Mocha, Should and Sinon

testing_with_mocha.md

http://visionmedia.github.com/mocha/

Mocha is a new library from VisionMedia aka TJ Holowaychuk author of ExpressJs. As usual it has everything you can think of from a testing library and manages to keep it simple and straight forward to use.

Just like jasmine it has a very solid bdd style to testing:

describe 'Widget', ->
  it '#process', ->
    "Hello".should.eql "Hello"

You can also use the should module if you prefer the bdd approach, or if you prefer the tdd approach you can use test and assert.

https://github.com/visionmedia/should.js

To add these testing modules to your project, just include them in your package json as development dependencies:

devDependencies: {
  "mocha": "*"
  ,"should": "*"
  ,"sinon": "*"
}

Then run npm install to pull them down.

npm install

Lets get started

First create a test directory:

mkdir test

Next lets modify package.json to tell npm how to run the tests.

"scripts": {
  "test": "mocha"
}

Now when we get ready to run our tests we simply exec

npm test

This is also ci friendly.

Next we need to define our options in the test directory.

Lets create a file called mocha.opts in the test directy and add the following:

--require should   

--require sinon    

You can also set up any other options that you would like in this file, and each test file will get these options automatically. I had to explicity require sinon but maybe that is just a bug, I will have to check for sure.

Lets write some tests

All you have to do is create either coffee or js files in your test folder and then run npm test and your good to go.

Sinon

Sinon is a Spy/Stub/Mock library that contains a huge amount of patters to test all kinds of stuff. I definately recommend reading the docs at http://sinonjs.org/

How to stub a callback and spy on a result

One of the issues we keep running into is how to stub out call backs from modules that we do not want to test.

example app.coffee

module.exports = ->
  request.get
    uri: 'http://google.com'
    json: true
    (err, resp, body) ->
      console.log resp

spec

app = require '../app'

describe 'app', ->
  it 'request should log 200', ->
    stub = sinon.stub request, 'get'
    spy = sinon.spy console, 'log'
    # stub the callback data we want to return
    stub.yield null, 200, "foo"
    app() # execute 
    # check that console.log was called with an arg of 200
    spy.calledWith(200).should.eql true

Now, this does not test much and the example is silly, but it does make it pretty easy to stub out calls to other methods or modules and provide the data you expect them to return, using the callback system.

--require sinon does not work because you need to access the module's exports. You will need to require it:

var sinon = require('sinon');

See require option at http://visionmedia.github.io/mocha/#usage