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AngularJS Unit Testing – For Real, Though

Introduction

When it comes to contemporary web development, AngularJS is the new hotness. Its unique approach to HTML compilation and two-way data binding make it an effective tool for efficiently building client-side web apps. When I found out that Quick Left would be using it to build a production application for one of our clients, I was excited to learn as much about it as I could. I scoured the interwebs for every tutorial and walkthrough to be found on the Google Machine. They were really helpful in understanding directives, template compilation, and the event loop, but when it came to testing, I found that the topic was often hand-waved.

I was trained to practice Test-Driven Development, and I feel like something’s out of place whenever I’m out of the “Red-Green-Refactor” flow. Since we were still learning the ropes for effective testing in Angular, the team sometimes had to rely on ‘test-after’ development. This started to make me feel itchy, so I decided to focus on figuring out testing. I sprinted on it for a week, and we soon went from about 40% test coverage
to 86% (By the way, if you haven’t tried it yet, check out Istabul for checking out your test coverage in JS apps).

Today I’d like to share some things I learned along the way. As good as the Angular docs are, testing a production app is rarely as simple as the examples you’ll find there. There are a lot of gotchas that pop
up along the way, and I had to struggle my way through figuring out how to make things work. I found several workarounds that came in handy time and time again. In this article, we’re going to look at some of them:

  1. Reusable End-to-End (e2e) pages
  2. Dealing with functions that return a promise
  3. Mocking controller and directive dependencies
  4. Accessing child and isolate scopes

This article is written for intermediate to advanced developers using AngularJS to build production applications, who would like to reduce some of the pain of testing. It is my hope that feeling secure in testing workflow will enable the reader to practice a TDD workflow and build a more solid app.

Test Tools

There are many test frameworks and tools available to the Angular developer, and you may already have preferences around tooling. Here’s the setup that we chose, and we’ll be using for the rest of this article:

  • Karma: The official AngularJS team test runner. We’ll use it to launch
    Chrome, Firefox, and PhantomJS.

  • AngularMocks: Provides support for injecting and mocking Angular services in
    unit tests.

  • Protractor: The feature testing tool for AngularJS, which launches
    your app in a browser and interacts with it via Selenium.

  • Mocha: A node.js based test framework. Gives us the ability to write describe blocks and make assertions.

  • Chai: Assertion library that hooks into Mocha, and gives us access to Behavior-Driven Development assertions like expect, should, and assert. In this example, we’ll be using expect.

  • Chai-as-promised: This Chai plugin is really helpful for dealing with function calls that return a promise. It gives us the ability to say things like: expect(foo).to.be.fulfilled, or expect(foo).to.eventually.equal(bar).

  • Sinon: Stubbing and mocking library. We’ll use it to mock out directive and controller dependencies in unit tests, and to check that functions are being called with the correct arguments.

  • Browserify: Allows us to easily require modules of code between files in the project.

  • Partialify: Allows us to require HTML templates inline in our AngularJS directives.

  • Lodash: Utilities used to extend JavaScript and make it easier to work with.

Setting Up A Test Helper

We’ll start by creating a test helper that will load in the necessary dependencies. Here, I’m pulling in Angular Mocks, Chai, Chai-as-promised, and Sinon.

// test/test-helper.js

// Load in our actual project
require('widgetProject');

// Dependencies
require('angular-mocks');
var chai = require('chai');
chai.use('sinon-chai');
chai.use('chai-as-promised');

var sinon = require('sinon');

beforeEach(function() {
  // Create a new sandbox before each test
  this.sinon = sinon.sandbox.create();
});

afterEach(function() {
  // Cleanup the sandbox to remove all the stubs
  this.sinon.restore();
});

module.exports = {
  rootUrl: 'http://localhost:9000',
  expect: chai.expect
}

Getting Started: Top-Down Testing

I’m a big proponent of a top-down testing style. Starting with a feature that I know I want to build, I like to write a pseudo-gherkin scenario describing the desired behavior and translate it into a feature test. I run
that test and let it fail. Then I can begin building all the parts of the system that I need to make the feature work, using unit tests to guide me along the way.

For these demos, I’ll building an imaginary application called “Widgets”, that can display a list of widgets, create new widgets, and edit existing widgets. The code you’ll see here is not enough to build the complete application, just enough to help the test examples make sense. We’ll start by writing an e2e test describing the workflow for creating a new widget.

