sinon

What is sinon?

Sinon is a testing utility that provides functions for spies, stubs, and mocks, which are essential for behavior-driven development and testing in JavaScript. It works with any unit testing framework and is widely used for its versatile API and comprehensive feature set.

What are sinon's main functionalities?

Spies

Spies are functions that record their usage, such as how many times they were called, with what arguments, and what was returned. They can be used to wrap existing functions to add this tracking ability.

const sinon = require('sinon');
const myFunction = sinon.spy();
myFunction('Hello', 'World');
console.log(myFunction.calledOnce); // true

Stubs

Stubs are like spies, but they can replace the target function's behavior, either by returning a specific value or by throwing an exception. They are useful for controlling a function's behavior in a test.

const sinon = require('sinon');
const myObj = { myMethod: () => 'original' };
const stub = sinon.stub(myObj, 'myMethod').returns('stubbed');
console.log(myObj.myMethod()); // 'stubbed'

Mocks

Mocks are fake methods (like stubs) with pre-programmed behavior and expectations. They are used to assert that certain methods are called in certain ways.

const sinon = require('sinon');
const myObj = { myMethod: () => 'original' };
const mock = sinon.mock(myObj);
mock.expects('myMethod').once().returns('mocked');
console.log(myObj.myMethod()); // 'mocked'
mock.verify();

Other packages similar to sinon

jest

Jest is a complete testing framework that comes with spies, mocks, and stubs built-in. It is often compared to Sinon for its mocking capabilities, but Jest provides a more integrated experience with a test runner and assertion library included.

testdouble

Testdouble.js (npm package 'testdouble') is a minimalistic testing library that provides a similar API to Sinon for creating test doubles like stubs, mocks, and spies. It focuses on providing a more user-friendly experience with better error messages and simpler APIs.

chai-spies

Chai-spies is a plugin for the Chai assertion library that adds spy capabilities. While it doesn't offer as comprehensive a set of features as Sinon, it integrates well with Chai for developers who prefer that assertion style.

README

Sinon.JS

Standalone and test framework agnostic JavaScript test spies, stubs and mocks (pronounced "sigh-non", named after Sinon, the warrior).

Compatibility

For details on compatibility and browser support, please see COMPATIBILITY.md

Installation

via npm

$ npm install sinon

or via Sinon's browser builds available for download on the homepage. There are also npm based CDNs one can use.

Usage

See the sinon project homepage for documentation on usage.

If you have questions that are not covered by the documentation, you can check out the sinon tag on Stack Overflow.

Goals

• No global pollution
• Easy to use
• Require minimal “integration”
• Easy to embed seamlessly with any testing framework
• Easily fake any interface
• Ship with ready-to-use fakes for timers

Contribute?

See CONTRIBUTING.md for details on how you can contribute to Sinon.JS

Backers

Thank you to all our backers! 🙏 [Become a backer]

Sponsors

Become a sponsor and get your logo on our README on GitHub with a link to your site. [Become a sponsor]

Licence

Sinon.js was released under BSD-3

Changelog

21.0.0

• fd10f13f chore!: remove assert.failException property (#2659) (Morgan Roderick)

  This was used for allowing customisation of the thrown error between sandboxes and for customisation for integrations (most likely from the days of BusterJS).

  To my knowledge and what I've been able to find on GitHub, this has never had any production use by end users.

  BREAKING CHANGE: this removes assert.failException from the API

Released by Morgan Roderick on 2025-06-13.