Pablo Villoslada Puigcerber Front-end software engineer who works for Toptal. Passionate about clean code and standards to make things simpler.

Unit testing, as the name implies, is about testing individual units of code.

This post tries to show a few patterns and guidelines to help us with unit testing Angular applications after setting some minimum configuration.

It's aimed at people who are already familiar with Angular but haven't gone deep into unit testing their applications. Although it should also be helpful for completely beginners.

Setting up Angular unit tests

Before we start testing we need to install and configure several dependencies. For this we will be using the package manager npm, although Bower can be used as well.

npm install angular --save bower install angular --save

Note that we can skip to the configuration files section if we don't want to go step by step.

The ngMock module

Angular provides ngMock to inject and mock services into unit tests. And one of the most useful parts of the ngMock module is $httpBackend which lets us mock XHR requests.

npm install angular-mocks --save-dev

Configuring Karma with Jasmine

Karma is a test runner written by the Angular team which allow us to execute tests in multiple browsers.

npm install karma --save-dev

After installing it we need to crete a configuration file running karma init but to extend its functionality we need to install first some plugins.

Testing framework

Angular can be tested using any JavaScript unit testing framework out there, but Jasmine is probably the most popular.

npm install karma-jasmine jasmine-core --save-dev

Browsers

Karma takes care of auto-capturing and killing the browsers, but we need to install at least one of these launchers.

npm install karma-chrome-launcher --save-dev npm install karma-phantomjs-launcher --save-dev npm install karma-firefox-launcher --save-dev npm install karma-safari-launcher --save-dev npm install karma-opera-launcher --save-dev npm install karma-ie-launcher --save-dev

Templates preprocessor

When testing directives we need to set up Karma to serve our templates using a preprocessor to convert HTML into JS string.

ng-html2js creates a "templates" module and put the HTML into the $templateCache .

npm install karma-ng-html2js-preprocessor --save-dev

Code coverage

It's great to identify which parts of our code are lacking test coverage and generate reports with Istanbul, that calculates the percentage of code accessed by tests.

npm install karma karma-coverage --save-dev

Configuration files

package.json

If we haven't followed all the previous steps we must copy the following package.json and run npm install to have all the required dependencies.

{ "name": "unit-testing-angularjs-applications", "version": "1.0.0", "description": "Unit testing AngularJS applications.", "dependencies": { "angular": "^1.3.15" }, "devDependencies": { "angular-mocks": "^1.3.15", "jasmine-core": "^2.3.4", "karma": "^0.12.32", "karma-chrome-launcher": "^0.1.12", "karma-coverage": "^0.3.1", "karma-jasmine": "^0.3.5", "karma-ng-html2js-preprocessor": "^0.1.2" }, "scripts": { "test": "karma start" } }

karma.conf.js

If we haven't generated yet a configuration file now it's the time.

karma init

After answering some questions it will create a karma.conf.js file which we still have to modify including the list of files to load in the browser and configuring the installed preprocessors (ng-html2js and coverage).

The final configuration file should look as follows.

module.exports = function(config) { config.set({ basePath: '', frameworks: ['jasmine'], files: [ 'node_modules/angular/angular.js', 'node_modules/angular-mocks/angular-mocks.js', 'src/**/*.js', 'src/**/*.html' ], exclude: [ ], preprocessors: { 'src/**/*.html': ['ng-html2js'], 'src/**/!(*.mock|*.spec).js': ['coverage'] }, ngHtml2JsPreprocessor: { // strip this from the file path stripPrefix: 'src/', // create a single module that contains templates from all the files moduleName: 'templates' }, reporters: ['progress', 'coverage'], coverageReporter: { type : 'html', // output coverage reports dir : 'coverage/' }, port: 9876, colors: true, logLevel: config.LOG_INFO, autoWatch: true, browsers: ['Chrome'], singleRun: false }); };

And we can run our tests with any of these two commands.

karma start npm test

Mocking external dependencies

To test the functionality of a piece of code in isolation we need to mock any dependency.

Angular is written with testability in mind and come with dependency injection built in, what help us to achieve decoupling and therefore to test our objects in isolation.

A service (service, factory, value, constant, or provider) is the most common type of dependency in Angular applications and they are defined via providers.

The Angular injector retrieves object instances as defined by providers.

