}

  private Item<T> getItem(int groupNumber, int itemNumber) {
    return new Item<>(groups.get(groupNumber).get(itemNumber), groupNumber, itemNumber);
  }

  static final class Item<T> {
    final T value;
    final int groupNumber;
    final int itemNumber;

    Item(T value, int groupNumber, int itemNumber) {
      this.value = value;
      this.groupNumber = groupNumber;
      this.itemNumber = itemNumber;

    EqualsTester tester =
        new EqualsTester(
            new ItemReporter() {
              @Override
              String reportItem(Item<?> item) {
                List<Object> factoryArgs = argGroups.get(item.groupNumber).get(item.itemNumber);
                return factory.getName()
                    + "("
                    + Joiner.on(", ").useForNull("null").join(factoryArgs)
                    + ")";
              }