Many students prepare for the IELTS exam by doing lots of practice tests. But too much testing is a bad idea.
I think that there is a difference between 'testing' and 'training'.
- shows you what your current level is
- gets you used to working in exam conditions (e.g. with a time limit)
- means that you focus on vocabulary for a particular topic
- or work on particular grammar mistakes
- or work on a technique for a particular part of the exam
A good example of training is when you practise writing introductions. Sometimes I spend a whole lesson with my students just doing different introductions. We practise one technique until students become good at it.
So, how much 'training' and how much 'testing' should you do? Well, a good idea might be to spend Monday to Friday training, preparing and working on language. Then test yourself at the weekend - if you've worked hard, you might see an improvement!