// TODO: test whether null is supported (create a Feature)
    /**
     * The elements to be returned by future calls to {@code next()}, with the first at the top of
     * the stack.
     */
    final Stack<E> nextElements = new Stack<>();

    /**
     * The elements to be returned by future calls to {@code previous()}, with the first at the top
     * of the stack.
     */

    @DisplayName("ensureTreeConnected caches tree and acquires on each call")
    void testEnsureTreeConnectedCaching() throws CIFSException {
        // Arrange: first ensureTreeConnected comes from pipe
        when(pipe.ensureTreeConnected()).thenReturn(tree);
        when(tree.acquire()).thenReturn(tree); // method returns itself per implementation

        // Act: call twice

 * using a lock, however it is dangerous to dispatch listeners while holding a lock because they
 * might run on the {@code directExecutor()} or be otherwise re-entrant (call back into your
 * object). So it is important to not call {@link #dispatch} while holding any locks. This is why
 * {@link #enqueue} and {@link #dispatch} are 2 different methods. It is expected that the decision

     */
    List<FileNotifyInformation> watch() throws CIFSException;

    /**
     * {@inheritDoc}
     *
     * @see java.util.concurrent.Callable#call()
     */
    @Override
    List<FileNotifyInformation> call() throws CIFSException;

    /**
     * {@inheritDoc}
     *
     * @see java.lang.AutoCloseable#close()
     */
    @Override
    void close() throws CIFSException;

     *     {@link #whenAllComplete(Iterable)} or {@link #whenAllComplete(Iterable)}
     * @throws IllegalStateException if called outside of a call to {@link
     *     CombiningCallable#call(DeferredCloser, Peeker)} or {@link
     *     AsyncCombiningCallable#call(DeferredCloser, Peeker)}
     */
    @ParametricNullness
    public final <D extends @Nullable Object> D getDone(ClosingFuture<D> closingFuture)

    // unless it's actually going to be used; validate() is called for all set method calls, so it
    // needs to be fast.
    // (We could instead generate the message once, when the set is created, but zero is better.)
    if (!validator.get()) {
      throw new IllegalStateException(errorMessage.get());
    }
  }

      // racing addListener calls and addListener calls completing after the future completes.
      Runnable listener = k % 2 == 0 ? collectResultsRunnable : collectResultsTimedGetRunnable;
      allTasks.add(callable(listener));
      allTasks.add(
          new Callable<@Nullable Void>() {
            @Override
            public @Nullable Void call() throws Exception {

      // racing addListener calls and addListener calls completing after the future completes.
      Runnable listener = k % 2 == 0 ? collectResultsRunnable : collectResultsTimedGetRunnable;
      allTasks.add(callable(listener));
      allTasks.add(
          new Callable<@Nullable Void>() {
            @Override
            public @Nullable Void call() throws Exception {

    val request2 = Request.Builder().url(server.url("/")).build()
    val response2 = client.newCall(request2).execute()
    assertThat(response2.body.string()).isEqualTo("def")

    // The HTTP calls should share a single connection.
    assertThat(socksProxy.connectionCount()).isEqualTo(1)
  }

  @Test
  fun proxySelector() {
    server.enqueue(MockResponse.Builder().body("abc").build())

     * @param callable the callable to execute
     * @return the result
     * @throws Exception if execution fails or circuit is open
     */
    public <T> T call(Callable<T> callable) throws Exception {
        return call(callable, null);
    }

    /**
     * Execute a callable through the circuit breaker with fallback
     *
     * @param <T> return type