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Test your Rails application's JavaScript with the mocha test framework and chai assertion library
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Konacha is a Rails engine that allows you to test your JavaScript with the mocha test framework and chai assertion library.


It is similar to Jasmine and Evergreen, but does not attempt to be framework agnostic. By sticking with Rails, Konacha can take full advantage of features such as the asset pipeline and engines.

Photo credit: FCartegnie, CC-BY-SA.


Add konacha to the :test and :development groups in the Gemfile and bundle install:

group :test, :development do
  gem "konacha"


Create a spec/javascripts directory and name the files in it with a _spec (or _test) suffix. You can write the specs in either JavaScript or CoffeeScript, using a .js or extension respectively, like you would any other script asset.

Require the assets under test and any other dependencies using Sprockets directives. For example, suppose you wanted to test your cool JavaScript Array#sum method, which you placed in app/assets/javascripts/array_sum.js. Write the specs in JavaScript in the file spec/javascripts/array_sum_spec.js:

//= require array_sum

describe("Array#sum", function() {
  it("returns 0 when the Array is empty", function() {

  it("returns the sum of numeric elements", function() {

Or, if you prefer CoffeeScript, in spec/javascripts/

#= require array_sum

describe "Array#sum", ->
  it "returns 0 when the Array is empty", ->

  it "returns the sum of numeric elements", ->

Running (Rake Tasks)

rake konacha:serve

The konacha:serve rake task starts a server for your tests. You can go to the root page to run all specs (e.g. http://localhost:3500/), a sub page to run an individual spec file (e.g. http://localhost:3500/array_sum_spec), or a path to a subdirectory to run a subset of specs (e.g. http://localhost:3500/models).

rake konacha:run

The konacha:run rake task will let you run your tests from the command line.

To run individual specs, pass a comma seperated list of spec file names via the SPEC environment variable.

$ rake konacha:run SPEC=foo_spec
$ rake konacha:run SPEC=foo_spec,bar_spec,etc_spec

Spec Helper

Since Konacha integrates with the asset pipeline, using setup helpers in your specs is easy. Just create a spec_helper.js or file in specs/javascripts and require it in your tests:

//= require spec_helper
//= require array_sum

describe("Array#sum", function() {

Directives and Asset Bundling

We suggest that you explicitly require just the assets necessary for each spec. In CI mode, Konacha will run each spec in isolation, and requiring things explicitly will help ensure your scripts don't accumulate hidden dependencies and tight coupling.

However, you are free to ignore this advice and require the entire application.js asset bundle in your specs or spec helper, or a bundled subset of assets. Requiring bundled assets works like it does in Rails development mode -- Konacha will detect the complete set of dependencies and generate a separate script tag for each one. You won't have to search through a many thousand line application.js bundle to debug a spec failure.


Konacha can be configured in an initializer, e.g. config/initializers/konacha.rb:

Konacha.configure do |config|
  config.spec_dir  = "spec/javascripts"
  config.driver    = :selenium
end if defined?(Konacha)

The defined? check is necessary to avoid a dependency on Konacha in the production environment.

The spec_dir option tells Konacha where to find JavaScript specs. driver names a Capybara driver used for the run task (try :webkit, after installing capybara-webkit).

The values above are the defaults.

Mocha Configuration

You can customize the Mocha options passed into mocha.setup(..) by creating a file named konacha_config.js or in spec/javascripts and setting properties of Konacha.mochaOptions:

// set the Mocha test interface
// see
Konacha.mochaOptions.ui = 'bdd';

// ignore the following globals during leak detection
Konacha.mochaOptions.globals = ['YUI'];

// or, ignore all leaks
Konacha.mochaOptions.ignoreLeaks = true;

// set slow test timeout in ms
Konacha.mochaOptions.timeout = 5;

The ui and reporter Mocha options are set by Konacha and must not be modified.

Test Interface and Assertions

Konacha includes a vendored copy of mocha.js and the chai assertion libraries. By default, it configures Mocha to use the "BDD" test interface, which provides describe(), it(), before(), after(), beforeEach(), and afterEach().

Konacha will make all three of chai's assertion styles available to you: expect, should, and assert. See the chai documentation for the details.

If you use jQuery, you may want to check out chai-jquery for some jQuery-specific assertions. You can add it painlessly with the chai-jquery-rails gem.


One problem often faced when writing unit tests for client side code is that changes to the page are not reverted for the next example, so that successive examples become dependent on each other. Konacha adds a special div to your page with an id of konacha. This div is automatically emptied before each example. You should avoid appending markup to the page body and instead append it to the #konacha div:

describe "transactions", ->
  it "should add stuff in one test...", ->
    $('#konacha').append('<h1 id="added">New Stuff</h1>')
    $('#konacha h1#added').length.should.equal(1)

  it "... should have been removed before the next starts", ->
    $('#konacha h1#added').length.should.equal(0)

Templates / Fixtures

Konacha has no template (a.k.a. HTML fixture) support of its own. Instead, we suggest you use Sprocket's built in support for JavaScript template (.jst) files. Add a spec/javascripts/templates directory, place template files there (using any JS template language supported by Sprockets), require them in your spec or spec_helper, and render them into the #konacha div.

For example, in spec/javascripts/templates/hello.jst.ejs:

<h1>Hello Konacha!</h1>

In spec_helper.js:

//= require_tree ./templates

And your spec:

//= require spec_helper

describe("templating", function() {
  it("is built in to Sprockets", function() {
    $('#konacha h1').text().should.equal('Hello Konacha!');


git clone git://

Run bundle exec rake to run the test suite.

Contributing to Mocha and Chai

The Konacha repository includes the Mocha and Chai repositories as submodules, so you can hack on them directly:

cd mocha # or: cd chai
git checkout master
... hack-hack-hack ...
bundle exec rake assets # make and cp assets based on your changes

Assuming your app's Gemfile points at your Konacha checkout (gem 'konacha', :path => '~/path/to/konacha'), your changes to Mocha and Chai are live in localhost:3500 when you refresh your browser.

You can send pull requests to Mocha and Chai straight out of your submodules.


Copyright (c) 2012 John Firebaugh

MIT License (see the LICENSE file)

Portions: Copyright (c) 2009 Jonas Nicklas, Copyright (c) 20011-2012 TJ Holowaychuk, Copyright (c) 2011 Jake Luer See LICENSE file for details.

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