Agent Skills: accelint-ts-testing

Comprehensive vitest testing guidance for TypeScript projects. Use when (1) Writing new tests with AAA pattern, parameterized tests, or async/await, (2) Reviewing test code for anti-patterns like loose assertions (toBeTruthy), over-mocking, or nested describe blocks, (3) Optimizing slow test suites, (4) Implementing property-based testing with fast-check - especially for encode/decode pairs, roundtrip properties, validators, normalizers, and idempotence checks. Covers test organization, assertions, test doubles hierarchy (fakes/stubs/mocks), async testing, performance patterns, and property-based testing patterns. Trigger keywords on vitest, *.test.ts, describe, it, expect, vi.mock, fast-check, fc.property, roundtrip, idempotence.