private final ListenableFuture<V> delegate;

  ForwardingFluentFuture(ListenableFuture<V> delegate) {
    this.delegate = checkNotNull(delegate);
  }

  @Override
  public void addListener(Runnable listener, Executor executor) {
    delegate.addListener(listener, executor);
  }

  @Override
  public boolean cancel(boolean mayInterruptIfRunning) {
    return delegate.cancel(mayInterruptIfRunning);
  }

 * For restrictions, please refer to the documentation of the then() method.
 */
public interface ListenableFuture<V extends @Nullable Object> extends Future<V>, IThenable<V> {
  void addListener(Runnable listener, Executor executor);

  /** Note that this method is not expected to be overridden. */
  @JsMethod
  @Override
  default <R extends @Nullable Object> IThenable<R> then(

    validations:
      required: true

  - type: textarea
    id: what-did-you-do
    attributes:
      label: "What did you do?"
      description: "If possible, provide a recipe for reproducing the error. A complete runnable program is good. A link on [go.dev/play](https://go.dev/play) is best."
    validations:
      required: true

  - type: textarea
    id: actual-behavior
    attributes:
      label: "What did you see happen?"

  @SuppressWarnings("ThreadPriorityCheck") // TODO: b/175898629 - Consider onSpinWait.
  static void awaitWaiting(Thread t) {
    while (true) {
      Thread.State state = t.getState();
      switch (state) {
        case RUNNABLE:
        case BLOCKED:
          Thread.yield();
          break;
        case WAITING:
          return;
        default:
          throw new AssertionError("unexpected state: " + state);
      }

  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingRunnable runnable) {
    return doAssertThrows(
        expectedThrowable,
        () -> {
          runnable.run();
          return null;
        },
        /* userPassedSupplier= */ false);
  }

  private static <T extends Throwable> T doAssertThrows(

  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingRunnable runnable) {
    return doAssertThrows(
        expectedThrowable,
        () -> {
          runnable.run();
          return null;
        },
        /* userPassedSupplier= */ false);
  }

  private static <T extends Throwable> T doAssertThrows(

  }

  @CanIgnoreReturnValue
  static <T extends Throwable> T assertThrows(
      Class<T> expectedThrowable, ThrowingRunnable runnable) {
    return doAssertThrows(
        expectedThrowable,
        () -> {
          runnable.run();
          return null;
        },
        /* userPassedSupplier= */ false);
  }

  private static <T extends Throwable> T doAssertThrows(

      this.exception = exception;
      this.context = context;
    }
  }

  /** Runnable which registers a StringCatcher on an event bus and adds it to a list. */
  private static class Registrator implements Runnable {
    private final EventBus bus;
    private final List<StringCatcher> catchers;

    Registrator(EventBus bus, List<StringCatcher> catchers) {

      this.exception = exception;
      this.context = context;
    }
  }

  /** Runnable which registers a StringCatcher on an event bus and adds it to a list. */
  private static class Registrator implements Runnable {
    private final EventBus bus;
    private final List<StringCatcher> catchers;

    Registrator(EventBus bus, List<StringCatcher> catchers) {

      TrustedListenableFutureTask<Integer> task =
          TrustedListenableFutureTask.create(counter::incrementAndGet);
      CyclicBarrier barrier = new CyclicBarrier(numThreads + 1);
      Runnable wrapper =
          () -> {
            awaitUnchecked(barrier);
            task.run();
            awaitUnchecked(barrier);
          };
      for (int j = 0; j < 10; j++) {