Tdd Typescript

TypeScript TDD Adapter

This skill adapts the shared TDD workflow for framework-neutral TypeScript.

Load First

Use the shared TDD skill as the source of truth:

• Read ../tdd/SKILL.md for the red-green-refactor workflow, horizontal-slice warning, planning checklist, tracer bullet loop, and cycle checklist.
• Read ../tdd/tests.md when choosing test shape or reviewing whether a test verifies behavior.
• Read ../tdd/mocking.md when deciding whether to mock, fake, or use real collaborators.
• Read ../tdd/interface-design.md when changing an exported API or dependency boundary.
• Read ../tdd/deep-modules.md and ../tdd/refactoring.md before refactoring after GREEN.

Do not duplicate the shared workflow in your reasoning or output. Apply it, then add the TypeScript-specific decisions below.

Use This For

• TypeScript libraries and package APIs.
• Node services, application modules, and handlers.
• Exported functions, classes, hooks-free services, or public module contracts.
• Existing Jest, Vitest, Bun test, Node test runner, or repository-specific TypeScript test setups.

Use tdd-nextjs-jest instead when React rendering, Next.js App Router behavior, server actions, route handlers in a Next runtime, or Testing Library DOM behavior are part of the public contract.

Public Test Surface

Choose the narrowest public TypeScript surface that proves the behavior:

• Exported function or value object.
• Public class or service method.
• Package entrypoint.
• Application use case or command/query handler.
• HTTP or message handler when that handler is the module's public boundary.

Avoid testing private helpers, internal module wiring, constructor calls, call order, or file layout. A refactor that preserves exported behavior should not break the test.

TypeScript Boundaries

Keep internal project modules real. Mock or fake only true system boundaries:

• External APIs, SDKs, databases, queues, network, file system, environment, child processes.
• Time and randomness.
• Expensive process boundaries that are not the behavior under test.

Prefer small typed fakes or explicit dependency objects over broad jest.mock, vi.mock, or module-level mocks. Specific boundary methods such as getUser or createOrder are easier to fake than generic request methods that require conditionals in test setup.

Red-Green Commands

Use the repository's existing runner and focused filters:

npm test -- checkout
pnpm test checkout
bun test checkout
vitest checkout

After focused GREEN and refactor steps, run the relevant broader TypeScript suite before closing.

End Report

Include a concise "Tests implemented" list:

• Behavior or test name.
• Scope: unit, integration, api/handler, or repository-native equivalent.
• File path.
• Focused and broader test commands run, including unrelated remaining failures.