def METHOD_NAME(source: UPDATABLE_DATA, key: str, action: str, to_set: Any, result: UPDATABLE_DATA) -> None:
    """Test _deep_get behaves as expected."""
    cpy = copy.deepcopy(source)
    killswitch._deep_apply(target=cpy, path=key, to_set=to_set, delete=action == 'delete')
    assert cpy == result