When practising with the Cambridge IELTS books, try this study technique:
1. Choose a reading passage.
2. Go to the back of the book and get the correct answers.
3. Study the passage with the aim of proving why those answers are correct.
4. Make a keyword table.
When you know what the answers are, you can focus on exam technique: searching for keywords, then reading the relevant part of the passage carefully. You might find this helps you more than simply testing yourself would.