Add stubs for the error handling tests.
Set up the first error handling test, currently failing.
Fix the test for the error handling.
Correct issues with the test suite.

Previously, various Expecta calls were not using the correct methods
(beNil instead of beNil()). This will cause some tests to report false
positives.
Add Rick Harrison's error handling method for testing.
Enhance the behaviour of the response serializer.
Cover the not found error.
DRY up the error spec.
Consolidate all of the successful response specs.
Improve error handling when given certain errors.
Test the rate limiting error response.