Jasmine: BDD for Javascript

In web development, if we are doing web 2.0 and modern web concepts, we have to write a lot of javascript and ajax calls and that will increase client side javascript day by day. We have lot of good javascript libraries for implementation. For faster delivery of features we need to cover the client side javascript with test cases. Jasmine is a tool to do BDD for javascript. It can mock ajax calls and you can use some static templates as a result. Jasmine also can be useful for TDD with javascript.

1. Setting up a project

To set up a project for javascript BDD, first of all you need to add ‘jasmine’ to your gem file. Then after bundle install you will have to run a generator {rails g jasmine:install} to generate jasmine defaults. Now you can run command rake jasmine to see your spec on browser. The server run default on 8888 port. You can see your specs by browsing http://localhost:8888. To write specs you can add a .js file in spec/javascripts/my_javascript_spec.js.

2. Syntax

Jasmine is very similar with rSpec in terms of syntax. It has methods like describe and it. Both functions take two arguments, first a string to show the context and second function to test the results. describe can be used for grouping related specs.

describe('addition', function () {  
    it('adds two numbers', function () {  
        expect(5 + 5).toEqual(10);  

3. Setup and Tear-down

Jasmine provides function beforeEach for setup the spec context and afterEach to clear the context.

describe("Spec setup and tear-down", function() {
  var number;
  beforeEach(function() {
    number = 0;
    number += 1;

  afterEach(function() {
    number = 0;

  it("first assertion", function() {
    expect(number).toEqual(1);              #green

  it("second assertion", function() {
    expect(number).toEqual(1);              #green

4. Matchers

Given few of the matches you can use for assertions –

   expect(["linux", "mac", "windows"]).toContain("linux");  

and a lot many.

5. Custom Matchers

We can write our own custom matcher using this.addMatchers in beforeEach call.

beforeEach(function () {  
    toBeBetween: function (floor, ceiling) {  
      return this.actual > floor && this.actual < ceiling;