---
name: tdd
description: Implement an assigned behavior at the Plan's agreed test seam using red, green, and focused verification.
disable-model-invocation: true
metadata:
  relayview-display-name: Test-driven development
  relayview-version: 0.3.0
---

# Test-driven development

Use the test seams and behavior specified by the immutable Plan. Read the target repository's domain language and test conventions. If the Plan leaves a consequential seam unclear, report that gap to the owner; do not create a new acceptance boundary by silently choosing one.

At each seam, write one test that fails for the missing behavior and observe the failure. Implement the smallest production slice that makes it pass. Repeat for the next behavior, then run the focused checks required by the Plan. Assert observable behavior through public interfaces, using expected values independent of the implementation. Avoid private-method assertions, tautological expectations, and a batch of tests for behavior not yet explored. Record the red and green evidence in the implementation handoff.