vitest

What is vitest?

Vitest is a blazing fast unit test framework powered by Vite. It is designed to provide a delightful testing experience with features like native ES modules support, TypeScript support, and a rich API for running and organizing tests.

What are vitest's main functionalities?

Unit Testing

Vitest allows you to write and run unit tests for your JavaScript/TypeScript code. The example shows a simple test suite for a math operation.

import { describe, it, expect } from 'vitest';
describe('math', () => {
  it('should add numbers correctly', () => {
    expect(1 + 1).toBe(2);
  });
});

Mocking

Vitest provides a built-in mocking utility, allowing you to create mock functions and spy on their behavior.

import { vi } from 'vitest';
const mockFunction = vi.fn(() => 42);
mockFunction();
expect(mockFunction).toHaveBeenCalled();

Snapshot Testing

Vitest supports snapshot testing, which is useful for ensuring your UI does not change unexpectedly. It saves the 'snapshot' of the output and compares it against future test runs.

import { expect, test } from 'vitest';
test('snapshot test', () => {
  const user = { id: 1, name: 'John Doe' };
  expect(user).toMatchSnapshot();
});

Code Coverage

Vitest can generate code coverage reports to help you understand which parts of your codebase are covered by tests.

// Run Vitest with the --coverage flag to generate code coverage reports
// vitest run --coverage

Watch Mode

Vitest's watch mode re-runs tests when it detects changes in the test files or the corresponding source files, providing instant feedback during development.

// Run Vitest in watch mode using the --watch flag
// vitest --watch

Other packages similar to vitest

jest

Jest is a popular testing framework with a focus on simplicity. It provides a similar set of features to Vitest, including mocking, snapshot testing, and watch mode. However, Jest is often considered slower than Vitest due to its heavier architecture.

mocha

Mocha is a flexible testing framework for Node.js and the browser. It's known for its simplicity and support for various assertion libraries. Unlike Vitest, Mocha does not include a built-in assertion library or mocking utilities, requiring additional packages for these features.

ava

AVA is a test runner for Node.js with a concise API, detailed error output, and process isolation for concurrent test execution. It differs from Vitest in its approach to concurrency and its minimalistic design.

jasmine

Jasmine is a behavior-driven development framework for testing JavaScript code. It does not require a DOM and comes with an assertion library. Jasmine is less modern compared to Vitest and does not support ES modules natively.

README

vitest

A blazing fast unit test framework powered by Vite.

This project is currently in closed beta exclusively for Sponsors.
Become a Sponsor of @patak-js or @antfu to access the source code and issues tracker. Learn more at vitest.dev