tdd

name	tdd
description	Test-Driven Development skill. Automatically activates on test files. 3-phase protocol: Explore (understand existing tests), Plan (list scenarios), Act (write tests then implementation).
user-invocable	false

TDD Skill

This skill activates automatically when working with test files.

3-Phase Protocol

Phase 1: Explore (Read first, always)

1. Read the test file you are working in
2. Read 1-2 neighboring test files to understand project conventions
3. Identify: test framework, assertion style, mock patterns, fixtures

Phase 2: Plan (List scenarios before writing)

For every function/method you are testing, list:

• Happy path(s)
• Error paths (each throw/rejection)
• Edge cases (null, empty, boundary values, concurrent)

Do not proceed to Phase 3 until all scenarios are listed.

Phase 3: Act (Write tests, then implementation)

TDD order:

1. Write a failing test
2. Write the minimal implementation to make it pass
3. Refactor (don't break the test)

Anti-patterns

• ❌ Writing implementation before tests
• ❌ Tests that pass regardless of implementation
• ❌ Skipping error path tests because "it probably won't happen"
• ❌ Mocking the function under test

Conventions

• Mirror source structure: src/foo/bar.ts → src/foo/bar.test.ts
• Test names: describe behavior, not implementation — "returns null when user not found"
• One concept per test — don't test 3 things in one it block