As someone who has already done and passed the test, the mock test that I found that was the most helpful and the closest in nature to the actual test, was
http://www.yourlibrary.ca/citizenship/
Please remember that the actual test is there to test your basic knowledge and understanding of Canada, its history, laws, and culture. That's all. There are no trick questions. In most cases, if you've done the reading, the answers will be obvious.
Keep calm, and good luck.
