Update mock import to work with Python 3.13

[davispuh]

Description

There's no mock import in Python 3.13 so need to update to unittest

Types of change

Update mock import to unittest.mock

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.