List<E> tail = list.subList(1, size);
    assertTrue(copy.contains(list.get(0)));
    assertTrue(head.contains(list.get(0)));
    assertTrue(tail.contains(list.get(1)));
    // The following assumes all elements are distinct.
    assertTrue(copy.contains(list.get(size - 1)));
    assertTrue(head.contains(list.get(size - 2)));
    assertTrue(tail.contains(list.get(size - 1)));
    assertFalse(head.contains(list.get(size - 1)));

    List<E> tail = list.subList(1, size);
    assertTrue(copy.contains(list.get(0)));
    assertTrue(head.contains(list.get(0)));
    assertTrue(tail.contains(list.get(1)));
    // The following assumes all elements are distinct.
    assertTrue(copy.contains(list.get(size - 1)));
    assertTrue(head.contains(list.get(size - 2)));
    assertTrue(tail.contains(list.get(size - 1)));
    assertFalse(head.contains(list.get(size - 1)));

    //                                                                           =========
    private static final UserInfoDbm _instance = new UserInfoDbm();

    private UserInfoDbm() {
    }

    public static UserInfoDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final RequestHeaderDbm _instance = new RequestHeaderDbm();

    private RequestHeaderDbm() {
    }

    public static RequestHeaderDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

        // Act & Assert
        // unwrap to interface itself should return same instance
        CredentialsInternal unwrapped = creds.unwrap(CredentialsInternal.class);
        assertNotNull(unwrapped, "unwrap to CredentialsInternal returns instance");
        assertSame(creds, unwrapped, "unwrap returns the same object instance");

        // unwrap to unrelated type should return null (use another Credentials implementation)

  /** Creates an empty {@code CompactLinkedHashSet} instance. */
  public static <E extends @Nullable Object> CompactLinkedHashSet<E> create() {
    return new CompactLinkedHashSet<>();
  }

  /**
   * Creates a <i>mutable</i> {@code CompactLinkedHashSet} instance containing the elements of the
   * given collection in the order returned by the collection's iterator.
   *

    //                                                                           =========
    private static final KeyMatchDbm _instance = new KeyMatchDbm();

    private KeyMatchDbm() {
    }

    public static KeyMatchDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

  /**
   * Shortcut for {@code newHasher().putObject(instance, funnel).hash()}. The implementation
   * <i>might</i> perform better than its longhand equivalent, but should not perform worse.
   *
   * @since 14.0
   */
  <T extends @Nullable Object> HashCode hashObject(
      @ParametricNullness T instance, Funnel<? super T> funnel);

  /**

  /**
   * Shortcut for {@code newHasher().putObject(instance, funnel).hash()}. The implementation
   * <i>might</i> perform better than its longhand equivalent, but should not perform worse.
   *
   * @since 14.0
   */
  <T extends @Nullable Object> HashCode hashObject(
      @ParametricNullness T instance, Funnel<? super T> funnel);

  /**

  /** Creates an empty {@code CompactLinkedHashMap} instance. */
  public static <K extends @Nullable Object, V extends @Nullable Object>
      CompactLinkedHashMap<K, V> create() {
    return new CompactLinkedHashMap<>();
  }

  /**
   * Creates a {@code CompactLinkedHashMap} instance, with a high enough "initial capacity" that it