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.
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
:
var chai = require("chai");
var sinon = require("sinon");
sinon.assert.expose(chai.assert, { prefix: "" });
Examples
Using Chai's should
:
"use strict";
var chai = require("chai");
var sinon = require("sinon");
var sinonChai = require("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";
var chai = require("chai");
var sinon = require("sinon");
var sinonChai = require("sinon-chai");
var 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:
var chai = require("chai");
var sinonChai = require("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.
AMD
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");
chai.use(sinonChai);
});
<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!