To start things off, I’ll describe a pattern we found useful in e2e testing: creating a reusable “page” file. For this example, we’ll imagine that we’re working on a form to create a new widget.

Reusable e2e Test Pages

When working on a one-page app, it makes sense to DRY up the feature tests by writing a reusable “page” that you can reference from within multiple e2e tests.

There are many ways to structure the tests in an Angular project. Today, we’ll go with this setup:

widgets-project
|-test
|  |
|  |-e2e
|  |  |-pages
|  |
|  |-unit

Inside of the pages folder, we’ll create a WidgetsPage function that we can require into our e2e tests. It has five references:

  • widgetRepeater: a list of widgets contained in an ng-repeat
  • firstWidget: the first widget in the repeater
  • widgetCreateForm: the form used to create a widget
  • widgetCreateNameField: form field to enter the widget’s name
  • widgetCreateSubmit: form submit button

In the end, it looks like this:

// test/e2e/pages/widgets-page.js

var helpers = require('../../test-helper');

function WidgetsPage() {
  this.get = function() {
    browser.get(helpers.rootUrl + '/widgets');
  }

  this.widgetRepeater = by.repeater('widget in widgets');
  this.firstWidget = element(this.widgetRepeater.row(0));

  this.widgetCreateForm = element(by.css('.widget-create-form'));
  this.widgetCreateNameField = this.widgetCreateForm.element(by.model('widget.name');
  this.widgetCreateSubmit = this.widgetCreateForm.element(by.buttonText('Create');
}

module.exports = WidgetsPage

From within my e2e tests, I can now load up this page and interact with the elements on it. Here’s how I would use the test page in a test for the widget create form:

// e2e/widgets_test.js

var helpers = require('../test-helper');
var expect = helpers.expect;
var WidgetsPage = require('./pages/widgets-page');

describe('creating widgets', function() {
  beforeEach(function() {
    this.page = new WidgetsPage();
    this.page.get();
  });

  it('should create a new widget', function() {
    expect(this.page.firstWidget).to.be.undefined;
    expect(this.page.widgetCreateForm.isDisplayed()).to.eventually.be.true;
    this.page.widgetCreateNameField.sendKeys('New Widget');
    this.page.widgetCreateSubmit.click();
    expect(this.page.firstWidget.getText()).to.eventually.equal('Name: New Widget');
  });
});

Let’s step through what’s happening here. First, we load up the test helpers and get expect and the reusable WidgetsPage from them. In the beforeEach, we load up the page in the browser. Then, in the example, we use the page elements we defined in the WidgetsPage to interact with the page. We check that there are no widgets, then fill out the form to create one named “New Widget”, and check that it is displayed on the page.

By splitting the logic for the form out into a reusable “page”, we can now reuse it to test form validations or custom form directives later on.

Dealing With Functions That Return a Promise

The assertions we get from Protractor in the test above return promises, so we use Chai-as-promised to check that functions like isDisplayed and getText return what we expect after they’re resolved.

We can also deal with promises inside of unit tests. Take a look at this example, in which we test a modal that can be used to edit an existing widget. It makes use of the UI Bootstrap $modal service. When a user opens the modal, this service returns a promise. When she saves or cancels the modal, the promise is resolved or rejected. Here, we’ll test that the save and cancel methods are properly hooked up, again using Chai-as-promised.

// widget-editor-service.js
var angular = require('angular');
var _ = require('lodash');

angular.module('widgetProject.widgetEditor').service('widgetEditor', ['$modal', '$q', '$templateCache', function (
  $modal,
  $q,
  $templateCache
) {
  return function(widgetObject) {
    var deferred = $q.defer();

    var templateId = _.uniqueId('widgetEditorTemplate');
    $templateCache.put(templateId, require('./widget-editor-template.html'));

    var dialog = $modal({
      template: templateId
    });

    dialog.$scope.widget = widgetObject;

    dialog.$scope.save = function() {
      // Do some saving things
      deferred.resolve();
      dialog.destroy();
    });

    dialog.$scope.cancel = function() {
      deferred.reject();
      dialog.destroy();
    });

    return deferred.promise;
  };
}]);

This service loads the widget editor template into the template cache, loads a widget into it, and and sets up a deferred object that will be resolved or rejected depending on whether the user saves or cancels from
the editor. It returns a promise from the deferred.

