Add Tests, Assert, and Logging to QuizManager.

[Lucky-Yuan00]

This issue covers the addition of unit tests, defensive programming through assert statements, and logging functionalities in the QuizManager class. The goal is to ensure code reliability and traceability.

The tasks include: Writing tests to validate the functionality of adding and removing topics. Implementing assert statements to check for null or invalid inputs. Adding logging to track important operations like starting a quiz and saving results.

[Lucky-Yuan00]

This issue has been completed. I have added unit tests for the QuizManager, including assert statements to validate input, and implemented logging to track key operations such as starting quizzes and saving results. All tests have been run successfully. Please review and merge the changes.