Test run failures

[sjmf]

Tests are run using python -m pytest. However, several of the unit tests are failing at the moment due to difficulty patching the modules they use.

Most tests run correctly when running the single file, e.g. python -m pytest tests/backend/test_keyboard.py. However, due to patching requirements for the modules serial, pynput and tkinter (these being the 3 giving the most trouble), the tests can fail when run as a suite in concert.

PyTest's behaviour is that once a module has been loaded, it can no longer be patched. This leads to a situation where tests following can receive different system state dependent on what ran previously.

Test run report to follow.

[sjmf]

Furthermore, pynput and tkinter modules cause test failures on GitHub Actions due to the headless environment. These need to be fully patched when testing, but because of the aforementioned difficulties in applying patches (especially after modules are inadvertently loaded) tests which run successfully locally can fail when running under Actions.