What problem does it solve? Writing unit tests often produces suites that break on every refactor, pass on real bugs, or assert nothing meaningful. This Skill provides a disciplined workflow for deciding what to test, structuring tests, and verifying they actually catch failures. ## Core Features & Use Cases - Behavior-first test planning: Enumerate observable behaviors rather than methods, producing one test per behavior with names that read as bug reports. - Structured test authoring: Enforces Arrange-Act-Assert layout, outcome-based assertions, builder/factory patterns, and boundary-case parameterization. - Red-check verification: Requires each test to be seen failing with a readable message, and flags anti-patterns like sleeps, real time, and shared mutable fixtures. - Use Case: When writing tests for a billing function like split_bill, the Skill guides you to derive a behavior list (even split, remainder distribution, zero-people error, rounding), producing six targeted tests that caught a real cent-rounding bug. ## Quick Start Ask the AI to write unit tests for your function using behavior-based design with Arrange-Act-Assert structure and red-check verification.
