Extends Chai with assertions for the Sinon.JS mocking framework.

npm install sinon-chai
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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.assertCalledWith(mySpy, "foo");

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


you can say



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)
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)
calledWithExactly spy.should.have.been.calledWithExactly(...args)
alwaysCalledWithExactly spy.should.always.have.been.calledWithExactly(...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.

Installation and Usage


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

var chai = require("chai");
var sinonChai = require("sinon-chai");


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


Sinon–Chai supports being used as an AMD module, registering itself anonymously (just like Chai). So, assuming you have configured your loader to map the Chai and Sinon–Chai files to the respective module IDs "chai" and "sinon-chai", you can use them as follows:

define(function (require, exports, module) {
    var chai = require("chai");
    var sinonChai = require("sinon-chai");


<script> tag

If you include Sinon–Chai directly with a <script> tag, after the one for Chai itself, then it will automatically plug in to Chai and be ready for use. Note that you'll want to get the latest browser build of Sinon.JS as well:

<script src="chai.js"></script>
<script src="sinon-chai.js"></script>
<script src="sinon.js"></script>

Ruby on Rails

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

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