@Override
          protected void doStart() {
            notifyFailed(new IllegalStateException("start failure"));
            notifyStopped(); // This will be a no-op.
          }

          @Override
          protected void doStop() {
            notifyStopped();
          }
        };
    ServiceManager manager = new ServiceManager(asList(a));
    manager.startAsync();

   */
  private static final class NoOpService extends AbstractService {
    @Override
    protected void doStart() {
      notifyStarted();
    }

    @Override
    protected void doStop() {
      notifyStopped();
    }
  }

  /** This is never thrown but only used for logging. */
  private static final class EmptyServiceManagerWarning extends Throwable {}

   */
  private static final class NoOpService extends AbstractService {
    @Override
    protected void doStart() {
      notifyStarted();
    }

    @Override
    protected void doStop() {
      notifyStopped();
    }
  }

  /** This is never thrown but only used for logging. */
  private static final class EmptyServiceManagerWarning extends Throwable {}