# Tdd Red

> Execute the RED phase of TDD by writing a failing test for the next unmarked item in PLAN.md. Writes tests with Korean descriptions and confirms test failure.

- Skill: `majiayu000/tdd-red` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add majiayu000/tdd-red`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/tdd-red/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/tdd-red

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# TDD RED Phase

## Overview

This skill executes the RED phase of Test-Driven Development. It finds the next unmarked test in PLAN.md, writes a failing test that describes the desired behavior, and confirms the test fails as expected.

## When to Use

Use this skill when:
- Starting a new TDD cycle
- Ready to write the next failing test
- Following the TDD RED → GREEN → REFACTOR cycle
- Implementing a feature listed in PLAN.md

## Workflow

### Step 1: Locate Next Test

**Find the Test:**
1. Read PLAN.md to find the next unmarked test (without [x] or [ ])
2. If PLAN.md doesn't exist or is empty, ask the user what test to write
3. Understand the behavior being tested

**Mark the Test:**
- Mark the test with [ ] in PLAN.md to indicate it's in progress

### Step 2: Write the Failing Test

**Test Characteristics:**
- Has a clear, descriptive name that describes the behavior
- Uses Korean (ko-KR) for test descriptions as specified in LANG.md
- Tests only ONE small increment of functionality
- Will fail because the feature isn't implemented yet
- Uses meaningful assertions that clearly show expected vs actual

**Follow TDD Principles:**
- Write the SIMPLEST test that will fail
- Don't write production code yet
- Focus on defining the desired behavior
- Make the test expressive and easy to understand

### Step 3: Confirm RED Phase

**Run the Test:**
1. Execute the test suite (excluding long-running tests)
2. Confirm the new test fails for the RIGHT reason
3. Verify all other existing tests still pass
4. Check there are no compilation errors or warnings

**Report Results:**
- Show the failing test output
- Confirm we are in RED phase
- Prepare to move to GREEN phase

## Important Reminders

- **DO NOT** implement any production code in this phase
- **DO NOT** make existing tests pass - only write new failing test
- **ONLY** write ONE test at a time
- The test should fail because functionality is missing, not due to syntax errors
- Test name should clearly communicate what behavior is being tested

## Next Steps

After completing RED phase:
1. Verify the test fails for the expected reason
2. Move to GREEN phase to implement minimum code
3. Do not skip directly to implementation - follow the cycle