During December 2024, Kien Nguyen focused on enhancing authentication reliability for the taquocy/e-commerce-for-testing repository by developing targeted unit tests for the Sign In component. Using JavaScript and React, Kien applied test-driven development principles to cover scenarios involving valid credentials, incorrect passwords, and non-existent emails. This work validated user feedback mechanisms and ensured correct user experience messaging, laying a stronger foundation for future quality assurance automation. The approach emphasized code quality and traceability, linking changes directly to specific commits. While the scope was limited to a single feature, the depth of testing improved test coverage and reduced the risk of regression.