vitest by zackbart/skills

Vitest is a next-generation testing framework powered by Vite. It provides a Jest-compatible API with native ESM, TypeScript, and JSX support out of the box. Vitest shares the same config, transformers, resolvers, and plugins with your Vite app.

Requirements: Vite >=v6.0.0, Node >=v20.0.0

Key Features:

Vite-native: Uses Vite's transformation pipeline for fast HMR-like test updates
Jest-compatible: Drop-in replacement for most Jest test suites
Smart watch mode: Only reruns affected tests based on module graph
Native ESM, TypeScript, JSX support without configuration
Multi-threaded workers via node:child_process (default) or node:worker_threads
Built-in coverage via V8 (default) or Istanbul
Snapshot testing, mocking, and spy utilities via Tinyspy
Browser mode for real browser component testing
Benchmarking via Tinybench
In-source testing
Type testing via expect-type
Sharding for CI parallelism

Based on Vitest 4.x (v4.0.17). Key v4 changes: workspace replaced with projects, pool options are top-level, V8 coverage uses AST-based analysis, coverage.all removed, basic reporter removed.

Core

Topic	Description	Reference
Configuration	Vitest and Vite config integration, defineConfig, mergeConfig	core-config
CLI	Command line interface, commands and all options	core-cli
Test API	test/it function, modifiers like skip, only, concurrent, for/each	core-test-api
Describe API	describe/suite for grouping tests and nested suites	core-describe
Expect API	Assertions with toBe, toEqual, matchers, asymmetric matchers, soft/poll	core-expect
Hooks	beforeEach, afterEach, beforeAll, afterAll, aroundEach, aroundAll	core-hooks

Features

Topic	Description	Reference
Mocking	Mock functions, modules, timers, dates, globals with vi utilities	features-mocking
Snapshots	Snapshot testing with file, inline, and file snapshots	features-snapshots
Coverage	Code coverage with V8 or Istanbul providers, thresholds, CI	features-coverage
Test Context	Test fixtures, context.expect, test.extend, scoped fixtures	features-context
Concurrency	Concurrent tests, parallel execution, sharding, CI setup	features-concurrency
Filtering	Filter tests by name, file patterns, tags, changed files	features-filtering

Advanced

Topic	Description	Reference
Vi Utilities	vi helper: mock, spyOn, fake timers, hoisted, waitFor, mockObject	advanced-vi
Environments	Test environments: node, jsdom, happy-dom, edge-runtime, custom	advanced-environments
Type Testing	Type-level testing with expectTypeOf and assertType	advanced-type-testing
Projects	Multi-project workspaces, different configs per project	advanced-projects
Browser Mode	Real browser testing with Playwright, WebdriverIO, or Preview	advanced-browser
Migration	Migrating from Jest and upgrading from Vitest 3.x to 4.x	advanced-migration
Benchmarking	Performance benchmarking with Tinybench integration	advanced-benchmarking
In-Source Testing	Writing tests alongside production code	advanced-in-source
Reporters	Built-in reporters and custom reporter configuration	advanced-reporters
Debugging	VS Code, IntelliJ, Chrome DevTools, inspect flags	advanced-debugging
Vitest UI	Interactive browser UI with module graph and coverage	advanced-ui
Common Errors	Frequent errors and their solutions	advanced-common-errors