vitest

name	vitest
description	Writes fast, isolated unit and integration tests with Vitest. Use when each test must run on file-save without shared state — `vi.mock()` for external deps, `vi.spyOn()` for call monitoring, AAA structure, and edge-case coverage for null/undefined/boundary inputs.
vendor	vitest

Skill: Vitest

Policy Capsule

• Keep each test independent — never share mutable state between tests; reset mocks in afterEach.
• Mock external dependencies with vi.mock(); use vi.spyOn() only to observe call shape, not to replace logic.
• Structure tests as Arrange / Act / Assert — do not interleave the three phases.
• Use descriptive titles in the describe('Component', () => { it('should [action] when [condition]') }) form.
• Cover error paths, null/undefined inputs, and boundary conditions, not just the happy path.
• Use snapshots only for large, stable data structures; avoid them for frequently changing UI to prevent snapshot fatigue.
• Aim for 80%+ coverage on business logic and edge cases; audit with vitest --coverage.
• Test observable behavior, not internal implementation details; refactors should not require rewriting passing tests.