Refactor unit tests

PR to refactor the test suite improving our coding practices and code style to organize the tests into classes with functions.

I'd meant to do this for a while and only just got around to it. This PR just breaks up the unit tests so that they are easier to debug in the event of a test failure by making each test function test a single call of the function in question.

The tests are also grouped logically into test classes where each class contains tests for a single function in hyswap.

No hyswap functionality is changed or altered in this PR, it is purely to improve the test suite.