This website is useful if you want general grammar test practice online:
A few more free online tests:
Written comprehension: http://www.englishclub.com/esl-exams/levels-test-wc.htm
Cambridge level test: http://www.cambridgeesol.org/testyourenglish/
A few mock IELTS tests: http://learnenglish.britishcouncil.org/en/ielts
There are also lots of books available from the Study Centre. I suggest you ask the teacher in there what they can recommend; the stock of books is increasing all the time.
If you know which aspect of grammar you need to revise and practice, you could use: