docs: public static void assertStatesMatch(Iterator<?> left, String leftName,
        Iterator<?> right, String rightName, String itemTypePlural) {
      if (left.hasNext() != right.hasNext()) {
        if (left.hasNext()) {
          throw new IllegalStateException(
              leftName + " has more " + itemTypePlural + " than " + rightName);
        } else {
          throw new IllegalStateException(
              rightName + " has more " + itemTypePlural + " than " + leftName);
        }
      }
    }