Mike Gerasymenko, Staff iOS Engineer at Delivery Hero, delivered an engaging 15-minute session on making apps modular and testing only what's changed during this year's Mobile DevOps Summit 2023. He emphasized the importance of modularization in large-scale app development, highlighting its benefits in terms of scalability, team collaboration, and efficiency. Gerasymenko discussed various tools and techniques for implementing modular architecture, including Swift Package Manager, which enables teams to manage dependencies and speed up PR checks and CI processes. He also introduced an open-source tool called XcodeSelectiveTesting, allowing developers to run tests only relevant to the changes made in their codebase. By adopting a modular approach, developers can significantly reduce testing time and ensure that they're only testing what's changed, making it easier to maintain and update large apps.