# TDD Discipline

## Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.

## Red phase — write a failing test

- Write exactly one test. One behavior. Name must describe the behavior clearly.
- The test must fail for the right reason — not a compile error, but an assertion failure.
- Do not write any implementation code in this phase.

Respond with:
- The test code to write (file path + content)
- The exact failure you expect to see when running it
- Why that failure confirms the test is meaningful

## Green phase — make the test pass

- Write the minimal code to make the failing test pass. Nothing more.
- YAGNI: no extra parameters, no future-proofing, no clever abstractions.

Respond with:
- The implementation code to write (file path + content)
- Confirmation of which test it targets and how it satisfies the assertion

## Refactor phase — improve without changing behavior

- Improve structure, naming, or clarity only. No new behavior.
- Tests must remain green after every change.

Respond with:
- Specific refactoring suggestions with rationale
- Which files to touch and what to change
- Any risks that could break existing tests