sinon

Sinon.JS is a popular JavaScript testing library that provides a comprehensive set of tools for writing unit tests. The library offers three core concepts: spies, stubs, and mocks. Spies wrap functions to record calls and arguments, stubs replace functions with controlled behavior, and mocks combine both to verify expected behavior. The library is designed to be standalone and test framework agnostic, meaning it can be used with any testing framework such as Mocha, Jasmine, QUnit, or Jest. It aims for no global pollution, ease of use, minimal integration requirements, and seamless embedding with any testing framework. Installation is straightforward via npm (`npm install sinon`) or through browser builds available on the project homepage. The library also supports npm-based CDNs for easy integration. Key features include: - Spies: Record function calls, arguments, and return values - Stubs: Replace functions with controlled behavior - Mocks: Combine spies and stubs to verify expected behavior - Fake timers: Ready-to-use fakes for setTimeout, setInterval, Date, etc. - No global pollution: Clean API that doesn't pollute the global namespace The project follows a BSD-3 license and is actively maintained with contributions from the community. It uses artifact-first contract tests to protect public APIs during migration. The `lib/` directory contains generated build output and is not committed to the repository; developers can regenerate it locally using `npm run build`. Sinon.JS is widely used in the JavaScript ecosystem for writing reliable, maintainable unit tests. Its clean API and framework-agnostic design make it a versatile choice for developers working across different testing environments.