In addition to the interview you may be asked to do other tests to demonstrate your ability to do the job.
Whether you are required to do so will depend on the nature of the position and the preferences of the selection panel.
Usually you will be informed when the panel contact you to arrange an interview. However, if you're in doubt, check with the selection panel.
Types of tests will vary greatly depending on the job, but may include:
If you are asked to do a test, try to find out as much as you can about it beforehand and prepare in any way you can. For example, if you are going to given a typing speed test, practice at getting your speed up beforehand.