One of the absolute most challenging tasks in developing with an Event Driven Architecture is trying to automate testing through all your asynchronous system behavior. It's challenging sometimes to know when your test can move from "Act" to "Assert" when there's asynchronous behavior and messages firing. It's sometimes even more challenging to understand what's happening inside your system when tests inevitably fail sometimes.

In this talk I'll share the tooling, lessons, and strategies we've used in the "Critter Stack" community for testing effectively against asynchronous messaging and processing, controlling database state for reliable tests, predictably checking expected state even with asynchronous event projections and subscriptions, and all the things we've tried to build into our tools to help create visibility into just what's happening in test harnesses when messages and events are flying around your system.