SettableFuture<Integer> future = SettableFuture.create();
    assertTrue(future.set(42));
    // Later attempts to set the future should return false.
    assertFalse(future.set(23));
    assertFalse(future.setException(new Exception("bar")));
    assertFalse(future.setFuture(SettableFuture.<Integer>create()));
    // Check that the future has been set properly.
    assertTrue(future.isDone());
    assertFalse(future.isCancelled());

          }

          @Override
          public void onFailure(Throwable t) {
            failureCalls[0]++;
          }
        };
    addCallback(future, callback, directExecutor());
    future.set(result);
    assertEquals(result, future.get());
    assertThat(successCalls[0]).isEqualTo(1);
    assertThat(failureCalls[0]).isEqualTo(0);
  }

  public void testOnSuccessThrowsError() throws Exception {

  static <V extends @Nullable Object, X extends Exception> V getChecked(
      Future<V> future, Class<X> exceptionClass) throws X {
    return getChecked(bestGetCheckedTypeValidator(), future, exceptionClass);
  }

  /** Implementation of {@link Futures#getChecked(Future, Class)}. */
  @CanIgnoreReturnValue
  @VisibleForTesting
  @ParametricNullness
  static <V extends @Nullable Object, X extends Exception> V getChecked(

    checkNotNull(timeoutUnit);
    checkPositiveTimeout(timeoutDuration);

    Future<T> future = executor.submit(callable);

    try {
      return amInterruptible
          ? future.get(timeoutDuration, timeoutUnit)
          : getUninterruptibly(future, timeoutDuration, timeoutUnit);
    } catch (InterruptedException e) {
      future.cancel(true);
      throw e;
    } catch (ExecutionException e) {

  /** Invoked with the result of the {@code Future} computation when it is successful. */
  void onSuccess(@ParametricNullness V result);

  /**
   * Invoked when a {@code Future} computation fails or is canceled.
   *
   * <p>If the future's {@link Future#get() get} method throws an {@link ExecutionException}, then
   * the cause is passed to this method. Any other thrown object is passed unaltered.
   */

 * result. (If you want such access, you may prefer {@link Futures#addCallback
 * Futures.addCallback}.) Still, direct {@code addListener} calls are occasionally useful:
 *
 * {@snippet :
 * final String name = ...;
 * inFlight.add(name);
 * ListenableFuture<Result> future = service.query(name);
 * future.addListener(new Runnable() {
 *   public void run() {

 * result. (If you want such access, you may prefer {@link Futures#addCallback
 * Futures.addCallback}.) Still, direct {@code addListener} calls are occasionally useful:
 *
 * {@snippet :
 * final String name = ...;
 * inFlight.add(name);
 * ListenableFuture<Result> future = service.query(name);
 * future.addListener(new Runnable() {
 *   public void run() {

          }

          @Override
          public void onFailure(Throwable t) {
            failureCalls[0]++;
          }
        };
    addCallback(future, callback, directExecutor());
    future.set(result);
    assertEquals(result, future.get());
    assertThat(successCalls[0]).isEqualTo(1);
    assertThat(failureCalls[0]).isEqualTo(0);
  }

  public void testOnSuccessThrowsError() throws Exception {

    assertFalse(future.isCancelled());

    ExecutorService executor = newSingleThreadExecutor();

    try {
      Future<Boolean> getResult = executor.submit(() -> future.get());

      // Release the future value.
      latch.countDown();

      assertTrue(getResult.get(10, SECONDS));
    } finally {
      executor.shutdownNow();
    }

    assertTrue(future.isDone());

    }
  }

  private enum Result {
    SUCCESS(immediateFuture(new Object())),
    FAILURE(immediateFailedFuture(new Exception()));

    final Future<Object> future;

    Result(Future<Object> result) {
      this.future = result;
    }
  }

  private enum ExceptionType {
    CHECKED(IOException.class),
    UNCHECKED(RuntimeException.class);