Agent-Skills.md

Agent Skills: Test-Driven Development (TDD) Standard

Enforces Test-Driven Development (Red-Green-Refactor). Use when writing unit tests, implementing TDD, or improving test coverage for any feature. (triggers: **/*.test.ts, **/*.spec.ts, **/*_test.go, **/*Test.java, **/*_test.dart, **/*_spec.rb, tdd, unit test, write test, red green refactor, failing test, test coverage)

UncategorizedID: hoangnguyen0403/agent-skills-standard/common-tdd

Repository

hoangnguyen0403/agent-skills-standard
HoangNguyen0403License: Apache-2.0
362103

Install this agent skill to your local

pnpm dlx add-skill https://github.com/HoangNguyen0403/agent-skills-standard/tree/HEAD/.agents/skills/common/common-tdd

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.agents/skills/common/common-tdd/SKILL.md

Skill Metadata

Name
common-tdd
Description
'Implements a strict Red-Green-Refactor loop to ensure zero production code is written without a prior failing test. Use when: creating new features, fixing bugs, or expanding test coverage.'

Test-Driven Development (TDD) Standard

Priority: P0 — Iron Law

NO PRODUCTION CODE WITHOUT FAILING TEST FIRST. Code written before test MUST deleted. Start over.

Step 1: RGR Loop (Red-Green-Refactor)

  1. RED: Write minimal failing test. Verify failure (Expected error, not typo).
  2. GREEN: Write simplest code to pass. Verify pass.
  3. REFACTOR: Clean up code while staying green.

AAA Structure (Mandatory)

Every test must follow Arrange-Act-Assert:

  • Arrange: Set up inputs, stubs, mocks, and expected values.
  • Act: Call single unit under test.
  • Assert: Verify output and side effects. One logical assertion per test. (See AAA Example for code structure).

Step 3: Verification & Thresholds

  • Minimum Coverage: 80% (Stat/Func/Line), 75% (Branch).
  • Mocks:
  • Always mock: HTTP, Time/Date, Filesystem.
  • Never mock: Fast internal services (<200ms), pure domain logic.
  • See Test Runner Reference for environment-specific commands.

Step 4: Principles & Mocks

  • Watch it Fail: Prove test works before writing code.
  • Minimalism: Don't add features/options beyond current test (YAGNI).
  • Isolation: Mock external APIs (HTTP) and Time.
  • Realism: Prefer real DBs (test containers) and fast internal services (<200ms).

Verification Checklist

  • [ ] Every new function/method failing test first?
  • [ ] Failure message expected?
  • [ ] Minimal code implemented passed?
  • [ ] AAA structure followed?
  • [ ] Coverage thresholds met?

Expert References

Anti-Patterns

  • No test-after: Writing tests post-implementation defeats TDD. Delete and restart.
  • No assertion-free tests: test without assert not test.
  • No testing implementation: Test behavior and contracts, not internal calls.