vitest-testing

Vitest is a Vite-native unit testing framework that shares the same configuration and plugin ecosystem. Built for speed with native ESM support, hot module replacement for tests, and parallel execution.

When to use: Unit tests, component tests, integration tests, hook tests, in-source tests. Testing React components with React Testing Library. Testing TanStack Query/Router/Form patterns.

When NOT to use: End-to-end testing (use Playwright), visual regression testing (use Percy/Chromatic), load testing (use k6).

Vitest testing framework for unit, component, and integration tests. Covers test structure (describe/it/test.each), assertions with expect, lifecycle hooks, mocking (vi.fn/vi.mock/vi.spyOn), React Testing Library patterns, hook testing with renderHook, user-event interactions, async utilities, configuration, workspace setup, coverage, and advanced patterns like in-source testing and concurrent execution. Also covers CLI commands, test filtering, tags, sharding, fixtures with test.extend, and fixture scoping. Use when writing unit tests, component tests, integration tests, or testing React hooks. Use for test configuration, mocking modules, testing async behavior, snapshot testing, or setting up test coverage. Source: oakoss/agent-skills.