**Is your feature request related to a problem? Please describe.** There are currently no automated tests for `user.py`, making it difficult to ensure that the `User` class and its methods work as intended and to catch regressions during development. **Describe 1~3 use cases of the purposed feature** - Verify that the `User` class can correctly add, update, and remove articles and revisions, and that user contributions are accurately tracked and filtered. - Ensure that methods for fetching, saving, and backfilling contributions from both the wiki API and the database behave as expected, including handling edge cases like deleted or moved revisions. - Confirm that result formatting, statistics counting, and analysis methods produce the correct output for various user activity scenarios. **Describe alternatives you've considered** - Relying on manual testing or indirect coverage through higher-level tests, but this does not guarantee that all code paths in `user.py` are exercised. - Adding only integration tests, which may not catch issues specific to the user logic and its interactions with articles, revisions, and contributions. **Additional context** Unit tests for `user.py` will help maintain code quality and reliability. Tests could be implemented using pytest or unittest, and should cover both typical and edge-case usage of the `User` class and its methods.