If possible, most tutors recommend beginning your preparation around 6 months before the official test, to leave time for learning new concepts if needed. But if you don't have that much time, it's good to take at least a couple of practice tests so there aren't any surprises on test day.
For ISEE preparation, check out: https://iseepracticetest.com
For SSAT preparation, check out: https://ssatpracticetest.com
For ACT preparation, check out: https://testinnovators.com/act/
For SAT preparation, check out: https://testinnovators.com/sat/
For PSAT preparation, check out: https://testinnovators.com/psat/
For HSPT preparation, check out: https://testinnovators.com/hspt/