Information Density: Vitest – Signal Evidence & AI Readability

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Announcing Vite+ Alpha: Open source. Unified. Next-gen.Are you an LLM? View /llms.txt for optimized Markdown documentation, or /llms-full.txt for full documentation bundleBy
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[H1] Next Generation Testing Framework
A Vite-native testing framework. It's fast! Get Started View on GitHub
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Why Vitest
[H3] The Vite Native Test Runner
Learn more Vitest was created to make testing just work for Vite apps. By building on top of Vite, Vitest natively understands your Vite config and is able to reuse the same resolve and transform pipelines. You can also use Vitest even if you are not using Vite. It is Jest-compatible and works for backend code too. Learn more
[H2] Fast. Lightweight. Integrated.
[H5] Vite Powered
Reuse Vite's config and plugins - consistent across your app and tests. But it's not required to use Vitest!
[H5] Jest Compatible
Expect, snapshot, coverage, and more - migrating from Jest is straightforward.
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[H5] Smart & instant watch mode
Only rerun the related changes, just like HMR for tests!
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[H5] ESM, TypeScript, JSX
Out-of-box ESM, TypeScript and JSX support powered by Oxc. See full features list
[H3] Free & open source
Vitest is free and open source, made possible by wonderful sponsors.Become a Sponsor
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Are you an LLM? You can read better optimized documentation at /guide.md for this page in Markdown format
[H1] Getting Started ​
[H2] Overview ​
Vitest (pronounced as "veetest") is a next generation testing framework powered by Vite.You can learn more about the rationale behind the project in the Why Vitest section.
[H2] Trying Vitest Online ​
You can try Vitest online on StackBlitz. It runs Vitest directly in the browser, and it is almost identical to the local setup but doesn't require installing anything on your machine.
[H2] Adding Vitest to Your Project ​
Learn how to install by Videonpmyarnpnpmbunbashnpm install -D vitestbashyarn add -D vitestbashpnpm add -D vitestbashbun add -D vitestTIPVitest requires Vite >=v6.0.0 and Node >=v20.0.0It is recommended that you install a copy of vitest in your package.json, using one of the methods listed above. However, if you would prefer to run vitest directly, you can use npx vitest (the npx tool comes with npm and Node.js).The npx tool will execute the specified command. By default, npx will first check if the command exists in the local project's binaries. If it is not found there, npx will look in the system's $PATH and execute it if found. If the command is not found in either location, npx will install it in a temporary location prior to execution.
[H2] Writing Tests ​
As an example, we will write a simple test that verifies the output of a function that adds two numbers.sum.jsexport function sum(a, b) {
return a + b
}sum.test.jsimport { expect, test } from 'vitest'
import { sum } from './sum.js'
test('adds 1 + 2 to equal 3', () => {
expect(sum(1, 2)).toBe(3)
})TIPBy default, tests must contain .test. or .spec. in their file name.Next, in order to execute the test, add the following section to your package.json:package.jsonjson{
"scripts": {
"test": "vitest"
}
}Finally, run npm run test, yarn test or pnpm test, depending on your package manager, and Vitest will print this message:txt✓ sum.test.js (1)
✓ adds 1 + 2 to equal 3
Test Files 1 passed (1)
Tests 1 passed (1)
Start at 02:15:44
Duration 311msWARNINGIf you are using Bun as your package manager, make sure to use bun run test command instead of bun test, otherwise Bun will run its own test runner.Your first test is passing! Continue to Writing Tests to learn about organizing tests, reading test output, and the core testing patterns you'll use every day.To run tests once without watching for file changes, use vitest run. You can also pass additional flags like --reporter or --coverage. For a full list of CLI options, run npx vitest --help or see the CLI guide.
[H2] Configuring Vitest ​
Vitest reads your vite.config.* by default, so your existing Vite plugins and configuration work out-of-the-box. You can also create a dedicated vitest.config.* for test-specific settings. See the Config Reference for details.
[H2] IDE Integrations ​
We also provided an official extension for Visual Studio Code to enhance your testing experience with Vitest.Install from VS Code MarketplaceLearn more about IDE Integrations
[H2] Examples ​
ExampleSourcePlaygroundbasicGitHubPlay OnlinefastifyGitHubPlay Onlinein-source-testGitHubPlay OnlinelitGitHubPlay OnlinevueGitHubPlay OnlinemarkoGitHubPlay OnlinepreactGitHubPlay OnlineqwikGitHubPlay OnlinereactGitHubPlay OnlinesolidGitHubPlay OnlinesvelteGitHubPlay OnlineprofilingGitHubNot AvailabletypecheckGitHubPlay OnlineprojectsGitHubPlay Online
[H2] Community ​
If you have questions or need help, reach out to the community at Discord and GitHub Discussions.

