behavior-driven-development

Use when implementing any feature or bugfix, before writing implementation code. Triggered by keywords: TDD, BDD, test-first, test-driven, write-test-first

Use in a dedicated subagent when completing tasks, implementing major features, or doing post-TDD code review before merge to verify work meets requirements

Use in a dedicated subagent for post-TDD blind unit-test review against requirements and public contracts to find missing cases, wrong assertions, and brittle tests.