Worked on the neos/neos-ui repository to deliver UI constraints support through the GetTreeQuery feature, focusing on improving validation reliability and user-facing behavior. Utilized PHP and behavior-driven development practices to adjust test fixtures, ensuring error messages and CSS classes matched expected outputs. This approach stabilized UI tests by reducing flaky failures and enabled more accurate validation flows for constraints handling. By aligning error messaging with user experience expectations, the work contributed to lower support overhead and enhanced perceived quality. All changes were tracked and documented in a focused patch, demonstrating a methodical approach to testing and feature delivery within the project.