Fastly has introduced local Fanout testing for its Compute platform, enabling developers to build and test real-time services like Server-Sent Events, HTTP streaming, and WebSockets-over-HTTP without deploying to a live Fastly service. Previously, testing these features required a full deployment, but updates to the Fastly CLI and the Viceroy local testing server now allow developers to test Fanout functionality entirely on their local machines. This is facilitated by Pushpin, an open-source proxy server project that acts as a real-time message broker, maintaining long-lived connections and delivering messages as directed by the backend. The new local testing capability streamlines the development process by allowing for full end-to-end testing of Fanout features within a local environment, which includes setting up a local architecture with Viceroy and Pushpin for comprehensive simulation of production scenarios. Developers can now iterate and validate real-time behavior locally, enhancing the flexibility and efficiency of building with Fastly's event-driven architecture.