- Add patched rootdir fixture to all config tests. I think this isn't strictly necessary but it does ensure that any config tests that need to write files don't accidentally write to user data locations.
- Be more careful when calling `get_config()` in the tests, by clearing the LRU cache before and after. This ensures a test doesn't reference the singleton config created by a previously run test.
- Add test for env var parsing.
- Add test for config writing in the context of `get_config()`. This is effectively a mini e2e test for the config lifecycle.