@Override
  protected abstract Deque<E> delegate();

  @Override
  public void addFirst(@ParametricNullness E e) {
    delegate().addFirst(e);
  }

  @Override
  public void addLast(@ParametricNullness E e) {
    delegate().addLast(e);
  }

  @Override
  public Iterator<E> descendingIterator() {
    return delegate().descendingIterator();
  }

  @Override
  @ParametricNullness
  public E getFirst() {

      this.stack = new ArrayDeque<>();
      stack.addLast(expand(root));
    }

    @Override
    @CheckForNull
    protected T computeNext() {
      while (!stack.isEmpty()) {
        PostOrderNode<T> top = stack.getLast();
        if (top.childIterator.hasNext()) {
          T child = top.childIterator.next();
          stack.addLast(expand(child));
        } else {
          stack.removeLast();

    @Override
    public void addFirst(E e) {
      assertTrue(Thread.holdsLock(mutex));
      delegate.addFirst(e);
    }

    @Override
    public void addLast(E e) {
      assertTrue(Thread.holdsLock(mutex));
      delegate.addLast(e);
    }

    @Override
    public boolean offerFirst(E e) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.offerFirst(e);
    }

  /** Poor man's method reference for {@code Deque::addFirst} and {@code Deque::addLast}. */
  private enum InsertionOrder {
    FRONT {
      @Override
      <T> void insertInto(Deque<T> deque, T value) {
        deque.addFirst(value);
      }
    },
    BACK {
      @Override
      <T> void insertInto(Deque<T> deque, T value) {
        deque.addLast(value);
      }
    };

    @Override
    public void addFirst(E e) {
      assertTrue(Thread.holdsLock(mutex));
      delegate.addFirst(e);
    }

    @Override
    public void addLast(E e) {
      assertTrue(Thread.holdsLock(mutex));
      delegate.addLast(e);
    }

    @Override
    public boolean offerFirst(E e) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.offerFirst(e);
    }

  @Override
  protected abstract Deque<E> delegate();

  @Override
  public void addFirst(@ParametricNullness E e) {
    delegate().addFirst(e);
  }

  @Override
  public void addLast(@ParametricNullness E e) {
    delegate().addLast(e);
  }

  @Override
  public Iterator<E> descendingIterator() {
    return delegate().descendingIterator();
  }

  @Override
  @ParametricNullness
  public E getFirst() {

    @Override
    public void addFirst(E e) {
      synchronized (mutex) {
        delegate().addFirst(e);
      }
    }

    @Override
    public void addLast(E e) {
      synchronized (mutex) {
        delegate().addLast(e);
      }
    }

    @Override
    public boolean offerFirst(E e) {
      synchronized (mutex) {
        return delegate().offerFirst(e);
      }
    }

            .createTestSuite());
    suite.addTest(filterSuite());
    suite.addTest(transformSuite());
    return suite;
  }

  static TestSuite filterSuite() {
    TestSuite suite = new TestSuite("Filter");
    suite.addTest(filterMapSuite());
    suite.addTest(filterBiMapSuite());
    suite.addTest(filterSortedMapSuite());
    suite.addTest(filterNavigableMapSuite());
    return suite;
  }

    TestSuite suite = new TestSuite();

    // Not testing rowKeySet() or columnKeySet() of Table.transformValues()
    // since the transformation doesn't affect the row and column key sets.

    suite.addTest(
        SetTestSuiteBuilder.using(
                new TestStringSetGenerator() {
                  @Override
                  protected Set<String> create(String[] elements) {

    TestSuite suite = new TestSuite();
    suite.addTest(testsForArrayDeque());
    suite.addTest(testsForLinkedList());
    suite.addTest(testsForArrayBlockingQueue());
    suite.addTest(testsForCheckedQueue());
    suite.addTest(testsForConcurrentLinkedDeque());
    suite.addTest(testsForConcurrentLinkedQueue());
    suite.addTest(testsForLinkedBlockingDeque());
    suite.addTest(testsForLinkedBlockingQueue());