Testing Chrome Storage API wrapper

Question

I am developing Chrome App with AngularJS. As my app uses chrome.storage I wrote wrapper:

angular.module('myApp').factory('chromeStorageApi', function($window){
    if(typeof  $window.chrome.storage == 'undefined')
    return false;

    return{
        set:function(obj, callback){
            $window.chrome.storage.local.set(obj, callback)
            return true;
        },
       .............................
    }
}

I have violated TDD methodology and now I want to test my wrapper. But all my attempts were not successful. I tried to check that, for example, $window.chrome.storage.local.set() has the same arguments as chromeStorageApi.set() but I could not find a way how I can mock $window.chrome.storage.local.

UPDATED:

My last version of Unit test:

describe('chromeStorageApi', function(){

    beforeEach(module('myApp'));

    it('should be able to set data to the storage', inject(function(chromeStorageApi, $window){
        spyOn($window.chrome.storage.local, 'set')
        chromeStorageApi.set({'key':'value'}, function(){ }());
        expect($window.chrome.storage.local.set).toHaveBeenCalled();
        expect($window.chrome.storage.local.set).toHaveBeenCalledWith({'key':'value'}, function(){ }());

    }));
});

But I get an error:

TypeError: 'undefined' is not an object (evaluating '$window.chrome.storage')

Answer 1

I made working tests for me. Here there are:

describe('chromeStorageApi', function(){
    var mockWindow, chromeStorageApi;

    beforeEach(module('myApp'));

    beforeEach(function(){
        mockWindow = {
            chrome:{
                storage:{
                    local: sinon.stub({
                        set: function(){ },
                        get: function(){ },
                        remove: function(){ },
                        clear: function(){ }
                    })
                }
            },
            addEventListener: function(){    }
        }
        module(function($provide){
            $provide.value('$window', mockWindow);
        })
    })

    beforeEach(inject(function(_chromeStorageApi_){
        chromeStorageApi =_chromeStorageApi_;
    }))

    it('should be able to set data to the storage', function(){
        chromeStorageApi.set({'key':'value'}, function(){ }());
        expect(mockWindow.chrome.storage.local.set).toHaveBeenCalled();
        expect(mockWindow.chrome.storage.local.set).toHaveBeenCalledWith({'key':'value'}, function(){ }());

    });

    it('should be able to get data from the storage', function(){
        chromeStorageApi.get('key', function(){ });
        expect(mockWindow.chrome.storage.local.get).toHaveBeenCalled();
        expect(mockWindow.chrome.storage.local.get).toHaveBeenCalledWith('key');
    })
})

I am using sinonJS to create stub with methods. I hope it will be helpful for someone.