new ForwardingWrapperTester()
        .testForwarding(
            Deque.class,
            new Function<Deque, Deque<?>>() {
              @Override
              public Deque<?> apply(Deque delegate) {
                return wrap((Deque<?>) delegate);
              }
            });
  }

  private static <T> Deque<T> wrap(Deque<T> delegate) {
    return new ForwardingDeque<T>() {
      @Override

   *
   * @param deque the deque to be wrapped in a synchronized view
   * @return a synchronized view of the specified deque
   * @since 15.0
   */
  @J2ktIncompatible // Synchronized
  public static <E extends @Nullable Object> Deque<E> synchronizedDeque(Deque<E> deque) {
    return Synchronized.deque(deque, null);
  }

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Deque;
import java.util.Iterator;
import org.jspecify.annotations.Nullable;

/**
 * A deque which forwards all its method calls to another deque. Subclasses should override one or
 * more methods to modify the behavior of the backing deque as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Deque;
import java.util.Iterator;
import org.jspecify.annotations.Nullable;

/**
 * A deque which forwards all its method calls to another deque. Subclasses should override one or
 * more methods to modify the behavior of the backing deque as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *

     */
    abstract @Nullable N visitNext(Deque<Iterator<? extends N>> horizon);
  }

  /** 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

    new ForwardingWrapperTester()
        .testForwarding(
            Deque.class,
            new Function<Deque, Deque<?>>() {
              @Override
              public Deque<?> apply(Deque delegate) {
                return wrap((Deque<?>) delegate);
              }
            });
  }

  private static <T> Deque<T> wrap(Deque<T> delegate) {
    return new ForwardingDeque<T>() {
      @Override

   *
   * @param deque the deque to be wrapped in a synchronized view
   * @return a synchronized view of the specified deque
   * @since 15.0
   */
  @J2ktIncompatible // Synchronized
  public static <E extends @Nullable Object> Deque<E> synchronizedDeque(Deque<E> deque) {
    return Synchronized.deque(deque, null);
  }

import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.UncheckedIOException;
import java.io.Writer;
import java.util.Deque;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

  protected Deque<String> create() {
    TestDeque<String> inner = new TestDeque<>();
    Deque<String> outer = Synchronized.deque(inner, inner.mutex);
    outer.add("foo"); // necessary because we try to remove elements later on
    return outer;
  }

  private static final class TestDeque<E> implements Deque<E> {
    private final Deque<E> delegate = new LinkedList<>();

  protected Deque<String> create() {
    TestDeque<String> inner = new TestDeque<>();
    Deque<String> outer = Synchronized.deque(inner, inner.mutex);
    outer.add("foo"); // necessary because we try to remove elements later on
    return outer;
  }

  private static final class TestDeque<E> implements Deque<E> {
    private final Deque<E> delegate = new LinkedList<>();