Vitest

Vitest is a testing framework. It supports ESM without extra configuration. It integrates with the Vite ecosystem. It has a similar API to Jest.

These features make Vitest a replacement for Jest in sku applications, especially given Jest's current limitations with ESM. Sku supports Vitest as an alternative to Jest since v15.

We recommend using vitest with the vite bundler and in an ESM project. These are not requirements.

Migrating to Vitest

Migrating to Vitest should be straightforward. Before you make any changes, read the Vitest documentation. That documentation covers the API, the features, and the differences between Jest and Vitest.

To enable Vitest in sku, first install the required dependencies:

pnpm add -D vitest

Then, configure testRunner in your sku config:

// sku.config.ts
import type { SkuConfig } from 'sku';

export default {
  testRunner: 'vitest', 
} satisfies SkuConfig;

sku then invokes the vitest CLI instead of the jest CLI when you run sku test.

Key differences between Vitest and Jest

Vitest has strong compatibility with the Jest API. It still has differences that may affect your tests. This page lists the differences that affect sku projects. The Vitest documentation has the full list: Migrating from Jest to Vitest.

To automate most of the migration process, a codemod is available.

NOTE

Additional changes may still be required after running this codemod.

pnpm dlx @sku-lib/codemod jest-to-vitest .

Default Watch Mode

vitest defaults to watch mode when running tests. To run tests without watch mode you can use the --run flag:

// package.json
{
  "scripts": {
    // ...
    "test": "sku test --run"
  }
}

Watch mode does not start in CI environments, so you can omit the flag in your pipeline.

Code Coverage Dependencies

Vitest does not install code coverage dependencies by default. To collect code coverage, pass the --coverage flag to the sku test command. Install the @vitest/coverage-v8 package:

pnpm add -D @vitest/coverage-v8

Testing Library Matchers

If your test setup file includes an import for @testing-library/jest-dom, you may need to change this to @testing-library/jest-dom/vitest:

// test-setup.ts
import '@testing-library/jest-dom'; 
import '@testing-library/jest-dom/vitest'; 

Globals Disabled

Jest enables global APIs such as it, describe, beforeAll, etc., by default. Vitest does not. Sku adopts the Vitest defaults. You need to import these test functions explicitly.

// myFunction.test.ts
import { describe, expect, it } from 'vitest'; 

Because Vitest disables globals, some common libraries like testing-library will not run auto DOM cleanup. If you use these libraries, add cleanup to your configured setupTests file.

import '@testing-library/jest-dom/vitest';

import { cleanup } from '@testing-library/react'; 
import { afterEach } from 'vitest'; 

afterEach(cleanup);