Worked on stabilizing the UI test surface for the jupyterlab/jupyterlab repository, focusing on improving the reliability of toolbar popup interactions. Addressed a race condition by introducing an asynchronous assertion that waits for the resizer to complete before opening the popup, ensuring more deterministic test outcomes. This approach reduced flaky tests and contributed to smoother continuous integration workflows. Leveraged TypeScript for front end development and testing, codifying a robust synchronization pattern for UI tests that will support future dynamic toolbar changes. The work emphasized test determinism and reliability, laying a foundation for more predictable releases and a better developer experience.