STARTER_CHARACTER = 🔴🟢

Outside-In TDD with Hexagonal Architecture

Build features by driving design from the outside in. Every feature starts with a failing acceptance test. Design emerges through disciplined Red-Green-Refactor cycles. Infrastructure is deferred until the domain API is proven.

Unlike inside-out TDD with mocks, this approach tests behavior at the boundary — not implementation details — making the suite refactor-friendly by design. See methodology.md.

For canonical terms used throughout, see references/glossary.md.

The Two Loops

Outer loop (Acceptance test): Write a failing test scoped at the service/system boundary. This test exercises integration across Bounded Contexts using in-memory adapters. It defines "done."

Inner loop (Red-Green-Refactor): Cycles inside a Bounded Context to make the outer test pass. Drop into this loop only to implement what the acceptance test demands.

Every feature starts from the outside in. The acceptance test drives the process.