GMAT Club Tests offer hard Quant CAT tests and a smaller number of verbal tests (over 1,100 quant questions and 388 verbal questions). The questions are generally above average difficulty though some easier ones have been introduced as well. You can see the exact distribution of questions here. To learn about the scoring algorithm precision, please see this discussion. Finally, GMAT Club tests require a subscription but 10 days a year, we offer them for free on US public holidays.