Tdd

Test-First / Agentic TDD Playbook

This skill enforces strict Test-Driven Development (TDD) methodologies to prevent "vibe coding" and ensure correctness, regression protection, and clear specifications.

Target Triggers

• /tdd
• "implement feature with test-first"
• "write test first"

TDD Workflow Protocol

You must execute the standard Red-Green-Refactor loop systematically:

1. Requirements Discovery & Test Setup

• Identify the target framework, language, testing library (e.g., Jest, PyTest, Vitest, Go testing, RSpec, Mocha, JUnit, pytest-django).
• Locate the existing tests or find the correct directory structure for test files.
• Identify the expected API contract, function signature, or database constraints.

2. Write Failing Tests (Red Phase)

• Write unit or integration tests representing the target feature, endpoint, or bug fix.
• Ensure the tests cover:
  • Happy paths (successful requests, valid parameters, authenticated flows).
  • Edge cases (null/undefined inputs, empty strings, negative bounds, extremely large payloads).
  • Error states (missing headers, unauthorized access, database constraint violations, invalid parameter types).
• Run the test suite and confirm that the new test fails (RED). Note the error message to verify it fails for the expected reason (e.g., "function undefined" or "status code 404").

[!IMPORTANT] Do NOT write any implementation code before demonstrating a failing test. If you skip this, you violate the TDD protocol.

3. Implement Minimum Code (Green Phase)

• Implement only the minimal logic required to make the failing test pass.
• Do not add extra unrequested features or over-engineer the code.
• Run the test suite. If it still fails, adjust the minimal implementation until it is green (PASS).

4. Clean & Refactor (Refactor Phase)

• Review the newly added code for readability, performance, naming conventions, and compliance with the design system.
• Remove duplication, ensure proper typing/schema definitions, and ensure separation of concerns.
• Re-run all tests to verify that the refactoring did not break any functionality.