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name: tdd-discipline description: Use when implementing features, fixing bugs, or writing any production code - enforces RED-GREEN-REFACTOR cycle where tests must fail before writing implementation code. Activates before coding begins.

Test-Driven Development

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

Core principle: If you didn't watch the test fail, you don't know if it tests the right thing.

The Iron Law

CopyNO PRODUCTION CODE WITHOUT A FAILING TEST FIRST

Write code before the test? Delete it. Start over.

No exceptions:

• Don't keep it as "reference"
• Don't "adapt" it while writing tests
• Delete means delete

Red-Green-Refactor

RED - Write Failing Test

Write one minimal test showing what should happen. Run it. Watch it fail.

Verify failure is correct:

• Test fails (not errors)
• Fails because feature missing (not typos)
• Failure message matches expectation

GREEN - Minimal Code

Write simplest code to pass the test. Nothing more.

Don't:

• Add features beyond the test
• Refactor other code
• "Improve" beyond what test requires

REFACTOR - Clean Up

After green only:

• Remove duplication
• Improve names
• Extract helpers

Keep tests green. Don't add behavior.

Common Rationalizations

Red Flags - STOP and Start Over

• Code before test
• Test passes immediately (didn't see it fail)
• Can't explain why test failed
• "Just this once"
• "This is different because..."

All of these mean: Delete code. Start over with TDD.

Quick Reference

When Stuck