Here’s how you might test something like this:

// test/unit/widget-editor-directive_test.js

var angular = require('angular');
var helpers = require('../test_helper');
var expect = helpers.expect;

describe('widget storage service', function() {
  beforeEach(function() {
    var self = this;

    self.modal = function() {
      return {
        $scope: {},
        destroy: self.sinon.stub()
      }
    }

    angular.mock.module('widgetProject.widgetEditor', { $modal: self.modal });
  });

  it('should persist changes when the user saves', function(done) {
    var self = this;

    angular.mock.inject(['widgetModal', '$rootScope', function(widgetModal, $rootScope) {
      var widget = { name: 'Widget' };
      var promise = widgetModal(widget);

      self.modal.$scope.save();

      // Somehow test that the widget was saved
      expect(self.modal.destroy).to.have.been.called;
      expect(promise).to.be.fulfilled.and.notify(done);
st
      $rootScope.$digest();
    }]);
  });

  it('should not save when the user cancels', function(done) {
    var self = this;

    angular.mock.inject(['widgetModal', '$rootScope', function(widgetModal, $rootScope) {
      var widget = { name: 'Widget' };
      var promise = widgetModal(widget);

      self.modal.$scope.cancel();
      expect(self.modal.destroy).to.have.been.called;
      expect(promise).to.be.rejected.and.notify(done);

      $rootScope.$digest();
    }]);
  });
});

To deal with the complexity of the promise that the modal returns in the widget editor test, we have to do a few things. First, we build a mock $modal service in the beforeEach function, replacing it with a function that returns $scope as an empty object, and stubs destroy. In angular.mock.module, we pass this modal double into the options to get Angular Mocks to use it instead of the real $modal service. This pattern is extremely useful in stubbing out dependencies, as we’ll discover shortly.

There are two examples here, and each has to wait for the promise returned by the widget editor to be resolved before it can be completed. Because of this, we have to pass done as parameter to the example
itself, and notify(done) when the test is complete.

Within the tests, we use Angular Mocks again to inject the widget modal and the AngularJS $rootScope service into the test. Having $rootScope gives us the ability to trigger a $digest loop. In each of the tests, we load up the modal, cancel or reject it, and use Chai-as-expected to test whether the promise returned was rejected or resolved. To trigger the actual promise resolution and call destroy, we have to have a $digest loop, so we do that at the end of each assertion as well.

We’ve now looked at how to deal with promises in both e2e and unit tests, using these assertions:

  • expect(foo).to.eventually.equal(bar)
  • expect(foo).to.be.fulfilled
  • expect(foo).to.be.rejected

Mocking Controller and Directive Dependencies

In the previous example, we had a service that relied on the $modal service, which we mocked out so that we could ensure that destroy was being called. The pattern we used to get that hooked up is very useful in
getting unit tests to work properly in Angular.

The pattern is as follows:

  • Set var self = this in the beforeEach block.
  • Build a double and stub its methods, then make it a property of the self object:
self.dependency = {
  dependencyMethod: self.sinon.stub()
}
  • Pass your doubles into the module under test:
angular.mock.module('mymodule', {
  dependency: self.dependecy,
  otherDependency: self.otherDependency
});
  • Check that the mocked methods within your test examples. You can use
    expect(foo).to.have.been.called.withArgs, passing in the arguments
    you expect, for more precise coverage.

Sometimes directives or controllers depend on many external and internal dependencies, and you need to mock them out. Here’s a more complicated example, in which directive watches a widgetStorage service and updates the widgets in its scope whenever the collection changes. There’s also an edit method that opens the widgetEditor we created above.

// widget-viewer-directive.js

var angular = require('angular');

angular.module('widgetProject.widgetViewer').directive('widgetViewer', ['widgetStorage', 'widgetEditor', function(
  widgetStorage,
  widgetEditor
) {
  return {
    restrict: 'E',
    template: require('./widget-viewer-template.html'),
    link: function($scope, $element, $attributes) {
      $scope.$watch(function() {
        return widgetStorage.notify;
      }, function(widgets) {
        $scope.widgets = widgets;
      });

      $scope.edit = function(widget) {
        widgetEditor(widget);
      });
    }
  };
}]);

Here’s how we might test something like this, mocking out the dependencies on widgetStorage and the widgetEditor:

// test/unit/widget-viewer-directive_test.js

var angular = require('angular');
var helpers = require('../test_helper');
var expect = helpers.expect;

describe('widget viewer directive', function() {
  beforeEach(function() {
    var self = this;

    self.widgetStorage = {
      notify: self.sinon.stub()
    };

    self.widgetEditor = self.sinon.stub();

    angular.mock.module('widgetProject.widgetViewer', {
      widgetStorage: self.widgetStorage,
      widgetEditor: self.widgetEditor
    });
  });

