vitest

Vitest is a fast, Vite-native unit testing framework for JavaScript and TypeScript. It is designed to integrate with Vite projects and provide quick feedback by leveraging Vite's module graph and esbuild-based transforms. While inspired by Jest in API and experience, Vitest is built to work seamlessly with Vite's tooling. It supports zero-configuration usage, with optional configuration via a vitest.config.js or vitest.config.ts file for customization.

Vitest offers a familiar test API with functions such as describe and it, along with expectation assertions and lifecycle hooks like beforeEach and afterAll. It exposes a global mocking API under the vi namespace, including vi.fn, vi.spyOn, and vi.mock for module mocking. The framework supports TypeScript, modern ESM, and multiple test environments, including jsdom for browser-like tests and node for server-side tests. Features such as snapshot testing, fake timers, and built-in code coverage reporting are available.

Usage and integration: Vitest integrates tightly with Vite and can run tests in watch mode for fast incremental re-runs as files change. It relies on Vite's configuration system via vite.config.ts and can be extended with a dedicated vitest.config.ts. It is compatible with popular frontend frameworks commonly used with Vite, such as Vue and React, and can execute tests in either browser-like or Node-like environments as needed.

History and licensing: Vitest is an open-source project within the Vite ecosystem, maintained by a community of contributors. It is distributed under an open-source license. The project provides documentation and a growing ecosystem of plugins and reporters, with built-in support for code coverage.