For official practice tests made by the maker of the GMAT, go to MBA.com. Those tests are the practice tests that are most like actual test. The first two are offered free. There are four more that you can purchase in two sets of two tests.
Some people stick with using official tests only, while others use a variety of tests, and I have seen one person take around 25 different practice tests in preparing for the GMAT.
One thing to be aware of is that while resetting and retaking official, or other tests, can be useful in certain ways, the experience of taking a retaken test is not quite the same as that of taking a fresh test or the actual GMAT. So be careful not to count too much on retaken tests during your preparation.
Last edited by MartyMurray on Wed Feb 06, 2019 9:12 am, edited 1 time in total.