Test-Driven Development Skill

Guidelines for effective Test-Driven Development.

TDD Philosophy

"Write a failing test before you write the code that makes it pass."

• Kent Beck

The TDD Cycle

    ┌─────────┐
    │   RED   │  Write failing test
    └────┬────┘
         │
    ┌────▼────┐
    │  GREEN  │  Write minimal code to pass
    └────┬────┘
         │
    ┌────▼────┐
    │REFACTOR │  Clean up, keep tests green
    └────┬────┘
         │
         └──────► Repeat

RED Phase

Goal

Write a test that FAILS because the code does not exist yet.

Rules

• Test expresses expected behavior
• Test is focused on ONE thing
• Test has meaningful assertions
• Test MUST fail when run

If Test Passes in RED

Something is wrong:

• Code may already exist
• Test may be incorrectly written
• Test may not be testing what you think

Investigate before proceeding.

GREEN Phase

Goal

Write the MINIMUM code to make the test pass.

Rules

• Only write enough to pass the test
• No optimization
• No additional features
• No "while I'm here" changes
• Ugly code is OK

Mantra

"Make it work, make it right, make it fast." (We're in "make it work" phase)

REFACTOR Phase

Goal

Improve code quality while keeping tests green.

Rules

• Run tests after EVERY change
• Small, incremental improvements
• Revert if tests fail
• Stop when code is clean enough

Common Refactorings

• Extract method/function
• Rename for clarity
• Remove duplication
• Apply design patterns
• Add documentation

Framework-Specific Guides

• Laravel Testing
• Flutter Testing
• Vue Testing

When to Use TDD

Always Use TDD For

• Business logic
• Data transformations
• Validation rules
• API endpoints
• Services

Consider Skipping TDD For

• Simple CRUD (test at integration level)
• Configuration code
• Boilerplate/scaffolding
• UI-only changes (use manual testing)

Test Types

Test Pyramid

        /\
       /  \      E2E Tests (few)
      /----\
     /      \    Integration Tests (some)
    /--------\
   /          \  Unit Tests (many)
  /____________\

Coverage Targets

Anti-Patterns

Test After

Writing tests after implementation - you lose the design benefits of TDD.

Testing Implementation

Testing HOW code works instead of WHAT it does.

Over-Mocking

Mocking everything - you're testing your mocks, not your code.

Giant Tests

Tests that test too much - hard to debug when they fail.

Flaky Tests

Tests that sometimes pass, sometimes fail - erode trust in test suite.

Quick Reference

RED Phase Checklist

• Test has descriptive name
• Test is focused on ONE behavior
• Test has clear assertion
• Test FAILS when run

GREEN Phase Checklist

• Code is minimal
• No extra features
• Test PASSES
• No new tests written

REFACTOR Phase Checklist

• Code is cleaner
• Tests still PASS
• No behavior changed
• Ready for next cycle