After a decade of developing customer mobile apps, I switched to working on developer tooling. Over the past year, my team at Adyen has been developing an end-to-end testing framework to test payment terminals and mobile payment SDKs. Over the course of this development, we’ve had to work with Kotlin Symbol Processing(KSP), Kotlin Compiler Plugins, custom JUnit runners, IntelliJ IDEA plugins, and a lot more. Although we hear a lot about these frameworks, it’s often difficult to understand the context in which they should be used. In this talk, I will walk you through our journey of experimenting with these technologies, how they fit into the puzzle, practical examples, and the overall thought processes behind developing such a custom end-to-end testing framework.