sinon-chai

What is sinon-chai?

The sinon-chai npm package is an extension for the Chai assertion library that provides a set of custom assertions for Sinon.js spies, stubs, and mocks. It allows for more readable and expressive tests by integrating Sinon.js functionalities directly into Chai's BDD/TDD assertion styles.

What are sinon-chai's main functionalities?

Assert a spy was called

This feature allows you to assert that a Sinon.js spy was called. The code sample demonstrates how to create a spy on a method and then assert that the method was called using Chai's expect syntax.

const sinon = require('sinon');
const chai = require('chai');
const sinonChai = require('sinon-chai');
chai.use(sinonChai);
const expect = chai.expect;

const myObj = {
  myMethod: function() {}
};

const spy = sinon.spy(myObj, 'myMethod');
myObj.myMethod();

expect(spy).to.have.been.called;

Assert a spy was called with specific arguments

This feature allows you to assert that a Sinon.js spy was called with specific arguments. The code sample demonstrates how to create a spy on a method and then assert that the method was called with a specific argument using Chai's expect syntax.

const sinon = require('sinon');
const chai = require('chai');
const sinonChai = require('sinon-chai');
chai.use(sinonChai);
const expect = chai.expect;

const myObj = {
  myMethod: function(arg) {}
};

const spy = sinon.spy(myObj, 'myMethod');
myObj.myMethod('test');

expect(spy).to.have.been.calledWith('test');

Assert a stub was called a specific number of times

This feature allows you to assert that a Sinon.js stub was called a specific number of times. The code sample demonstrates how to create a stub on a method and then assert that the method was called twice using Chai's expect syntax.

const sinon = require('sinon');
const chai = require('chai');
const sinonChai = require('sinon-chai');
chai.use(sinonChai);
const expect = chai.expect;

const myObj = {
  myMethod: function() {}
};

const stub = sinon.stub(myObj, 'myMethod');
myObj.myMethod();
myObj.myMethod();

expect(stub).to.have.been.calledTwice;

Other packages similar to sinon-chai

chai-spies

chai-spies is a plugin for the Chai assertion library that provides a set of custom assertions for spies. It offers similar functionalities to sinon-chai but is focused solely on spies, without the additional features for stubs and mocks that sinon-chai provides.

jest

Jest is a JavaScript testing framework that comes with built-in support for spies, stubs, and mocks. It provides a comprehensive testing solution, including a test runner, assertion library, and mocking capabilities. Unlike sinon-chai, Jest is a standalone framework and does not require additional plugins for spying, stubbing, or mocking.

proxyquire

proxyquire is a module used to mock dependencies in Node.js. It allows you to override dependencies during testing, similar to how Sinon.js stubs work. While it does not integrate directly with Chai like sinon-chai, it provides powerful mocking capabilities that can be used alongside Chai for testing.

README

Sinon.JS Assertions for Chai

Sinon–Chai provides a set of custom assertions for using the Sinon.JS spy, stub, and mocking framework with the Chai assertion library. You get all the benefits of Chai with all the powerful tools of Sinon.JS.

Instead of using Sinon.JS's assertions:

sinon.assert.calledWith(mySpy, "foo");

or awkwardly trying to use Chai's should or expect interfaces on spy properties:

mySpy.calledWith("foo").should.be.ok;
expect(mySpy.calledWith("foo")).to.be.ok;

you can say

mySpy.should.have.been.calledWith("foo");
expect(mySpy).to.have.been.calledWith("foo");

Assertions

All of your favorite Sinon.JS assertions made their way into Sinon–Chai. We show the should syntax here; the expect equivalent is also available.

Sinon.JS property/method	Sinon–Chai assertion
called	spy.should.have.been.called
callCount	spy.should.have.callCount(n)
calledOnce	spy.should.have.been.calledOnce
calledTwice	spy.should.have.been.calledTwice
calledThrice	spy.should.have.been.calledThrice
calledBefore	spy1.should.have.been.calledBefore(spy2)
calledAfter	spy1.should.have.been.calledAfter(spy2)
calledImmediatelyBefore	spy.should.have.been.calledImmediatelyBefore(spy2)
calledImmediatelyAfter	spy.should.have.been.calledImmediatelyAfter(spy2)
calledWithNew	spy.should.have.been.calledWithNew
alwaysCalledWithNew	spy.should.always.have.been.calledWithNew
calledOn	spy.should.have.been.calledOn(context)
alwaysCalledOn	spy.should.always.have.been.calledOn(context)
calledWith	spy.should.have.been.calledWith(...args)
alwaysCalledWith	spy.should.always.have.been.calledWith(...args)
calledOnceWith	spy.should.always.have.been.calledOnceWith(...args)
calledWithExactly	spy.should.have.been.calledWithExactly(...args)
alwaysCalledWithExactly	spy.should.always.have.been.calledWithExactly(...args)
calledOnceWithExactly	spy.should.always.have.been.calledOnceWithExactly(...args)
calledWithMatch	spy.should.have.been.calledWithMatch(...args)
alwaysCalledWithMatch	spy.should.always.have.been.calledWithMatch(...args)
returned	spy.should.have.returned(returnVal)
alwaysReturned	spy.should.have.always.returned(returnVal)
threw	spy.should.have.thrown(errorObjOrErrorTypeStringOrNothing)
alwaysThrew	spy.should.have.always.thrown(errorObjOrErrorTypeStringOrNothing)

For more information on the behavior of each assertion, see the documentation for the corresponding spy methods. These of course work on not only spies, but individual spy calls, stubs, and mocks as well.

Note that you can negate any assertion with Chai's .not. E. g. for notCalled use spy.should.have.not.been.called. Similarly, note that the always methods are accessed with Chai's .always prefix; should.have.been.alwaysCalledWith will not work - instead, use should.always.have.been.calledWith.

For simplicity, this library intentionally only implements Sinon's spy methods, and does not add an interface for Sinon.assert.match. Sinon's matchers are implemented by the samsam library, so if you want a should/expect interface to assert.match you may be interested in chai-samsam, which adds a .deep.match verb that will work with Sinon matchers.

For assert interface there is no need for sinon-chai or chai-samsam. You can install Sinon.JS assertions right into Chai's assert object with expose:

import * as chai from "chai";
import sinon from "sinon";

sinon.assert.expose(chai.assert, { prefix: "" });

Examples

Using Chai's should:

"use strict";
import * as chai from "chai";
import sinon from "sinon";
import sinonChai from "sinon-chai";
chai.should();
chai.use(sinonChai);

function hello(name, cb) {
    cb("hello " + name);
}

describe("hello", function () {
    it("should call callback with correct greeting", function () {
        var cb = sinon.spy();

        hello("foo", cb);

        cb.should.have.been.calledWith("hello foo");
    });
});

Using Chai's expect:

"use strict";
import * as chai from "chai";
import sinon from "sinon";
import sinonChai from "sinon-chai";
const expect = chai.expect;
chai.use(sinonChai);

function hello(name, cb) {
    cb("hello " + name);
}

describe("hello", function () {
    it("should call callback with correct greeting", function () {
        var cb = sinon.spy();

        hello("foo", cb);

        expect(cb).to.have.been.calledWith("hello foo");
    });
});

Installation and Usage

Node

Do an npm install --save-dev sinon-chai to get up and running. Then:

import * as chai from "chai";
import sinonChai from "sinon-chai";

chai.use(sinonChai);

You can of course put this code in a common test fixture file; for an example using Mocha, see the Sinon–Chai tests themselves.

Ruby on Rails

Thanks to Cymen Vig, there's now a Ruby gem of Sinon–Chai that integrates it with the Rails asset pipeline!