I don't remember exactly what the sample was about, but I'd expect a social work related topic (to clarify, I was more surprised by the length of the article, but it was certainly doable!). The interviewer gave us some context and instructions on exactly what they wanted us to do in the sample, which was really helpful. And don't worry, you don't have to talk about the article in the interview, it's just a written exercise you do on your own Good luck, I'm sure you'll do great!