Are you an LLM? You can read better optimized documentation at /api/test.md for this page in Markdown format
[H1] Test ​
Alias: ittsfunction test(
name: string | Function,
body?: () => unknown,
timeout?: number
): void
function test(
name: string | Function,
options: TestOptions,
body?: () => unknown,
): voidtest or it defines a set of related expectations. It receives the test name and a function that holds the expectations to test.Optionally, you can provide a timeout (in milliseconds) for specifying how long to wait before terminating, or a set of additional options. The default timeout is 5 seconds, and can be configured globally with testTimeout.tsimport { expect, test } from 'vitest'
test('should work as expected', () => {
expect(Math.sqrt(4)).toBe(2)
})WARNINGIf the first argument is a function, its name property will be used as the name of the test. The function itself will not be called.If test body is not provided, the test is marked as todo.When a test function returns a promise, the runner will wait until it is resolved to collect async expectations. If the promise is rejected, the test will fail.TIPIn Jest, TestFunction can also be of type (done: DoneCallback) => void. If this form is used, the test will not be concluded until done is called. You can achieve the same using an

Are you an LLM? You can read better optimized documentation at /config.md for this page in Markdown format
[H1] Configuring Vitest ​
If you are using Vite and have a vite.config file, Vitest will read it to match with the plugins and setup as your Vite app. If you want to have a different configuration for testing or your main app doesn't rely on Vite specifically, you could either:Create vitest.config.ts, which will have the higher priority and will override the configuration from vite.config.ts (Vitest supports all conventional JS and TS extensions, but doesn't support json) - it means all options in your vite.config will be ignoredPass --config option to CLI, e.g. vitest --config ./path/to/vitest.config.tsUse process.env.VITEST or mode property on defineConfig (will be set to test/benchmark if not overridden with --mode) to conditionally apply different configuration in vite.config.ts. Note that like any other environment variable, VITEST is also exposed on import.meta.env in your testsTo configure vitest itself, add test property in your Vite config. You'll also need to add a reference to Vitest types using a triple slash command at the top of your config file, if you are importing defineConfig from vite itself.If you are not using vite, add defineConfig imported from vitest/config to your config file:vitest.config.jsjsimport { defineConfig } from 'vitest/config'
export default defineConfig({
test: {
// ... Specify options here.
},
})If you have a vite config already, you can add /// <reference types="vitest/config" /> to include the test types:vite.config.jsjs/// <reference types="vitest/config" />
import { defineConfig } from 'vite'
export default defineConfig({
test: {
// ... Specify options here.
},
})You can retrieve Vitest's default options to expand them if needed:vitest.config.jsjsimport { configDefaults, defineConfig } from 'vitest/config'
export default defineConfig({
test: {
exclude: [...configDefaults.exclude, 'packages/template/*'],
},
})When using a separate vitest.config.js, you can also extend Vite's options from another config file if needed:vitest.config.jsjsimport { defineConfig, mergeConfig } from 'vitest/config'
import viteConfig from './vite.config'
export default mergeConfig(viteConfig, defineConfig({
test: {
exclude: ['packages/template/*'],
},
}))If your Vite config is defined as a function, you can define the config like this:vitest.config.jsjsimport { defineConfig, mergeConfig } from 'vitest/config'
import viteConfig from './vite.config'
export default defineConfig(configEnv => mergeConfig(
viteConfig(configEnv),
defineConfig({
test: {
exclude: ['packages/template/*'],
},
})
))Since Vitest uses Vite config, you can also use any configuration option from Vite. For example, define to define global variables, or resolve.alias to define aliases - these options should be defined on the top level, not within a test property.
[H2] Automatic Dependency Installation ​
Vitest will prompt you to install certain dependencies if they are not already installed. You can disable this behavior by setting the VITEST_SKIP_INSTALL_CHECKS=1 environment variable.
[H2] Config Options ​
Configuration options that are not supported inside a project config have icon next to them. This means they can only be set in the root Vitest config.