Write unit tests for the above selected code, following each of these instructions:
- Use `vitest` please, not jest
- Properly set up and tear down
- Add uppercase for the first letter of the first word for each it
- Include important edge cases, try to reach a full coverage
- The tests should be complete and sophisticated
- Give the tests just as chat output, don't edit any file
- Don't explain how to set up `vitest`