I think the reader role should not always be kept, this should depend on the delegate roles.
I'd propose to rename the test and add an explicit `change_permission` for making it clear that the reader role cannot be delegated (although this might already be the case but is too implicit):

```python
       self.folder.manage_permission(
            'Sharing page: Delegate Reader role',
            roles=[],
           acquire=False)
```