Unit Testing

Focused skill for unit-test design — TDD workflow (red-green-refactor), test naming (AAA, Given-When-Then), mocking patterns (mocks/spies/stubs/fakes, dependency injection), and coverage strategy (line vs branch, mutation testing). Composable: invokable standalone (write unit tests for this function, qué mockear aquí, what to mock) or mid-flight from sprint-development for TDD slices. Triggers on: write unit tests, TDD this function, test-driven development, qué mockear aquí, what to mock, test naming, AAA pattern, Given-When-Then, test coverage, branch coverage, Jest, Vitest, unit testing. Do NOT use for: feature implementation orchestration (use /sprint-development), E2…