common-tdd

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. (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)

385 stars

Best use case

common-tdd is best used when you need a repeatable AI agent workflow instead of a one-off prompt.

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. (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)

Teams using common-tdd should expect a more consistent output, faster repeated execution, less prompt rewriting.

When to use this skill

  • You want a reusable workflow that can be run more than once with consistent structure.

When not to use this skill

  • You only need a quick one-off answer and do not need a reusable workflow.
  • You cannot install or maintain the underlying files, dependencies, or repository context.

Installation

Claude Code / Cursor / Codex

$curl -o ~/.claude/skills/common-tdd/SKILL.md --create-dirs "https://raw.githubusercontent.com/HoangNguyen0403/agent-skills-standard/main/.agent/skills/common/common-tdd/SKILL.md"

Manual Installation

  1. Download SKILL.md from GitHub
  2. Place it in .claude/skills/common-tdd/SKILL.md inside your project
  3. Restart your AI agent — it will auto-discover the skill

How common-tdd Compares

Feature / Agentcommon-tddStandard Approach
Platform SupportNot specifiedLimited / Varies
Context Awareness High Baseline
Installation ComplexityUnknownN/A

Frequently Asked Questions

What does this skill do?

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. (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)

Where can I find the source code?

You can find the source code on GitHub using the link provided at the top of the page.

Related Guides

SKILL.md Source

# Test-Driven Development (TDD) Standard

## **Priority: P0 — The Iron Law**

> **NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.**
> Code written before the test MUST be deleted. Start over.

## **Step 1: The RGR Loop (Red-Green-Refactor)**

1. **RED**: Write a 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 the single unit under test.
- **Assert**: Verify output and side effects. One logical assertion per test.
  **(See [AAA Example](references/aaa_example.md) 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](references/test_runners.md) for environment-specific commands.

## **Step 4: Principles & Mocks**

- **Watch it Fail**: Prove the 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 has a failing test first?
- [ ] Failure message was expected?
- [ ] Minimal code implemented passed?
- [ ] AAA structure followed?
- [ ] Coverage thresholds met?

## **Expert References**

- [AAA Example](references/aaa_example.md)
- [AAA Methodology](references/aaa_methodology.md)
- [Test Runners](references/test_runners.md)
- [TDD Patterns](references/tdd_patterns.md)
- [Testing Anti-Patterns](references/testing_anti_patterns.md)

## Anti-Patterns

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

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