Vitest
Vitest fast unit testing framework powered by Vite with Jest-compatible API. Use when writing tests, mocking, configuring coverage, or working with test filtering and fixtures.From its SKILL.md
npx -y skills add antfu/skills --skill vitestAssembled from the repository path, not quoted from the project. Check it against their README if it does not work.
SKILL.md
3.6 KB, 738 tokens by cl100k_base, as published. Nobody here has run it
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.
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 for parallel test execution
- Built-in coverage via V8 or Istanbul
- Snapshot testing, mocking, and spy utilities
The skill is based on Vitest 5.x (beta), generated at 2026-06-22.
Core
| Topic | Description | Reference |
|---|---|---|
| Configuration | Vitest and Vite config integration, defineConfig usage | core-config |
| CLI | Command line interface, commands and options | core-cli |
| Test API | test/it function, modifiers like skip, only, concurrent | core-test-api |
| Describe API | describe/suite for grouping tests and nested suites | core-describe |
| Expect API | Assertions with toBe, toEqual, matchers and asymmetric matchers | core-expect |
| Hooks | beforeEach, afterEach, beforeAll, afterAll, aroundEach | core-hooks |
Features
| Topic | Description | Reference |
|---|---|---|
| Mocking | Mock functions, modules, timers, dates with vi utilities | features-mocking |
| Snapshots | Snapshot testing with toMatchSnapshot and inline snapshots | features-snapshots |
| Coverage | Code coverage with V8 or Istanbul providers | features-coverage |
| Test Context | Test fixtures, context.expect, test.extend for custom fixtures | features-context |
| Concurrency | Concurrent tests, parallel execution, sharding | features-concurrency |
| Filtering | Filter tests by name, file patterns, tags | features-filtering |
| Test Tags | Label tests with tags to filter runs and apply shared options | features-test-tags |
| Reporters | Built-in reporters, default selection, CI/output config | features-reporters |
| Benchmarking | Write benchmarks with the bench fixture (Tinybench) | features-benchmarking |
Advanced
| Topic | Description | Reference |
|---|---|---|
| Vi Utilities | vi helper: mock, spyOn, fake timers, hoisted, waitFor | advanced-vi |
| Environments | Test environments: node, jsdom, happy-dom, 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 |
What ships with it: 20 files
90.5 KB alongside SKILL.md
references/
- advanced-environments.md4.7 KB
- advanced-projects.md5.4 KB
- advanced-type-testing.md4.6 KB
- advanced-vi.md5.6 KB
- core-cli.md4.1 KB
- core-config.md4.7 KB
- core-describe.md3.5 KB
- core-expect.md6.6 KB
- core-hooks.md4.8 KB
- core-test-api.md5.3 KB
- features-benchmarking.md3.6 KB
- features-concurrency.md4.7 KB
- features-context.md5.3 KB
- features-coverage.md4.2 KB
- features-filtering.md3.8 KB
- features-mocking.md6.9 KB
- features-reporters.md3.7 KB
- features-snapshots.md5.2 KB
- features-test-tags.md3.6 KB
- GENERATION.md136 B
Gives 0 of the 12 instructions most unit integration skills give in 738 tokens
Counted across 149 of the 202 authors here whose files we hold, read 2026-09-06
- Structure tests as arrange, act, assertin 17 of 149
- Test behavior, not implementationin 16 of 149
- Mock all external dependenciesin 14 of 149
- Keep tests independentin 9 of 149
- Implement minimal code to passin 7 of 149
- Write a failing test firstin 7 of 149
- Fix or delete flaky tests immediatelyin 7 of 149
- Verify one behaviour per test functionin 7 of 149
- Name tests MethodName_StateUnderTest_ExpectedBehaviorin 6 of 149
- Separate arrange, act, and assert with blank linesin 6 of 149
- Target at least 80 percent core logic coveragein 6 of 149
- Create factory fixtures for test datain 6 of 149
Said here and by no other author read
- consult the reference file for each topic
Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once. Length counted with cl100k_base; the agent that loads this file may tokenize it differently.