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

TDD Workflow

Write tests first, code second.

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1. The TDD Cycle

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

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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

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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)

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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

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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

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6. AAA Pattern

Every test follows:

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

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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 |

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8. Test Prioritization

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

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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 |

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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) |

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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.