Test driven development

Skill ComeOnOliver/skillshub/skills/aiskillstore/marketplace/dmjgilbert/test-driven-development

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npx -y skills add ComeOnOliver/skillshub --skill test-driven-development

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Enforce RED-GREEN-REFACTOR cycle. Use when implementing features, fixing bugs, or writing any production code.

SKILL.md

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Test-Driven Development

Write the test first. Watch it fail. Write minimal code to pass.

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Any code written before its corresponding test must be deleted entirely - no exceptions for "reference" or "adapting" existing work.

Red-Green-Refactor Cycle

RED: Write Failing Test

Write ONE minimal failing test demonstrating desired behavior
Use clear naming that describes the behavior
Test real code, not mocks (mock only external dependencies)
Focus on ONE behavior per test

Verify RED (CRITICAL)

Run tests and confirm:

Test fails (not errors)
Failure indicates missing feature
Error message matches expectations

If test passes immediately → DELETE IT (it proves nothing)

GREEN: Make It Pass

Implement the simplest code that passes the test
Avoid over-engineering
Don't add features not requested
Keep scope narrow

Verify GREEN

All tests pass
No other tests broke

REFACTOR: Clean Up

Clean up while ALL tests remain green
Remove duplication (DRY)
Improve naming
Extract helpers if needed

Why Tests-First Matters

Tests written after code pass immediately, proving nothing about their validity. Tests-first:

Force discovery of edge cases before implementation
Provide systematic verification impossible with manual testing
Document expected behavior

Common Rationalizations (ALL REJECTED)

Excuse	Why It's Wrong
"Too simple to test"	Simple code still needs verification
"I'll test after"	Tests-after pass immediately, proving nothing
"Already manually tested"	Manual testing isn't repeatable or documented
"Deleting hours of work is wasteful"	Sunk cost fallacy - untested code is liability

When to Use TDD

Always: New features, bug fixes, refactoring, behavior changes

Exceptions only: Throwaway prototypes, generated code, config files (with permission)

Red Flags Requiring Restart

Code written before test
Test passes immediately
Can't explain why test should fail
Rationalizing "just this once"

→ DELETE the code and recommence with failing test

When 3+ Test Fixes Fail

STOP. This signals an architectural problem:

Return to investigation phase
Question whether the underlying pattern is sound
Discuss with user before attempting more fixes