How GitHub reduced testing time for iOS apps with new runner features

GitHub has utilized Apple Silicon and macOS runners for GitHub Actions to streamline and quicken the development process for their iOS app. They shifted from using one workflow for the entire codebase to splitting their test suite into separate modules for each job, using M1 macOS runners to build and test independently. This resulted in a significant decrease in testing time, from 38 to 15 minutes, improved efficiency, and allowed for quicker feedback on pull requests. The company was also able to improve reliability and build performance, with increased compatibility with the latest iOS, iPadOS, watchOS, and tvOS versions. This change has allowed the GitHub iOS team to leverage the power of concurrent runners which initiate 50 jobs for each pull request, allowing for efficient modular testing in parallel.