Adding tests for resolve_deps.py

We should also refactor the code so that we don’t have to use the responses module so heavily - we should separate into two classes the getting info from github and then processing that info
Test case for get_reqs_recursive of a looping formula

Also fix a bug where calling get_reqs_recursive twice in the same interpreter would re-use the same python dict object to store dependancies in. This wouldn’t affect actual use of the command line script but is a bug none the less.
Don’t use a large literal string - json-ify a python object instead
Use `expected, actual` param order for all test assertions.
Get env var when we need it, not at module import time.

This way we don’t have to set an env variable before importing `resolve_deps` in the tests which needed a comment to explain why it was there.