Learning express has practice tests and supplemental materials, such as ebooks, for you to use while you prepare for your exam. To access the material, create an account (it's free). It will keep track of where you left off and which tests you've done.
Once you are in Learning Express, go to the Career Preparation center. Then go to Prepare for an Occupation Exam section, and scroll down to Commercial Drivers' License (CDL).
Or click the link below to go directly to the practice exam in Learning Express.