To be honest, there aren't any free ASVAB practice tests available online that are great resources. Some are very different from the actual ASVAB, but even the better ones are often shorter than the actual test and may have simpler questions than what you see on test day.
You can still use it, but we recommend using it only as a supplement, not as a primary research resource, and only using it after you've taken at least two official pre-test to find out what the ASVAB is. for example. Here are some better tests for ASVAB practice:
4 Test: This practice test approximates the ASVAB in difficulty, but it is not time consuming and the explanation of the answers is rather short.
ASVAB Practice Test: This practice test is time consuming and exhaustive, and the questions match the ASVAB (although some are easier). However, it breaks the flow of the test by telling you whether you received a correct or incorrect question right after the answer.
Preparation for the Union exam: This skill test is time-consuming and incomplete. It also tells you whether you received a right or wrong question after you answered it. However, the question is worth it, as is the explanation of the answer.
Online ASVAB Practice Test: This practice test is complete, but the questions are much simpler than what you see in the actual ASVAB and there is no explanation for the answers.