import org.jspecify.annotations.NullUnmarked;

/**
 * Tests for {@link ForwardingCollection}.
 *
 * @author Robert Konigsberg
 * @author Hayward Chan
 * @author Louis Wasserman
 */
@NullUnmarked
public class ForwardingCollectionTest extends TestCase {
  static final class StandardImplForwardingCollection<T> extends ForwardingCollection<T> {
    private final Collection<T> backingCollection;

    throw new AssertionError("should never be called");
  }

  @Override
  Collection<Entry<K, V>> createEntries() {
    return new Entries();
  }

  @WeakOuter
  class Entries extends ForwardingCollection<Entry<K, V>> {
    @Override
    protected Collection<Entry<K, V>> delegate() {
      return Collections2.filter(unfiltered.entries(), entryPredicate());
    }

    @Override

        public boolean retainAll(Collection<?> c) {
          return delegate.keySet().retainAll(c);
        }
      };
    }

    @Override
    public Collection<V> values() {
      return new ForwardingCollection<V>() {
        @Override
        protected Collection<V> delegate() {
          return delegate.values();
        }

        @Override
        public Iterator<V> iterator() {

        public boolean retainAll(Collection<?> c) {
          return delegate.keySet().retainAll(c);
        }
      };
    }

    @Override
    public Collection<V> values() {
      return new ForwardingCollection<V>() {
        @Override
        protected Collection<V> delegate() {
          return delegate.values();
        }

        @Override
        public Iterator<V> iterator() {

 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingMultiset<E extends @Nullable Object> extends ForwardingCollection<E>
    implements Multiset<E> {

  /** Constructor for use by subclasses. */
  protected ForwardingMultiset() {}

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

  @Override

 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingMultiset<E extends @Nullable Object> extends ForwardingCollection<E>
    implements Multiset<E> {

  /** Constructor for use by subclasses. */
  protected ForwardingMultiset() {}

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

  @Override

   */
  @SafeVarargs
  public static <B> Set<List<B>> cartesianProduct(Set<? extends B>... sets) {
    return cartesianProduct(asList(sets));
  }

  private static final class CartesianSet<E> extends ForwardingCollection<List<E>>
      implements Set<List<E>> {
    private final transient ImmutableList<ImmutableSet<E>> axes;
    private final transient CartesianList<E> delegate;

      }
    };
  }

  /** The implementation of {@link Multimaps#unmodifiableEntries}. */
  static class UnmodifiableEntries<K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingCollection<Entry<K, V>> {
    private final Collection<Entry<K, V>> entries;

    UnmodifiableEntries(Collection<Entry<K, V>> entries) {
      this.entries = entries;
    }

    @Override

      }
    };
  }

  /** The implementation of {@link Multimaps#unmodifiableEntries}. */
  static class UnmodifiableEntries<K extends @Nullable Object, V extends @Nullable Object>
      extends ForwardingCollection<Entry<K, V>> {
    private final Collection<Entry<K, V>> entries;

    UnmodifiableEntries(Collection<Entry<K, V>> entries) {
      this.entries = entries;
    }

    @Override