So there are at least two ways we can mock our services:

Using the $provide service

We can provide our own implementation in a beforeEach Jasmine block, creating an object with the same methods as the original service.

var myService; beforeEach(module(function($provide) { myService = { syncCall: function() {}, asyncCall: function() {} }; $provide.value('myService', myService); }));

Creating a reusable service provider

Or we can reuse it creating the implementation in a separate my-service.mock.js file using the provider syntax.

angular.module('myServiceMock', []) .provider('myService', function() { this.$get = function() { return { syncCall: function() {}, asyncCall: function() {} }; }; });

And later we load the mocked module in a beforeEach Jasmine block inside of our test suite.

beforeEach(module('myServiceMock')); var myService; beforeEach(inject(function(_myService_) { myService = _myService_; }));

In any case it's good to load the mocked modules after the module we are testing to be sure the mock overrides the actual implementation.

Testing patterns

As code and specs are better placed side-by-side we can put all our files inside the src folder, using the .spec.js suffix to differentiate test files.

src/my-controller.js src/my-controller.spec.js src/my-directive.js src/my-directive.spec.js src/my-service.js src/my-service.spec.js

An we can make testing simpler if we follow the same pattern to test each of our objects:

Describe the object with type and name. Load our object's module. Load mock modules as needed. Inject dependencies and spy on methods. Initialize the object: Services just need to get injected. Controllers are instantiated using the $controller service. We need to $compile directives. Write expectations grouped in describe blocks.

Therefore all our test files will have the same structure with the common content in beforeEach blocks that run before every test. And nested describe blocks containing the self-describing expectations inside of it blocks.

describe('ObjectType: objectName', function() { beforeEach(module('objectModule')); var myObject; beforeEach(inject(function(_myObject_) { myObject = _myObject_; })); describe('Method: methodName', function() { it('should do ...', function() { expect(true).toBe(true); }); }); });

Controllers

Controllers are easy to test as long as we don't manipulate the DOM and functions have a single and clear purpose.

We should test for the state, synchronous and asynchronous calls to services, and events.

Code

We create our basic controller using the controller as syntax. And we inject the dependencies on a external service and the $scope for using events.

angular.module('myControllerModule', ['myServiceModule']) .controller('MyController', ['$scope', 'myService', MyController]); function MyController($scope, myService) { var vm = this; }

Then we expose a method and different types of properties to the view.

vm.hasError = false; vm.myProperty = 'My Controller'; vm.myArray = []; vm.myObject = myService.syncCall(); vm.myNumber = 0; vm.changeProperty = changeProperty; function changeProperty(value) { vm.myProperty = value; }

We call the service asynchronously setting the success and error handlers.

myService.asyncCall().then( function(data) { vm.myArray = data; }, function() { vm.hasError = true; } );

And finally we use the $scope to handle events.

$scope.$emit('my-event'); $scope.$on('some-event', function() { vm.myNumber++; });

Having thus this code.

angular.module('myControllerModule', ['myServiceModule']) .controller('MyController', ['$scope', 'myService', MyController]); function MyController($scope, myService) { var vm = this; vm.hasError = false; vm.myProperty = 'My Controller'; vm.myArray = []; vm.myObject = myService.syncCall(); vm.myNumber = 0; vm.changeProperty = changeProperty; myService.asyncCall().then( function(data) { vm.myArray = data; }, function() { vm.hasError = true; } ); function changeProperty(value) { vm.myProperty = value; } $scope.$emit('my-event'); $scope.$on('some-event', function() { vm.myNumber++; }); }

Specs

We write the essential structure of the test suite loading the mocked service after the controller's module.

describe('Controller: MyController', function() { beforeEach(module('myControllerModule')); beforeEach(module('myServiceMock')); });

For testing calls to other services we need to spy their methods. And Jasmine provides us with the spyOn function to track calls and arguments passed.

With callThrough() we delegate to the actual implementation. However for the asynchronous method we need to mock its behaviour returning a promise provided by the $q service.

var myService; var deferred; // Mock services and spy on methods beforeEach(inject(function($q, _myService_) { deferred = $q.defer(); myService = _myService_; spyOn(myService, 'syncCall').and.callThrough(); spyOn(myService, 'asyncCall').and.returnValue(deferred.promise); }));

To keep it dry we initialize the controller passing the mocked dependencies in a different beforeEach block.

var MyController; var scope; // Initialize the controller and a mock scope. beforeEach(inject(function($rootScope, $controller) { scope = $rootScope.$new(); spyOn(scope, '$emit'); MyController = $controller('MyController', { $scope: scope, myService: myService }); }));

And we start testing the state of our controller. As we use the controller as syntax we don't need to test for the $scope but directly for the exposed properties and methods of the controller.

