Depending on what you're preparing for, you may want to check out the (FREE!) flash cards on our self-study page: https://www.isc2.org/Training/Self-Study-Resources
There are self tests, with answers and explanations, at the end of each CBK in the official ISC2 textbook for each exam. Similarly if you buy an all in one guide, you get self test questions and answers. It may be wise to study the material before using the self tests. It could be quite demotivating to score poorly on the tests if you haven't studied the materials. Alternatively, it may give you a false sense of security (no pun intended). There simply isn't a substitute for learning the material.