Review how coverage is achieved

[tansaku]

We should review the full process of achieving coverage in this assignment. #27 highlighted a potential shortcoming in the instructions.

I've been concerned for a long time that students are being asked to wrap a lot of code (that they didn't write) in tests. That's great as a legacy activity, but it's not labelled as such, and is potentially confusing in an assignment that's supposed to be about the acceptance unit test cycle - I'd be more comfortable if the tests for all existing functionality were in place and the students were focused on ensuring coverage for the code they were writing themselves?