Fix the BubbleSorter and add the unit test.

[yanxiaodi]

Description

135

Checklist

• [x] An issue was first created before opening this pull request
• [ ] The new code follows the contribution guidelines
• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests to ensure that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes

[aalhour]

Thanks for your contribution @yanxiaodi.