test-driven-development
Drives development with tests using the red-green-refactor loop. Use when implementing any logic, fixing any bug, or changing any behavior. Use when you need to prove that code works, when a bug report arrives, or when you're about to modify existing functionality.
- Kind
- Skill
- Works with
- Claude Code, Codex, Any agent
- Source
- addyosmani/agent-skills @ 2686b620fc1f
- Path
- skills/test-driven-development/SKILL.md
- License
- MIT
- Jobs
- Testing, Implementation
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# Test-Driven Development ## Overview Write a failing test before writing the code that makes it pass. For bug fixes, reproduce the bug with a test before attempting a fix. Tests are proof — "seems right" is not done. A codebase with good tests is an AI agent's superpower; a codebase without tests is a liability. ## When to Use - Implementing any new logic or behavior - Fixing any bug (the Prove-It Pattern) - Modifying existing functionality - Adding edge case handling - Any change that could break existing behavior **When NOT to use:** Pure configuration changes, documentation updates, or static content changes that have no behavioral impact. **Related:** For browser-based changes, combine TDD with runtime verification using Chrome DevTools MCP — see the Browser Testing section below. ## Discover the Stack First The TDD cycle is universal; the commands are not. Before writing the first test, discover how *this* repository tests, and use its commands for every RED, GREEN, and verification step: - **Language and build system** — `package.json`, `pom.xml`/`build.gradle`, `pyproject.toml`, `go.mod`, `Cargo.toml`, `Gemfile`, a `Makefile` …