tsddlisted

# Test-Spec Driven Development (TSDD) ## Scope This skill governs the **methodology layer** of day-to-day coding work — how requirements, design decisions, and implementation are recorded and evolved, and in what order work proceeds. It is deliberately language-agnostic. TSDD means the test suite is the durable specification. TDD is the operating discipline used to grow that specification one executable example at a time. Out of scope and delegated elsewhere: - Language-specific conventions (mock libraries, fixture patterns, lint rules, assertion style, package manager commands, module layout) → the relevant `*-style` skill and `rules/coding_guideline.md`. - Project and CI bootstrap (flake, direnv, language init, CI workflow scaffolding) → the relevant `*-init` skill. - ADR selection, repository inspection, layout, status, supersession, templates, and workflow → the `adr` skill. If a rule below starts feeling like a language-specific implementation detail, it belongs in one of those skills, not here. ## Core Principle **The spec is the test suite. Prose documents carry only Why.** Natural-language specification documents become a second source of truth that drifts from the code, violates DRY, and doubles the cost of every requirement change. Under this methodology, requirements live inside executable tests, implementation is self-documenting via code and types, and the only human-written prose captures _why_ a decision was made — which code cannot express anyway, so