To test pysandbox, simply create a test file, then try to delete it, or overwrite it.
@omz is no longer supporting pythonista2, I doubt you will get a new option. (And since no one uses pythonista2 anymore, it wouldn't make much sense to to add those features to pythonista3). Plus, your whole premise is flawed to begin with ... If you have anything worth saving, you should be backing up.
I will point out a middle ground which is this:. If you place unsafe files in the private folder, and del os.path.expanduser, and pathlib.Path.home, and sanitize sys.path, then you should be able to run untrusted code, since those files have no way of knowing how to find the shared folder. iOS prevents them from doing listdir in the parent of the app folder or group folder, so it is impossible for another app to find the files to delete (unless it is a script specifically targeting YOU. But if you are worried about that, you shouldn't ever take your iPad out of it's tin foil package to begin with)