Explore key coding and architecture lessons for building safe, testable Scala production systems in this conference talk from Scala Days Chicago 2017. Discover how x.ai leveraged Scala to create an advanced meeting scheduling application, focusing on important coding and testing patterns, open-source libraries, and the transition to a functional "I/O vs. pure" architecture. Learn how to improve application testability at multiple levels and gain valuable insights on evolving your own application architecture. Benefit from the speakers' experience in building real-world production applications that are easy to test and safe for developers of varying Scala expertise to work on.