TDD Skill

Announce at start: "Using TDD: writing test first for [behavior]."

When to use this skill

• •new features that can be unit tested
• •bug fixes (always add a regression test if practical)
• •refactors (protect behavior with tests first)

Research

Before writing tests, do research in parallel (waitForPreviousTools: false):

• •search_web for the project's testing framework best practices and latest patterns (scope to stack.md versions).
• •search_web for assertion styles and testing utilities available in the framework.

Rules

• •Prefer red -> green -> refactor.
• •If tests are hard, still add verification: minimal repro script, integration test, or clear manual steps.
• •Keep tests focused: one behavior per test where possible.
• •Name tests by behavior, not implementation details.

Process

1. •Define the behavior change (what should be true after).
2. •Write/adjust a test to capture it (make it fail first if possible).
3. •Implement the minimal change to pass.
4. •Refactor if needed (keep passing).
5. •Run the relevant test suite + any linters in parallel where they are independent.

Output requirements

When you change code, include:

• •what tests you added/changed
• •how to run them
• •what they prove

Bite-sized granularity

Each step should be one action (2-5 minutes):

1. •Write the failing test — step
2. •Run it to confirm it fails — step
3. •Implement the minimal code to make it pass — step
4. •Run tests to confirm they pass — step
5. •Commit — step

Don't combine these. Each step is independently verifiable.