---
name: tdd-workflow
description: "Test-Driven Development workflow principles. RED-GREEN-REFACTOR cycle."
risk: critical
source: community
date_added: "2026-02-27"
---

# TDD Workflow

> Write tests first, code second.

---

## 1. The TDD Cycle

```
🔴 RED → Write failing test
    ↓
🟢 GREEN → Write minimal code to pass
    ↓
🔵 REFACTOR → Improve code quality
    ↓
   Repeat...
```

---

## 2. The Three Laws of TDD

1. Write production code only to make a failing test pass
2. Write only enough test to demonstrate failure
3. Write only enough code to make the test pass

---

## 3. RED Phase Principles

### What to Write

| Focus | Example |
|-------|---------|
| Behavior | "should add two numbers" |
| Edge cases | "should handle empty input" |
| Error states | "should throw for invalid data" |

### RED Phase Rules

- Test must fail first
- Test name describes expected behavior
- One assertion per test (ideally)

---

## 4. GREEN Phase Principles

### Minimum Code

| Principle | Meaning |
|-----------|---------|
| **YAGNI** | You Aren't Gonna Need It |
| **Simplest thing** | Write the minimum to pass |
| **No optimization** | Just make it work |

### GREEN Phase Rules

- Don't write unneeded code
- Don't optimize yet
- Pass the test, nothing more

---

## 5. REFACTOR Phase Principles

### What to Improve

| Area | Action |
|------|--------|
| Duplication | Extract common code |
| Naming | Make intent clear |
| Structure | Improve organization |
| Complexity | Simplify logic |

### REFACTOR Rules

- All tests must stay green
- Small incremental changes
- Commit after each refactor

---

## 6. AAA Pattern

Every test follows:

| Step | Purpose |
|------|---------|
| **Arrange** | Set up test data |
| **Act** | Execute code under test |
| **Assert** | Verify expected outcome |

---

## 7. When to Use TDD

| Scenario | TDD Value |
|----------|-----------|
| New feature | High |
| Bug fix | High (write test first) |
| Complex logic | High |
| Exploratory | Low (spike, then TDD) |
| UI layout | Low |

---

## 8. Test Prioritization

| Priority | Test Type |
|----------|-----------|
| 1 | Happy path |
| 2 | Error cases |
| 3 | Edge cases |
| 4 | Performance |

---

## 9. Anti-Patterns

| ❌ Don't | ✅ Do |
|----------|-------|
| Skip the RED phase | Watch test fail first |
| Write tests after | Write tests before |
| Over-engineer initial | Keep it simple |
| Multiple asserts | One behavior per test |
| Test implementation | Test behavior |

---

## 10. AI-Augmented TDD

### Multi-Agent Pattern

| Agent | Role |
|-------|------|
| Agent A | Write failing tests (RED) |
| Agent B | Implement to pass (GREEN) |
| Agent C | Optimize (REFACTOR) |

---

> **Remember:** The test is the specification. If you can't write a test, you don't understand the requirement.

## When to Use
This skill is applicable to execute the workflow or actions described in the overview.

## Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.