tdd-iron-law

The Iron Law

NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.

This is not a guideline. It is the floor of the discipline. The Iron Law has exactly one consequence when violated:

Delete the code. Write the test. Start over.

Not "add a test after the fact." Not "promise to add one later." Delete the production code, write the failing test you should have written, then re-derive the implementation under the Red-Green-Refactor cycle. The deletion is not punishment — it is restoration of the feedback loop that the violation disabled.

Grounding (primary sources)

The Iron Law is not a stylistic preference. Four primary sources converge on it:

Beck (2002) Preface — the canonical formulation

Kent Beck, Test-Driven Development: By Example (Addison-Wesley Signature Series), ISBN 978-0321146533, Preface:

"Write the test you wish you had. Make it fail. Make it pass. Make it clean."