Iterator<List<Integer>> permutations = permutationSet.iterator();
    assertNextPermutation(Collections.<Integer>emptyList(), permutations);
    assertNoMorePermutations(permutations);
  }

  public void testPermutationSetOneElement() {
    Iterator<List<Integer>> permutations =
        Collections2.permutations(Collections.<Integer>singletonList(1)).iterator();

    private static final ImmutableSet<Integer> INTEGERS = ImmutableSet.of(1, 2, 3, 4);
    private final Iterator<Integer> iterator;

    public IterableIterator() {
      this.iterator = iterator();
    }

    @Override
    public Iterator<Integer> iterator() {
      return INTEGERS.iterator();
    }

    @Override

        @Override
        N visitNext(Deque<Iterator<? extends N>> horizon) {
          Iterator<? extends N> top = horizon.getFirst();
          if (top.hasNext()) {
            return checkNotNull(top.next());
          }
          horizon.removeFirst();
          return null;
        }
      };
    }

    final Iterator<N> breadthFirst(Iterator<? extends N> startNodes) {

  @CollectionSize.Require(SEVERAL)
  public void testRemovePresentConcurrentWithEntrySetIteration() {
    try {
      Iterator<Entry<K, V>> iterator = getMap().entrySet().iterator();
      getMap().remove(k0());
      iterator.next();
      fail("Expected ConcurrentModificationException");
    } catch (ConcurrentModificationException expected) {
      // success
    }
  }

    }
  }

  /**
   * Verifies that an Iterator is unmodifiable.
   *
   * <p>This test only works with iterators that iterate over a finite set.
   */
  public static void assertIteratorIsUnmodifiable(Iterator<?> iterator) {
    while (iterator.hasNext()) {
      iterator.next();
      try {
        iterator.remove();
        fail("Remove on unmodifiable iterator succeeded");

        return new AbstractSet<Entry<String, String>>() {
            @Override
            public Iterator<Entry<String, String>> iterator() {
                Iterator<Entry<Object, Object>> iterator = properties.entrySet().iterator();
                return new Iterator<Entry<String, String>>() {
                    Entry<String, String> next;

                    {
                        advance();

      @Override
      protected Iterator<Integer> newTargetIterator() {
        return newDoubler(1, 2);
      }
    }.test();
  }

  public void testDoubler() {
    Iterable<Integer> doubled =
        new Iterable<Integer>() {
          @Override
          public Iterator<Integer> iterator() {
            return newDoubler(2, 32);
          }
        };

  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testIteratorRemove_unsupported() {
    Iterator<E> iterator = collection.iterator();
    iterator.next();
    try {
      iterator.remove();
      fail("iterator.remove() should throw UnsupportedOperationException");
    } catch (UnsupportedOperationException expected) {
    }
    expectUnchanged();

    assertFalse(underlying.containsKey("b"));

    Iterator<String> keyIterator = keys.iterator();
    keyIterator.next();
    keyIterator.remove();
    assertFalse(underlying.containsKey("c"));

    Collection<String> values = map.values();
    values.remove("4");
    assertFalse(underlying.containsKey("d"));

    Iterator<String> valueIterator = values.iterator();
    valueIterator.next();
    valueIterator.remove();

      return Collections.unmodifiableSet(adjacentNodeValues.keySet());
    } else {
      return new AbstractSet<N>() {
        @Override
        public UnmodifiableIterator<N> iterator() {
          Iterator<NodeConnection<N>> nodeConnections = orderedNodeConnections.iterator();
          Set<N> seenNodes = new HashSet<>();
          return new AbstractIterator<N>() {
            @Override
            @CheckForNull