UI tests have supported re-engineering of the Cookpad iOS app, which has over 35 million users. The app is developed continuously, releasing every 2-4 weeks. UI tests were implemented in 2014 to check external and internal changes as the app is re-written and refactored. Automated UI tests help reduce fear for developers during re-engineering. They also help ensure quality and stability as the mobile environment and services change frequently. UI tests are important for legacy re-engineering projects to enable continuous development.