ImmutableList<T> group = groups.get(groupNumber);
      for (int itemNumber = 0; itemNumber < group.size(); itemNumber++) {
        // check related items in same group
        for (int relatedItemNumber = 0; relatedItemNumber < group.size(); relatedItemNumber++) {
          if (itemNumber != relatedItemNumber) {
            assertRelated(groupNumber, itemNumber, relatedItemNumber);
          }
        }

        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)
                    + ")";
              }
            });