tdd

name	tdd
description	Test-driven development workflow. Write failing tests first, then implement the minimum code to make them pass. Use when implementing features or fixing bugs.
allowed-tools	Read, Grep, Glob, Bash, Edit, Write

Test-Driven Development

Strict red-green-refactor cycle. Never write implementation before a failing test exists.

Cycle

1. Red — Write a Failing Test

• Understand the requirement or bug to fix
• Write a test that asserts the expected behavior
• Run the test suite — confirm the new test fails
• If it passes, the behavior already exists or the test is wrong

2. Green — Minimum Implementation

• Write the smallest amount of code that makes the failing test pass
• Do not add extra logic, edge case handling, or "nice to have" behavior
• Run the test suite — confirm all tests pass (not just the new one)

3. Refactor — Clean Up (Only If Green)

• Only refactor when all tests are green
• Remove duplication introduced in the Green step
• Improve naming, extract methods — but change no behavior
• Run tests again after refactoring to confirm nothing broke

Rules

• One test at a time. Do not batch-write tests
• Each cycle should be small — if a test requires 50+ lines of implementation, break the requirement into smaller pieces
• For bug fixes: write a test that reproduces the bug before touching any implementation code
• Use the project's existing test framework and conventions
• For Python: prefer pytest
• For Kotlin: prefer JUnit 5 or whatever the project already uses

Verification

After all cycles complete:

1. Run the full test suite
2. Confirm coverage of the new code (if coverage tooling is available)
3. List which tests were added and what they cover