The documents are tough, but people do pass them. I did, and plenty of people have been hired since me. I don't have a background as an editor. The thing is, in order to pass this test you're going to need three things: 1. Excellent written English and grammar, 2. Some knowledge of (and patience for) ESL learners and the mistakes they make, and 3. An understanding of scientific reports and basic statistics. Reading through the complaints here, I suspect the reason 'professional editors' and 'English master's degree holders' and such aren't getting through is a lack of science background. A lot of the work we edit is academic and scientific, and without a basic knowledge of that (I only have a bachelor's in psych, so my knowledge is pretty basic), you can't really do a lot of the work that comes in, and it's probably not worth you doing the test and then getting angry on Glassdoor.
All questions were really short as she didn't really care much about what was being said as only out to create a "bank" of people she could call on when busy by pretending to put interviewee's on "trial.