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 .js.coffee 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/array_sum_spec.js.coffee:

#= require array_sum

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

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

Your tests are run inside an iframe. You have the entire <body> element to yourself, and it is automatically reset between tests.

Running (Rake Tasks)

In the Browser

To start a server for your tests, type:

$ bundle exec rake konacha:serve

Then open http://localhost:3500 in your browser, and you will see all your tests running. You can also go to 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).

This is the recommended mode for development, since you can simply hit refresh to reload all your test and asset files. To debug tests, use the debugger statement anywhere in a test to halt execution.

To run code in the JavaScript console, be sure to select the desired iframe first, so your code runs in the correct context.

Selecting the test-context frame in Chrome

Command-Line Runner

To run your tests from the command line, type:

$ bundle exec rake konacha:run

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

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

Konacha includes a default formatter modeled upon RSpec's ProgressFormatter. Additionally, Konacha's runner implements the same protocol as RSpec, so many RSpec formatters also work with Konacha.

To specify one or more formatters, provide a comma separated list of class names in the FORMAT environment variable. For example, you can run both Ruby and JavaScript specs with CI integration using ci_reporter:

$ bundle exec rake ci:setup:rspec spec konacha:run FORMAT=CI::Reporter::RSpec

You will need to require any formatters you use. It's a good idea to do this within a defined? check in your Konacha initializer.

To automatically trigger reruns when files change, try guard-konacha.

Spec Helper

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

//= require spec_helper
//= require array_sum

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

The spec_helper is a good place to set Mocha and Chai options as well, for instance:

// set the Mocha test interface
// see http://visionmedia.github.com/mocha/#interfaces

// ignore the following globals during leak detection

// or, ignore all leaks

// set slow test timeout in ms

// Show stack trace on failing assertion.
chai.Assertion.includeStack = true;

Directives and Asset Bundling

We suggest that you explicitly require just the assets necessary for each spec. Konacha runs each spec file 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.spec_matcher = /_spec\.|_test\./
  config.driver       = :selenium
  config.stylesheets  = %w(application)
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. spec_matcher is an object responding to === (most likely a Regexp); it receives a filename and should return true if the file is a spec. driver names a Capybara driver used for the run task (try :poltergeist, after installing PhantomJS). The stylesheets option sets the stylesheets to be linked from the <head> of the test runner iframe.

The values above are the defaults.

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. There are a lot of interesting chai matchers out there, see the chai plugins page

To make all these available for your konacha environment, see the Konacha-chai-matchers gem

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 <body>.

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() {
    $('body h1').text().should.equal('Hello Konacha!');

Upgrading from Konacha 1.x


As of Konacha 2.0, each test file is run inside an isolated iframe. For compatibility with Konacha 1.x, the iframe's <body> element will have id="konacha" set on it.

Previously, all test files would run in the same environment. Thus, if only one test file pulled in an external library, all tests would be able to use it. Now test files are run in isolation. If you encounter an undefined JavaScript module in your test, you may be missing an explicit //= require call somewhere.


In Konacha 1.x you would set Konacha.mochaOptions in konacha_config.js:

// Old syntax
Konacha.mochaOptions.ignoreLeaks = true;

The konacha_config.js file is no longer used by Konacha 2.0. Instead, call Mocha's own methods in spec_helper.js:

// New syntax

Global mocha

Konacha 2.0 ships with an upgraded Mocha. Some objects that were previously available on the global mocha object might now be located on Mocha. If you get an error message to this effect, adjust your code accordingly.


git clone git://github.com/jfirebaugh/konacha.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 tj@vision-media.ca, Copyright (c) 2011 Jake Luer jake@alogicalparadox.com. See LICENSE file for details.