  // The rest of the test...
});

Accessing Child and Isolate Scopes

Sometimes you need to write a directive that has an isolate or child scope inside of it. For example, when using the Angular Strap $dropdown service, an isolate scope is created. It can be a pain to try to access these from within your tests. Knowing about self.element.isolateScope() is the key to solving this problem. Here’s an example using $dropdown, which creates an isolate scope:

// nested-widget-directive.js
var angular = require('angular');

angular.module('widgetSidebar.nestedWidget').directive('nestedSidebar', ['$dropdown', 'widgetStorage', 'widgetEditor', function(
  $dropdown,
  widgetStorage,
  widgetEditor
) {
  return {
    restrict: 'E',
    template: require('./widget-sidebar-template.html'),
    scope: {
      widget: '='
    },
    link: function($scope, $element, $attributes) {
      $scope.actions = [{
        text: 'Edit',
        click: 'edit()'
      }, {
        text: 'Delete',
        click: 'delete()'
      }]

      $scope.edit = function() {
        widgetEditor($scope.widget);
      });

      $scope.delete = function() {
        widgetStorage.destroy($scope.widget);
      });
    }
  };
}]);

Assuming this directive inherits the widget from a parent directive that has a collection of widgets, it can be tough to get ahold of the child scope to test its properties are being updated as expected. But it can be done. Here’s how:

// test/unit/nested-widget-directive_test.js
var angular = require('angular');
var helpers = require('../test_helper');
var expect = helpers.expect;

describe('nested widget directive', function() {
  beforeEach(function() {
    var self = this;

    self.widgetStorage = {
      destroy: self.sinon.stub()
    };

    self.widgetEditor = self.sinon.stub();

    angular.mock.module('widgetProject.widgetViewer', {
      widgetStorage: self.widgetStorage,
      widgetEditor: self.widgetEditor
    });

    angular.mock.inject(['$rootScope', '$compile', '$controller', function($rootScope, $compile, $controller) {
      self.parentScope = $rootScope.new();
      self.childScope = $rootScope.new();

      self.compile = function() {
        self.childScope.widget = { id: 1, name: 'widget1' };
        self.parentElement
        = $compile('<widget-organizer></widget-organizer>')(self.parentScope);

        self.parentScope.$digest();

        self.childElement = angular.element('<nested-widget
        widget="widget"></nested-widget>');

        self.parentElement.append(self.childElement);

        self.element = $compile(self.childElement)(self.childScope);
        self.childScope.$digest();
      }]);
    });

    self.compile();
    self.isolateScope = self.element.isolateScope();
  });

  it('edits the widget', function() {
    var self = this;
    self.isolateScope.edit();
    self.rootScope.$digest();
    expect(self.widgetEditor).to.have.been.calledWith(self.childScope.widget);
  });

Craziness, right? First we mock out the widgetStorage and widgetEditor again, then we proceed to create a compile function. This function will instantiate two scopes, a parentScope and a childScope, stub out a widget, and put it on the child scope. Then compile goes on to do some complicated template and scope setup: first, compiling a parent element called widget-organizer, which gets the parent scope passed into it. Once that’s all set up, we add a nested-widget child element to it, pass it the child scope, and trigger the $digest loop.

Finally, we get to the magic: we call the compile function, then hook into the compiled template’s isolate scope (which is the $dropdown scope), with self.element.isolateScope(). When we actually get to the assertion at the end, we can hook into the isolate scope to call edit, and finally check that the stubbed out widgetEditor was called with the stubbed widget.

Conclusion

Testing can get painful. I know that there were several times in our project where the pain of figuring out what to do was so great that it was tempting to just move on, writing code and falling back to the “click test” to make sure everything was working. Unfortunately, once you get out of that flow, the feeling of uncertainty begins to grow and grow.

After we took the time to figure out how to deal with these difficult cases, it became a lot easier to know what to do when similar complicated cases presented themselves. Armed with the patterns described in this article, we were able to get into a TDD workflow and move forward with confidence.

I hope that the testing patterns we’ve looked at today prove useful in your own development practice. AngularJS is still a young, growing framework. What other patterns have you found to make it easier to test? Please share them below!


Also published on Medium.