Over a million developers have joined DZone.

Jasmine - An Introduction

· Web Dev Zone

This page is the result of taking notes from the session about Jasmine by Davis W. Frank at this years Fluent Conference in San Francisco. Unfortunately I wasn’t there, but O’Reilly was so kind to give me access to the amazing video compilation of the sessions.

Intro

All the code samples of the talk are available in this Gist here. I’ve written them down here as well, so you might simply proceed to get through them.

Why to test?

Personally, I think this question shouldn’t be made any more nowadays, but still, that’s what Davis W. Frank mentioned in his talk:

  • fix “broken windows”
  • extract common behavior (without fear of breaking something)
  • swap dependencies
  • refactor as you need

Fear not! I am using Jasmine to refactor JavaScript safely
(by an unknown Twitter user)

Here are some useful links to get started:

A first Jasmine Test: BallSpec.js

A first example of a Jasmine test:

describe("Ball", function () {
    var ball;

    before(function() {
        ball = new Ball();
    });

    it("should start deflated", function() {
        expect(ball.isFull()).toEqual(false);
    });
});

The according Ball.js´ looks like this

function Ball() {
  var self = this;

  var full = false;

  self.inflate = function() {
    full = true;
  };

  self.isFull = function() {
    return full;
  };

  return self;
}

Matchers

Jasmine has the following “matchers”:

  • toBe()
  • toBeTruthy()
  • toBeDefined()
  • toMatch()
  • toContain()
  • toBeCloseTo()
  • toThrow() - …

Spies

..it also has Spies which is how they do test doubles in Jasmine, basically thy include mocks, stubs, fakes or doubles.

Here’s an example of spying on something

describe("Game", function() {
    var game, ball;

    beforeEach(function(){
        ball = new Ball();
        spyOn(ball, "inflate").andCallThrough();
        game = new Game();
    });

});

The describes can even be nested (infinitely), so for instance

describe("Game", function(){
    ...
    describe("with a not-full ball", function(){
        beforeEach(function(){
            game.prepare(ball);
        });

        it("should inflate before play", function(){
            expect(ball.inflate).toHaveBeenCalled();
        });
    });
});

expect(ball.inflate).toHaveBeenCalled(); here verifies that the inflate function has actually been called. This is possible because before we added a spy on the inflate function, remember:

spyOn(ball, "inflate").andCallThrough();

The Game.js itself looks like

function Game() {
    this.prepare = function(ball){
        if(ball.isFull()){
            return;
        }

        ball.inflate();
    }
}

The Mock Clock

This mechanism is used to test calls to setTimeout() or setInterval(). Jasmine basically overwrites these functions and makes them synchronous s.t. they don’t tick until (in the test) one explicitly gives them the command to do so.

For example:

describe("Manually ticking the Jasmine Mock Clock", function() {
  var timerCallback;

  beforeEach(function() {
    timerCallback = jasmine.createSpy('timerCallback');
    jasmine.Clock.useMock();
  });

  it("causes a timeout to be called synchronously", function() {
    setTimeout(function() {
      timerCallback();
    }, 100);

    expect(timerCallback).not.toHaveBeenCalled();
    jasmine.Clock.tick(101);
    expect(timerCallback).toHaveBeenCalled();
  });
});

Note the creation of the timer “mock” in the beforeEach and then the explicit command jasmine.Clock.tick(101) to tell the timers to tick.

Note also the line expect(timerCallback).not.toHaveBeenCalled(). Inside a chaining every expectation can be negated by adding the .not. in the chain.

Jasmine Ajax

This is not part of the Jasmine core but is available on GitHub. It does a similar thing as the “Mock Clock” does with timers, just that it applies to ajax calls. It stubs the default xhr object to avoid making real ajax calls as that’s not what we want when running automated (unit) tests.

For example:

describe("When using the Jasmine Ajax Mock", function() {
  var onSuccess, onComplete, onFailure, request;

  beforeEach(function() {
    onSuccess = jasmine.createSpy('onSuccess');
    onComplete = jasmine.createSpy('onComplete');
    onFailure = jasmine.createSpy('onFailure');
    
    jasmine.Ajax.useMock();

    jQuery.ajax({
      url:      "example.com/someApi",
      success:  onSuccess,
      complete: onComplete,
      error:    onFailure
    });
    request = mostRecentAjaxRequest();
  });

  it("prevents the call from leaving your system", function() {
    expect(request.url).toEqual("http://example.com/someApi");    
  });

});

It is also possible to assert on a (here) successful response..

describe("When using the Jasmine Ajax Mock", function() {
  var onSuccess, onComplete, onFailure, request;
  
  ...

  describe("with a successful response", function() {
    beforeEach(function() {
      var successResponse = {
        status: 200,
        responseText: "w00t!"
      };      
      request.response(successResponse);
    });

    it("should call the success callback", function() {
      expect(onSuccess).toHaveBeenCalledWith("w00t!");
    });

    it("should call the complete callback", function() {
      expect(onComplete).toHaveBeenCalled();
    });
  });

});

..or a failed response

describe("When using the Jasmine Ajax Mock", function() {
  var onSuccess, onComplete, onFailure, request;
  
  ...

  describe("with a successful response", function() {
    beforeEach(function() {
      var failureResponse = {
        status: 500,
        responseText: "Doh!"
      };      
      request.response(failureResponse);
    });

    it("should call the failure callback", function() {
      expect(onFailure).toHaveBeenCalledWith("Doh!");
    });

    it("should call the complete callback", function() {
      expect(onComplete).toHaveBeenCalled();
    });
  })  

});

It is important to understand that the ajax call is mocked out at the very last possible moment, therefore the response here that is is “stubbed” looks nearly like the one a server would send back down to the client.

var failureResponse = {
    status: 500,
    responseText: "Doh!"
}; 

Async

For ajax and the timeout functions the mocks should be used. Asyncs may be useful for dealing with nodejs for instance.

Q&A

Recommendations to test multiple browsers

Selenium web drivers might be an option, basically to run the tests and then to extract the results from the DOM.

How do you organize your files?

Dependent on project. Normally the tests folder tree structure should reflect the one of the source files. This is usually comfortable for easily finding the according source file and vice versa.

 

 

 

 

 

 

 

 

 

 

 

 

Topics:

Published at DZone with permission of Juri Strumpflohner, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

SEE AN EXAMPLE
Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.
Subscribe

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}