Move doctests from utils.py

• Moves date conversion functions to separate test_utils.py
• Adds a couple of missing exceptions for these
• Also, adds tests for API functions with mock_requests

utils.py at 100% in coverage - yay!

Closes #27 (closed)

changed milestone to %DevOps Sprint 112

changed the description

approved this merge request

I love that GitLab's code coverage shows me that the tests are actually being run :).

mentioned in commit 5de9d8f3

merged