<ul data-eligibleForWebStory="true"><li>Event sourcing revolutionizes testing by replaying real history instead of faking state.</li><li>Traditional testing focuses on CRUD operations using fixtures, while event-sourced testing tests business rules without a database.</li><li>Unit tests for commands and aggregates test decisions, not side effects, ensuring business rules are followed.</li><li>Integration tests for event handlers verify projections and side effects, like user upgrades based on deposits.</li><li>End-to-end tests replay real scenarios from production data to test entire workflows.</li><li>Tools like RailsEventStore, Eventide, and Cucumber make event-based testing easier.</li><li>Avoid event-sourced testing for simple CRUD operations or legacy systems without event-sourcing.</li><li>For transitioning to event-based testing, start small, add event publishing to critical features, and gradually migrate as you refactor.</li></ul>

Testing Event-Sourced Systems: No More Fixtures, Just Replays

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