EqualsTester tester =
        new EqualsTester(
            /* itemReporter= */ item -> {
              List<Object> factoryArgs = argGroups.get(item.groupNumber).get(item.itemNumber);
              return factory.getName()
                  + "("
                  + Joiner.on(", ").useForNull("null").join(factoryArgs)
                  + ")";
            });