Supplier<Integer> memoizedSupplier = Suppliers.memoize(countingSupplier);
    checkMemoize(countingSupplier, memoizedSupplier);
  }

  public void testMemoize_redudantly() {
    memoize_redudantlyTest(new CountingSupplier());
    memoize_redudantlyTest(new SerializableCountingSupplier());
  }

  private void memoize_redudantlyTest(CountingSupplier countingSupplier) {

    Supplier<Integer> memoizedSupplier = Suppliers.memoize(countingSupplier);
    checkMemoize(countingSupplier, memoizedSupplier);
  }

  public void testMemoize_redudantly() {
    memoize_redudantlyTest(new CountingSupplier());
    memoize_redudantlyTest(new SerializableCountingSupplier());
  }

  private void memoize_redudantlyTest(CountingSupplier countingSupplier) {

   * delegating calls until it returns valid data.
   *
   * <p>If {@code delegate} is an instance created by an earlier call to {@code memoize}, it is
   * returned directly.
   */
  public static <T extends @Nullable Object> Supplier<T> memoize(Supplier<T> delegate) {
    if (delegate instanceof NonSerializableMemoizingSupplier
        || delegate instanceof MemoizingSupplier) {
      return delegate;
    }

   * delegating calls until it returns valid data.
   *
   * <p>If {@code delegate} is an instance created by an earlier call to {@code memoize}, it is
   * returned directly.
   */
  public static <T extends @Nullable Object> Supplier<T> memoize(Supplier<T> delegate) {
    if (delegate instanceof NonSerializableMemoizingSupplier
        || delegate instanceof MemoizingSupplier) {
      return delegate;
    }

 * memorized and kept as long as supplier instance is kept open.
 * <p>
 * This class is not thread safe and must be used from one thread only, while the constructed {@link RepositorySystem}
 * is thread safe.
 * <p>
 * Important: Given the instance of supplier memorizes the supplier {@link RepositorySystem} instance it supplies,

        break;
      case TERMINATED:
      case FAILED:
        throw new AssertionError();
    }
  }

  private void enqueueFailedEvent(final State from, final Throwable cause) {
    // can't memoize this one due to the exception
    listeners.enqueue(
        new ListenerCallQueue.Event<Listener>() {
          @Override
          public void call(Listener listener) {
            listener.failed(from, cause);