* @since 19.0 (since 1.0 as constant {@code INVISIBLE})
   */
  @Deprecated
  public static CharMatcher invisible() {
    return Invisible.INSTANCE;
  }

  /**
   * Determines whether a character is single-width (not double-width). When in doubt, this matcher
   * errs on the side of returning {@code false} (that is, it tends to assume a character is
   * double-width).
   *

   *
   * <p>This must be a (2^n)-1 as it is used as a mask.
   */
  static final int DRAIN_THRESHOLD = 0x3F;

  /**
   * Maximum number of entries to be drained in a single cleanup run. This applies independently to
   * the cleanup queue and both reference queues.
   */
  // TODO(fry): empirically optimize this
  static final int DRAIN_MAX = 16;

  // Fields

  /**

    ListenableFuture<?> statusFuture = closingFuture.statusFuture();
    waiter.awaitStarted();
    assertThat(statusFuture.isDone()).isFalse();
    waiter.awaitReturned();
    assertThat(getUninterruptibly(statusFuture)).isNull();
  }

  public void testStatusFuture_failure() throws Exception {
    ClosingFuture<String> closingFuture =
        ClosingFuture.submit(
            waiter.waitFor(

    {
        PomTestWrapper pom = buildPom( "plugin-config-duplicate/dup" );
    }
    */
    @Test
    void testSingleConfigurationInheritance() throws Exception {
        PomTestWrapper pom = buildPom("single-configuration-inheritance");

        assertEquals(2, ((List<?>) pom.getValue("build/plugins[1]/executions[1]/configuration[1]/rules")).size());
        assertEquals(
                "2.0.6",

    return (ImmutableSortedMap<K, V>) NATURAL_EMPTY_MAP;
  }

  /** Returns an immutable map containing a single entry. */
  public static <K extends Comparable<? super K>, V> ImmutableSortedMap<K, V> of(K k1, V v1) {
    return of(Ordering.natural(), k1, v1);
  }

  /** Returns an immutable map containing a single entry. */
  private static <K, V> ImmutableSortedMap<K, V> of(Comparator<? super K> comparator, K k1, V v1) {

    map.put(2, true);
    try {
      Sets.newSetFromMap(map);
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  /** The 0-ary cartesian product is a single empty list. */
  public void testCartesianProduct_zeroary() {
    assertThat(Sets.cartesianProduct()).containsExactly(list());
  }

    return (ImmutableSortedMap<K, V>) NATURAL_EMPTY_MAP;
  }

  /** Returns an immutable map containing a single entry. */
  public static <K extends Comparable<? super K>, V> ImmutableSortedMap<K, V> of(K k1, V v1) {
    return of(Ordering.natural(), k1, v1);
  }

  /** Returns an immutable map containing a single entry. */
  private static <K, V> ImmutableSortedMap<K, V> of(Comparator<? super K> comparator, K k1, V v1) {

      // override .get() (since it is final) and therefore this is equivalent to calling .get()
      // and unpacking the exceptions like we do below (just much faster because it is a single
      // field read instead of a read, several branches and possibly creating exceptions).
      Object v = ((AbstractFuture<?>) future).value;
      if (v instanceof Cancellation) {

      if (!first) {
        sb.append(", ");
      }
      first = false;
      sb.append(iterator.next());
    }
    return sb.append(']').toString();
  }

  /**
   * Returns the single element contained in {@code iterator}.
   *
   * @throws NoSuchElementException if the iterator is empty
   * @throws IllegalArgumentException if the iterator contains multiple elements. The state of the

      if (!first) {
        sb.append(", ");
      }
      first = false;
      sb.append(iterator.next());
    }
    return sb.append(']').toString();
  }

  /**
   * Returns the single element contained in {@code iterator}.
   *
   * @throws NoSuchElementException if the iterator is empty
   * @throws IllegalArgumentException if the iterator contains multiple elements. The state of the