tdd

name	tdd
description	Test-first variant of implement: understand the desired behavior, write a failing test, make it pass, then simplify.
user-invocable	true
argument-hint	<task reference or behavior> e.g. 'LIN-123' or 'retry logic for API client'

Test-Driven Development

Use for behavioral changes where a failing test can define the desired outcome before implementation.

Workflow

1. Understand

• Read the request, task, issue tracker item, plan, spec, and relevant code as available.
• Identify the desired behavior, existing contracts, failure paths, and verification.
• If a spec exists, note its invariants, decisions, and testing strategy.
• Ask before writing tests when missing information would materially change behavior, scope, safety, contracts, data shape, or verification.

2. Red

• Write the smallest failing test that proves the desired behavior or reproduces the bug.
• Run it and confirm it fails for the expected reason.

3. Green

• Write the minimum implementation needed to pass the test.
• Preserve existing contracts unless the task explicitly changes them.
• Add failure-path tests where they matter.

4. Refine

• Simplify code and tests while they stay green.
• Run the focused checks first, then the project's wider checks, before finishing.
• Report the failing-then-passing test and final verification.

Rules

• Do not write implementation code before a failing test for the behavior.
• If an assumption is low-risk, make it explicit and keep moving.
• Tests describe behavior, not implementation details.
• Prefer real boundaries over mocks when practical.
• Skip TDD for documentation, formatting, or non-behavioral scaffolding work.