which GMAT tests are good

There is always gmatclub tests, which are free for our active members.
https://gmatclub.com/wiki/Tests

I found Kaplan to be the hardest and most helpful for studying. However, the best tests to give you an idea of where you stand in terms of final GMAT Score are the PowerPrep tests - don't just waste them. Save 1 for the last week before the test to get an idea about your performance. Mine was close.

Also, would recommend to focus more on basics and foundation of your knowledge. Some people prefer to study using tests - that's a hit and miss tactics that works, but not as efficiently as the thorough understanding of concepts for math or verbal. In my mind it is a waste of tests if you don't have a good understanding/knowledge about the topics covered.

Just my 2 cents. What do i know...