Should You Do Free Work at a Job Interview?
If you're currently searching for a new job, you may encounter something you haven't run into before: Employers are increasingly asking job candidates to do work projects and exercises as part of the hiring process.
These exercises aren't the typing tests and software assessments of the past; rather, more and more often, they're mini-projects designed to see your work in action so that the employer can get a firsthand look at how you approach work challenges. For example, if you're applying for a communications position, you might be asked to write a press release or create a mock publicity plan for an event. Or if you're applying for a research analyst job, you might be asked to write a memo on the ramifications of a particular piece of legislation.
Source: http://money.usnews.com/money/blogs/outside-voices-careers/articles/2017-04-10/should-you-do-free-work-at-a-job-interview