What problem does it solve? When building applications with Domain-Driven Design, starting from infrastructure or UI concerns often distorts the domain model, leaks technical concerns into business logic, and makes testing difficult. This Skill provides a disciplined development procedure that keeps the domain model pure and testable. ## Core Features & Use Cases - Test-First Domain Modeling: Define domain model behavior as tests first, then implement value objects, entities, and aggregates to satisfy them. - Ordered Development Workflow: Build in the sequence of domain model, in-memory repository, use cases, then infrastructure and interface adapters. - In-Memory Repository Pattern: Implement repository interfaces backed by in-memory collections so use cases can be tested without a database. - Use Case: When starting a new feature like task management, write tests for the Task aggregate's behavior first, create an in-memory TaskRepository, implement CompleteTaskUseCase against it, and only then connect the real database and controllers. ## Quick Start Ask the AI to design and implement a new feature using test-first domain modeling with an in-memory repository before adding infrastructure.
