Uber successfully migrated one million lines of JUnit tests in just two weeks, a significant feat that highlights the efficiency of their process. The migration involved transitioning from JUnit 4 to JUnit 5, which is part of their broader effort to modernize their codebase. Uber faced challenges typical of large-scale code migrations, such as maintaining test coverage and ensuring compatibility with existing systems. They utilized automated tools and strategies that minimized manual intervention, which helped accelerate the timeline. During the migration, Uber emphasized the importance of maintaining a robust testing framework. They implemented a systematic approach to identify and resolve issues quickly, which was critical given the scale of the project. The use of automation not only sped up the process but also reduced the likelihood of human error, ensuring that the migration did not compromise the integrity of their testing suite. The success of this migration is a testament to the effectiveness of combining modern tools with strategic planning. Uber's experience can provide valuable insights for other organizations looking to undertake similar migrations, particularly in terms of resource allocation and the importance of automated solutions. Their approach serves as a case study for balancing speed and quality in software development.