The Enveritas Group (external link) website makes it easy to apply for freelance writing, editing, and translation work. You simply enter your biographical information and include two short writing samples. There may be a written test later but among the freelance sites I’ve written about at this site (internal link), their application process is easy and straightforward.
Update: January 5, 2016. The group got back to me and indeed there is a creative writing test and a short editing test to take. Took about forty-five minutes. I’ll let you know how I fared.