Move return statement

- Allows debug statement to run, ever
- Should return a response object if no exception is raised, this seems correct
Add in new libs for testing

- for when you run `nosetests` rather than relying on setup tools
- imports https://github.com/dropbox/responses which seems like a good way to test the responses module we're using
Add response assertion to `get_data_set_by_name` test

- Tests that we actually get a response
- Not sure whether we should be debug printing as well, but whatever
- Uses responses to make assertions about the way the request and the response objects look