The Language Project is a school based in Bristol in the UK. Their website has over 150 pages of free multiple-choice practice exercises at three levels. Unfortunately, if you get an answer wrong, the correct answer is not shown and you get no feedback to help you understand why your answer is (in)correct. You have to keep trying till you get the answer right and even then you won't know why. So for students these exercises are not very useful but teachers could find them useful for testing purposes, especially as they can be printed out.