What/How to test

https://www.youtube.com/watch?v=dJUVNFxrK_4	The single most influential reference in this list. Must-Watch
https://www.toptal.com/qa/how-to-write-testable-code-and-why-it-matters	explains good and bad code structure, testability
https://stackoverflow.com/questions/1595952/how-to-write-tests-without-so-many-mocks	Read last comment - test highest level that does not require mocks. Influenced my decision to reorganize my code into more single-purpose classes, with public functions exposing their behaviours.
https://www.youtube.com/watch?v=EZ05e7EMOLM	Test Behaviours, Not Classes/Methods/Functions. Tests (not code) should should not interfere with each other, or produce side-effects that might break another test.
https://zeroturnaround.com/rebellabs/the-correct-way-to-use-integration-tests-in-your-build-process/	What are integrations tests, how/when to use them
http://istqbexamcertification.com/python-unittest-framework-tutorial-examples/
http://docs.python-guide.org/en/latest/writing/tests/
http://pythontesting.net/framework/pytest/pytest-introduction/

What NOT to test