describe('State', function() { it('should expose myProperty to the view', function() { expect(MyController.myProperty).toBeDefined(); // We can use Angular helpers. expect(angular.isArray(MyController.myArray)).toBe(true); expect(angular.isObject(MyController.myObject)).toBe(true); expect(angular.isNumber(MyController.myNumber)).toBe(true); }); it('should expose a method to change myProperty', function() { expect(MyController.changeProperty).toBeDefined(); expect(angular.isFunction(MyController.changeProperty)).toBe(true); }); });

For testing the actual behaviour of a method we need to fire it with different arguments.

it('should change myProperty', function() { MyController.changeProperty(true); expect(MyController.myProperty).toBe(true); MyController.changeProperty(false); expect(MyController.myProperty).toBe(false); });

While testing calls to services it's straight forward using Jasmine spies.

describe('Synchronous calls', function() { it('should call syncCall on myService', function() { expect(myService.syncCall).toHaveBeenCalled(); expect(myService.syncCall.calls.count()).toBe(1); }); }); describe('Asynchronous calls', function() { it('should call asyncCall on myService', function() { expect(myService.asyncCall).toHaveBeenCalled(); expect(myService.asyncCall.calls.count()).toBe(1); }); });

In adittion, we need to test promise resolution for asynchronous methods.

When setting the test suite we have made the asynchronous call to return a promise, that we can now resolve or reject as our convenience to test success and error.

it('should do something on success', function() { var data = ['something', 'on', 'success']; deferred.resolve(data); // Resolve the promise. scope.$digest(); // Check for state on success. expect(MyController.myArray).toBe(data); }); it('should do something on error', function() { deferred.reject(400); // Reject the promise. scope.$digest(); // Check for state on error. expect(MyController.hasError).toBe(true); });

And with the controller as syntax the only place where we need to test the $scope it's when we emit or listen for events.

describe('Events', function() { it('should emit an event', function() { expect(scope.$emit).toHaveBeenCalledWith('my-event'); expect(scope.$emit.calls.count()).toBe(1); }); it('should do something when some-event is caught', inject(function($rootScope) { $rootScope.$broadcast('some-event'); // Check for state after event is caught. expect(MyController.myNumber).toBe(1); })); });

Services

Services are even easier to test than controllers.

In addition of testing calls to other services, we should test for the output of our methods and HTTP requests.

But as we don't want to send XHR requests to a real server we use $httpBackend.

Code

We lay out a simple service with a synchronous method that calculates the factorial and one asynchronous that uses the native $http service to query an external API for data.

angular.module('myServiceModule', []) .service('myService', MyService); function MyService($http, $q) { var f = []; this.factorial = factorial; this.getThings = getThings; function factorial(n) { if (n === 0 || n === 1) { return 1; } if (f[n] > 0) { return f[n]; } f[n] = factorial(n-1) * n; return f[n]; } }

Note that if we return a non-promised value from the error callback it will resolve and not reject the derived promise. So we need to reject it explicitly.

function getThings() { return $http.get('/api/things').then( function(response) { return response.data; }, function(error) { return $q.reject(error.status); } ); }

Specs

Setting the test we need to get hold of the $httpBackend to mock the calls to the API and test for the expected results.

describe('Service: myService', function() { beforeEach(module('myServiceModule')); var myService; var httpBackend; beforeEach(inject(function($httpBackend, _myService_) { httpBackend = $httpBackend; myService = _myService_; })); });

For testing synchronous methods we just need to check that their output is the one we are expecting.

describe('Output of methods', function() { it('should return the product of all positive integers less than or equal to n', function() { expect(myService.factorial(0)).toBe(1); expect(myService.factorial(5)).toBe(120); expect(myService.factorial(10)).toBe(3628800); }); });

But the fun starts when we test our asynchronous methods.

For our tests to run quickly we use the mocked $httpBackend implementation to respond with data to our calls hence avoiding expensive requests to a real server.

As requests are treated asynchronously we need to flush them and that's the reason why we add an afterEach block to verify there is nothing pending at the end of the tests.

Testing that our backend is being called we just need to create expectations with the address of our API endpoint.

describe('HTTP calls', function() { afterEach(function() { httpBackend.verifyNoOutstandingExpectation(); httpBackend.verifyNoOutstandingRequest(); }); it('should call the API', function() { httpBackend.expectGET(/\/api\/things/).respond(''); myService.getThings(); httpBackend.flush(); }); });

Though testing the returned values it's more complicated to set.

