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)
                    + ")";
              }