A hands-on guide to building and testing event-driven projections using Emmett, Pongo, and PostgreSQL in Node.js. Covers defining event types for a shopping cart domain, creating single-stream projections that materialize read models into PostgreSQL JSONB collections, and registering them as inline projections (transactional with event appends). Also demonstrates a BDD-style testing approach using PostgreSQL TestContainers, with Given/When/Then helpers to verify read model creation, updates, and deletion when events like ShoppingCartConfirmed return null from the evolve function.
