mgr/dashboard: Refactor Python unittests and controller
Pull request ID:
- Make use of the KVStoreMockMixin class to get rid off duplicate code.
- Fake the index.html file to be able to run tests/test_home.py locally without building the frontend in production mode.
- Encapsulate helper functions in controllers/home.py, otherwise tests/test_feature_toggles.py need to fake the filesystem because load_controllers() will load the home.py controller and fail due missing files in the filesystem.
This issue is opened retrospectively to be able to backport it to Nautilus using the usual backport workflow.