Test-Driven Development

This skill is guidance, not a script. Build one behavior at a time: red, green, refactor. Use the authorized outcome and existing interfaces; TDD does not expand the task or apply to every kind of edit.

When not to use

• A test that is flaky or controls shared resources, clocks, or subprocesses. Use test-reliability.
• A behavior with no clear interface or observable result. Clarify it first.
• A one-line fix whose existing test already fails for the intended reason.

Inputs and authorization

• Required: one caller-visible behavior and the stable interface it goes through.
• Authorization: TDD does not widen the task; test-first applies only within the authorized behavior.

Method

Red