Not sure about what kind of exam you refer to. If it's for general recruitment, it is a three-hour mutiple choice exam. There will be five or six essays to read, and all questions will be about the writing style, word choosing, as well as locating misrepresentation. It is not particularly difficult, but need you to read fast. However, completing this exam is far from getting a job.
If you refer to some writing exam for a specific position, I don't have experience, but my guess would be either mutiple choice questions or an essay on a given topic. It is definitely closer to a job!
Good luck!