features.md

Features

Shared config between test, dev and build

Vite's config, transformers, resolvers, and plugins. Use the same setup from your app to run the tests

Watch Mode

Smart & instant watch mode, like HMR for tests!

$ vitest -w

Vitest smartly searches the module graph and only rerun the related tests (just like how HMR works in Vite!).

vitest, vitest dev and vitest watch are aliases and they all start vitest in watch mode by default. They also depend on the CI environment variable, which if it appears to be defined, Vitest is going to run the tests only one time and not in watch mode, like vitest run.

Smooth integration with UI Frameworks

Components testing for Vue, React, Svelte, Lit and more

Common web idioms out-of-the-box

Out-of-box TypeScript / JSX support / PostCSS

ESM first

ESM first, top level await

Threads

Workers multi-threading via tinypool (a lightweight fork of Piscina), allowing tests to run simultaneously. Threads are enabled by default Vitest, and can be disabled passing --no-threads in the CLI.

Vitest also isolates each file's environment so env mutations in one file don't affect others. Isolation can be disabled by passing --no-isolate to the CLI (trading of correctness for run performance).

Filtering

Filtering, timeouts, concurrent for suite and tests

CLI

You can use CLI to filter test files by name:

$ vitest basic

Will only execute test files that contain basic, e.g.

basic.test.ts
basic-foo.test.ts

Specifying a Timeout

You can optionally pass a timeout in milliseconds as third argument to tests. The default is 5 seconds.

import { test } from 'vitest'

test('name', async () => { ... }, 1000)

Hooks also can receive a timeout, with the same 5 seconds default.

import { beforeAll } from 'vitest'

beforeAll(async () => { ... }, 1000)

Skipping suites and tests

Use .skip to avoid running certain suites or tests

import { describe, assert, it } from 'vitest';

describe.skip("skipped suite", () => {
  it("test", () => {
    // Suite skipped, no error
    assert.equal(Math.sqrt(4), 3);
  });
});

describe("suite", () => {
  it.skip("skipped test", () => {
    // Test skipped, no error
    assert.equal(Math.sqrt(4), 3);
  });
});

Selecting suites and tests to run

Use .only to only run certain suites or tests

import { describe, assert, it } from 'vitest'

// Only this suite (and others marked with only) are run
describe.only("suite", () => {
  it("test", () => {
    assert.equal(Math.sqrt(4), 3);
  });
});

describe("another suite", () => {
  it("skipped test", () => {
    // Test skipped, as tests are running in Only mode
    assert.equal(Math.sqrt(4), 3);
  });

  it.only("test", () => {
    // Only this test (and others marked with only) are run
    assert.equal(Math.sqrt(4), 2);
  });
});

Unimplemented suites and tests

Use .todo to stub suites and tests that should be implemented

import { describe, it } from 'vitest'

// An entry will be shown in the report for this suite
describe.todo("unimplemented suite");

// An entry will be shown in the report for this test
describe("suite", () => {
  it.todo("unimplemented test");
});

Running tests concurrently

Use .concurrent in consecutive tests to run them in parallel

import { describe, it } from 'vitest'

// The two tests marked with concurrent will be run in parallel
describe("suite", () => {
  it("serial test", async () => { /* ... */ });
  it.concurrent("concurrent test 1", async () => { /* ... */ });
  it.concurrent("concurrent test 2", async () => { /* ... */ });
});

If you use .concurrent in a suite, every tests in it will be run in parallel

import { describe, it } from 'vitest'

// All tests within this suite will be run in parallel
describe.concurrent("suite", () => {
  it("concurrent test 1", async () => { /* ... */ });
  it("concurrent test 2", async () => { /* ... */ });
  it.concurrent("concurrent test 3", async () => { /* ... */ });
});

You can also use .skip, .only, and .todo with concurrent suites and tests. Read more in the API Reference

Snapshot

Jest Snapshot support

Chai and Jest expect compatibility

Chai built-in for assertions plus Jest expect compatible APIs

Notice that if you are using third-party libraries that add matchers, setting test.globals to true will provide better compatibility

Mocking

Tinyspy built-in for mocking with jest compatible APIs on vi object.

import { vi, expect } from 'vitest'

const fn = vi.fn()

fn('hello', 1)

expect(vi.isMockFunction(fn)).toBe(true)
expect(fn.mock.calls[0]).toEqual(['hello', 1])

fn.mockImplementation((arg) => arg)

fn('world', 2)

expect(fn.mock.returns[1]).toBe('world')

Vitest supports both happy-dom or jsdom for mocking DOM and browser APIs. They don't come with Vitest, you might need to install them:

$ npm i -D happy-dom
# or
$ npm i -D jsdom

After that, change the environment option in your config file:

// vite.config.ts
import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    environment: 'happy-dom' // or 'jsdom', 'node'
  }
})

Coverage

Vitest supports Native code coverage via c8

{
  "scripts": {
    "test": "vitest",
    "coverage": "vitest run --coverage"
  }
}

To configure it, set test.coverage options in your config file:

// vite.config.ts
import { defineConfig } from 'vitest/config'

export default defineConfig({
  test: {
    coverage: {
      reporter: ['text', 'json', 'html']
    }
  }
})