test-driven-development
Drives development with tests. 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.
npx skills add addyosmani/agent-skills --skill test-driven-development --agent claude-code
Same command for any agent — swap --agent for codex, cursor, copilot.
Weekly change comes from our own snapshots, not the repository page — it measures attention, not adoption.
# 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` - **Checked-in wrappers** — prefer `./gradlew`,
- Overview
- When to Use
- Discover the Stack First
- The TDD Cycle
- Step 1: RED — Write a Failing Test
- Step 2: GREEN — Make It Pass
- Step 3: REFACTOR — Clean Up
- The Prove-It Pattern (Bug Fixes)
- The Test Pyramid
- Test Sizes (Resource Model)
- Decision Guide
- Writing Good Tests
- Test State, Not Interactions
- DAMP Over DRY in Tests
What does the test-driven-development skill do?
Drives development with tests. 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.
How do I install it?
Run `npx skills add addyosmani/agent-skills --skill test-driven-development --agent claude-code` — it drops the skill into your project so the agent can pick it up. Swap the --agent value for codex, cursor or copilot if you use one of those.
Where does this skill come from?
From addyosmani/agent-skills, a repository with 81,574 stars. We read it straight from the repository tree rather than a submitted listing, so what you see here is what is actually published.
Is a popular skill a good skill?
Not necessarily. Stars measure attention, not adoption — a repository can trend for a week and be abandoned. That is why we show the weekly change from our own snapshots next to the total, instead of a single flattering number.