First we need to spy upon an object with success and error handlers that will be passed to the method call.

var myThings; var errorStatus; = ''; var handler; beforeEach(function() { myThings = []; errorStatus = ''; handler = { success: function(data) { myThings = data; }, error: function(data) { errorStatus = data; } }; spyOn(handler, 'success').and.callThrough(); spyOn(handler, 'error').and.callThrough(); });

And after we need to create a backend definition with the response to test the handler has been called with the expected values.

it('should return an array of things on success', function() { var response = ['one thing', 'another thing']; httpBackend.whenGET(/\/api\/things/).respond(response); myService.getThings().then(handler.success, handler.error); httpBackend.flush(); expect(handler.success).toHaveBeenCalled(); expect(myThings).toEqual(response); expect(handler.error).not.toHaveBeenCalled(); expect(errorStatus).toEqual(''); });

If we need to simulate an error we have to pass a numeric value bigger than 300 as the first parameter of the response.

it('should return the status on error', function() { httpBackend.whenGET(/\/api\/things/).respond(404, {status: 404}); myService.getThings().then(handler.success, handler.error); httpBackend.flush(); expect(handler.error).toHaveBeenCalled(); expect(errorStatus).toEqual(404); expect(handler.success).not.toHaveBeenCalled(); expect(myThings).toEqual([]); });

Directives

Directives are a bit more complex to test as we need to $compile them manually to test the compiled DOM.

Additionally we use angular.element and the provided jQuery or jqLite methods to manipulate the DOM.

Code

We create a directive with an isolated scope and its own controller using the controller as syntax.

angular.module('myDirectiveModule', []) .directive('myDirective', function() { return { bindToController: true, controller: function() { var vm = this; vm.doSomething = doSomething; function doSomething() { vm.something.name = 'Do something'; } }, controllerAs: 'vm', restrict: 'E', scope: { something: '=' }, templateUrl: 'my-directive.html' }; });

And we use an external template to see ng-html2js in action.

<h1 ng-click="vm.doSomething()">{{vm.something.name}}</h1>

Specs

To test it we need to load the directive's module but also the one holding all the templates that we have configured before with the ng-html2js preprocessor.

Next we $compile the directive and to apply the desired scope we need to trigger the $digest loop.

describe('Directive: myDirective', function() { beforeEach(module('myDirectiveModule')); beforeEach(module('templates')); var element; var scope; beforeEach(inject(function($rootScope, $compile) { scope = $rootScope.$new(); element = angular.element('<my-directive something="thing"></my-directive>'); element = $compile(element)(scope); scope.thing = {name: 'My thing'}; scope.$digest(); })); });

Using the jQuery/jqLite methods we can check for what have been rendered.

it('should render something', function() { var h1 = element.find('h1'); expect(h1.text()).toBe('My thing'); });

And when the scope changes we should check if the rendered DOM has been updated with the new values.

it('should update the rendered text when scope changes', function() { scope.thing.name = 'My new thing'; scope.$digest(); var h1 = element.find('h1'); expect(h1.text()).toBe('My new thing'); });

If is needed we can test the directive controller grabbing an instance of it, passing the name of the directive to the element.controller() .

describe('Directive controller', function() { var controller; beforeEach(function() { controller = element.controller('myDirective'); }); it('should do something', function() { expect(controller.doSomething).toBeDefined(); controller.doSomething(); expect(controller.something.name).toBe('Do something'); }); });

Providers

Providers are the toughest to test as we need to intercept them before they are injected.

But once we have solved that step we can test them as any other service.

Code

Our Hello World provider can be configured to say "hello" to anything.

angular.module('myProviderModule') .provider('helloWorld', helloWorld); function helloWorld() { var name; return { configure: function(value) { name = value; }, $get: function() { return { sayHello: function() { return 'Hello ' + name; } }; } }; }

Specs

We intercept the provider when we load the module before triggering the injection.

describe('Provider: helloWorld', function() { var helloWorldProvider; beforeEach(function() { module('myProviderModule', function(_helloWorldProvider_) { helloWorldProvider = _helloWorldProvider_; }); }); var helloWorld; beforeEach(inject(function(_helloWorld_) { helloWorld = _helloWorld_; })); });

And then we can test both instances as we would do with any other service.

it('should do something', function() { expect(!!helloWorldProvider).toBe(true); }); describe('Service method', function() { beforeEach(function() { helloWorldProvider.configure('World'); }); it('should say hello world', function() { expect(helloWorld.sayHello()).toBe('Hello World'); }); });

Conclusion and next steps

Although unit testing might seem scary at the beginning, once we master some of these patterns it's going to be a breeze to test our applications, making us feel more confident with the code we are developing.

But this is just the tip of the iceberg as unit testing help us to test isolated pieces of code. To check if all these pieces work well when integrated together we need to do end to end testing (e2e) and for it we have to use the Protractor framework, built by the Angular team.