test-driven-development-codex

Test-Driven Development

Keep Claude in the main thread for user interaction and task acceptance. Call the codex_implement MCP tool with promptTemplate: "tdd" for TDD-disciplined implementation. Use codex_resume for fix loops if TDD discipline is violated. Reference testing-anti-patterns.md when reviewing Codex output for testing quality.

Overview

Tests written after code prove nothing — passing tests don't confirm they test the right thing.

Core principle: NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.

Announce at start: "I'm using the test-driven-development skill to implement this with strict red-green-refactor discipline."

The Iron Law

If you didn't watch the test fail, you don't know if it tests the right thing.

If Codex returns implementation without red-green evidence, reject it and resume with TDD enforcement.

When to Use

• Any implementation task where test coverage is critical
• New features, bug fixes, refactors where behavior must be verified
• When the user explicitly requests TDD methodology

Workflow

Step 1: Verify Task Readiness

• Task has clear acceptance criteria
• Test framework is identified (check existing test files)
• Codex CLI is available

If acceptance criteria are unclear, ask the user before dispatching.

Step 2: Call codex_implement with TDD Prompt Template

Call the codex_implement MCP tool with promptTemplate: "tdd":

{
  "tool": "codex_implement",
  "arguments": {
    "taskId": "task-17",
    "promptTemplate": "tdd",
    "prompt": "Implement the requested behavior with strict red-green-refactor discipline. Write the failing test first, then the minimal production change, then refactor only if the tests still pass.",
    "workspaceRoot": "/absolute/path/to/your/repo"
  }
}