElement) {
    TreeSet<E> set = Sets.newTreeSet();
    set.add(freshElement);
    return set;
  }

  @Generates
  static <E extends Comparable<? super E>> ImmutableSortedSet<E> generateImmutableSortedSet(

  }

  /**
   * {@inheritDoc}
   *
   * <p>Creates an empty {@code TreeSet} for a collection of values for one key.
   *
   * @return a new {@code TreeSet} containing a collection of values for one key
   */
  @Override
  SortedSet<V> createCollection() {
    return new TreeSet<>(valueComparator);
  }

  @Override
  Collection<V> createCollection(@ParametricNullness K key) {

            new TestStringSortedSetGenerator() {
              @Override
              public SortedSet<String> create(String[] elements) {
                return new TreeSet<>(MinimalCollection.of(elements));
              }
            })
        .named("TreeSet, natural")
        .withFeatures(
            SetFeature.GENERAL_PURPOSE,
            CollectionFeature.SERIALIZABLE,
            CollectionFeature.KNOWN_ORDER,

   * use the {@code TreeSet} constructor directly, taking advantage of <a
   * href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
   *
   * @return a new, empty {@code TreeSet}
   */
  @SuppressWarnings("rawtypes") // https://github.com/google/guava/issues/989
  public static <E extends Comparable> TreeSet<E> newTreeSet() {
    return new TreeSet<>();
  }

  /**

    return generateTreeSet(freshElement);
  }

  @Generates
  static <E extends Comparable<? super E>> TreeSet<E> generateTreeSet(E freshElement) {
    TreeSet<E> set = Sets.newTreeSet();
    set.add(freshElement);
    return set;
  }

  @Generates
  static <E extends Comparable<? super E>> ImmutableSortedSet<E> generateImmutableSortedSet(

    return asList(elements).iterator();
  }

  // In GWT, java.util.TreeSet throws ClassCastException when the comparator
  // throws it, unlike JDK6.  Therefore, we accept ClassCastException as a
  // valid result thrown by java.util.TreeSet#equals.
  private static void assertNotEqualLenient(TreeSet<?> unexpected, SortedSet<?> actual) {
    try {
      assertThat(actual).isNotEqualTo(unexpected);

   *
   * <p><b>Warning:</b> by definition, this comparator is not <i>consistent with equals</i> (as
   * defined {@linkplain Comparator here}). Avoid its use in APIs, such as {@link
   * TreeSet#TreeSet(Comparator)}, where such consistency is expected.
   *
   * <p>The returned comparator is serializable.
   *
   * <p><b>Java 8+ users:</b> Use the lambda expression {@code (a, b) -> 0} instead (in certain

                NavigableSet<String> innerSet = new TreeSet<>();
                Collections.addAll(innerSet, elements);
                return Collections.checkedNavigableSet(innerSet, String.class);
              }
            })
        .named("checkedNavigableSet/TreeSet, natural")
        .withFeatures(
            SetFeature.GENERAL_PURPOSE,

      new RegularImmutableSortedSet<Object>(
          new TreeSet<Object>((Comparator<Object>) NATURAL_ORDER), false);

  static <E> ImmutableSortedSet<E> emptySet(Comparator<? super E> comparator) {
    checkNotNull(comparator);
    if (NATURAL_ORDER.equals(comparator)) {
      return of();
    } else {
      return new RegularImmutableSortedSet<E>(new TreeSet<E>(comparator), false);
    }
  }