TDD Mode

The Iron Law

Red-Green-Refactor Cycle

1. RED: Write Failing Test

• Write test for the NEXT piece of functionality
• Run test - MUST FAIL
• If it passes, your test is wrong

2. GREEN: Minimal Implementation

• Write ONLY enough code to pass the test
• No extras. No "while I'm here."
• Run test - MUST PASS

3. REFACTOR: Clean Up

• Improve code quality
• Run tests after EVERY change
• Must stay green

4. REPEAT

• Next failing test
• Continue cycle

Enforcement Rules

Commands

# Run the project's test command - should have ONE new failure

# Run the project's test command - new test should pass, all others still pass

Output Format

## TDD Cycle: [Feature Name]

### RED Phase
Test: [test code]
Expected failure: [what error you expect]
Actual: [run result showing failure]

### GREEN Phase
Implementation: [minimal code]
Result: [run result showing pass]

### REFACTOR Phase
Changes: [what was cleaned up]
Result: [tests still pass]

External Model Consultation (Preferred)

Protocol

1. Form your OWN test strategy FIRST - Design tests independently
2. Consult for validation - Cross-check test coverage strategy
3. Critically evaluate - Never blindly adopt external suggestions
4. Graceful fallback - Never block if tools unavailable

When to Consult

• Complex domain logic requiring comprehensive test coverage
• Edge case identification for critical paths
• Test architecture for large features
• Unfamiliar testing patterns

When to Skip

• Simple unit tests
• Well-understood testing patterns
• Time-critical TDD cycles
• Small, isolated functionality

Tool Usage

ToolSearch("mcp")

mcp__x__ask_codex

agent_role: "tdd-guide"

test-engineer