implement automated tests

[lanterndev]

Set up comprehensive tests that cover all the edge cases, app engine limits, exercise all branches of the code, etc.

[lanterndev]

urlfetch call passes validate_certificate=True. Test what happens if the upstream server certificate is invalid. https://developers.google.com/appengine/docs/python/urlfetch/fetchfunction does not say.

[lanterndev]

mucho progress in 8b81439