return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
  }

  /**
   * Provides a lexicographical comparator implementation; either a Java implementation or a faster
   * implementation based on {@link Unsafe}.
   *
   * <p>Uses reflection to gracefully fall back to the Java implementation if {@code Unsafe} isn't
   * available.
   */
  @VisibleForTesting
  static class LexicographicalComparatorHolder {

    return LexicographicalComparatorHolder.PureJavaComparator.INSTANCE;
  }

  /**
   * Provides a lexicographical comparator implementation; either a Java implementation or a faster
   * implementation based on {@link Unsafe}.
   *
   * <p>Uses reflection to gracefully fall back to the Java implementation if {@code Unsafe} isn't
   * available.
   */
  @VisibleForTesting
  static class LexicographicalComparatorHolder {

              @Override
              public String pendingToString() {
                throw new RuntimeException("I'm a misbehaving implementation");
              }
            }.toString())
        .matches(
            "[^\\[]+\\[status=PENDING, info=\\[Exception thrown from implementation: "
                + "class java.lang.RuntimeException\\]\\]");
  }

  public void testCompletionFinishesWithDone() {

      super("Returned value '" + actual + "' not found. Remaining elements: " + expected);
    }

    private static final long serialVersionUID = 0;
  }

  /**
   * Quasi-implementation of {@link ListIterator} that works from a list of elements and a set of
   * features to support (from the enclosing {@link AbstractIteratorTester} instance). Instead of

              @Override
              public String pendingToString() {
                throw new RuntimeException("I'm a misbehaving implementation");
              }
            }.toString())
        .matches(
            "[^\\[]+\\[status=PENDING, info=\\[Exception thrown from implementation: "
                + "class java.lang.RuntimeException\\]\\]");
  }

  public void testCompletionFinishesWithDone() {

      }
    };
  }

  /**
   * Returns a "nefarious" map entry with the specified key and value, meaning an entry that is
   * suitable for testing that map entries cannot be modified via a nefarious implementation of
   * equals. This is used for testing unmodifiable collections of map entries; for example, it
   * should not be possible to access the raw (modifiable) map entry via a nefarious equals method.
   */

          && hashCodeInsensitiveToArgReference(
              factory, args, i, generateDummyArg(param, newFreshValueGenerator()))) {
        // If the implementation uses identityHashCode(), referential equality is
        // probably intended. So no point in using an equal-but-different factory argument.
        // We check twice to avoid confusion caused by accidental hash collision.

      super("Returned value '" + actual + "' not found. Remaining elements: " + expected);
    }

    private static final long serialVersionUID = 0;
  }

  /**
   * Quasi-implementation of {@link ListIterator} that works from a list of elements and a set of
   * features to support (from the enclosing {@link AbstractIteratorTester} instance). Instead of

      }
    };
  }

  /**
   * Returns a "nefarious" map entry with the specified key and value, meaning an entry that is
   * suitable for testing that map entries cannot be modified via a nefarious implementation of
   * equals. This is used for testing unmodifiable collections of map entries; for example, it
   * should not be possible to access the raw (modifiable) map entry via a nefarious equals method.
   */

          && hashCodeInsensitiveToArgReference(
              factory, args, i, generateDummyArg(param, newFreshValueGenerator()))) {
        // If the implementation uses identityHashCode(), referential equality is
        // probably intended. So no point in using an equal-but-different factory argument.
        // We check twice to avoid confusion caused by accidental hash collision.