Jasmine Tutorial: Unit Testing Promises In Services

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So recently I’ve been doing a lot of Angular unit tests with Jasmine and Grunt. I have to say, testing promises is extremely frustrating and most of the examples I found out there either 1) didn’t work or 2) wouldn’t allow you to test content in a then block if you had multiple chained promises, or if you had a promise being called from and returned from another service. After many hours of frustrating trial and errors I found a solution I’m happy with so I want to share.

Let’s assume this is your controller:

'use strict';

angular.module('myModule').controller('myCtrl', ['$scope', 'api',
function ($scope, $api) {

  $scope.data = null;
  $scope.message = null;

  /**
  * Load some data from the API service
  * @return boolean
  **/
  $scope.loadData = function () {

    var config = {
      method: 'GET',
      url: 'http://api.domain.com/someRESTfulEndpoint',
      headers: {'Content-Type': 'application/json'},
      data: null
    };

    return $api.load(config).then(function (request) {
      if (request) {
        $scope.message = 'Your data was successfully loaded';
        $scope.data = request.response;
        return true;
      } else {
        $scope.message = 'The API service failed';
      }
      return false;
    });
  };
}]);

And here is the service making your API calls:

'use strict';

angular.module('myModule').service('api', ['$rootScope', '$http',
  function ($rootScope, $http) {

    /**
    * Makes the $http request given the proper configuration options
    * @param Object configruation for the $http request
    * @return Object $http promise that resolves to request payload or error
    **/
    this.load = function (options) {
      return $http({
        method: options.method || 'GET',
        url: options.url || 'http://api.domain.com/someDefaultEndpoint',
        headers: options.headers || null,
        data: options.data || null
      }).then(
        function (request) {
          //we got a response back, return just the API payload data
          if (request.status === 200 && request.data) {
            return request.data;
          } else {
            return {
              results: false,
              message: 'API request error',
              response: request
           };
         }
       }
     );
   };
}]);

Finally, this is your working unit tests:

'use strict';

describe('testing myModule', function () {

  beforeEach(module('myModule'));

  var $controller, $rootScope, $scope, $api, $httpBackend, $q;

  beforeEach(
    inject(function (_$controller_, _$rootScope_, api, _$httpBackend_, _$q_) {
      $controller = _$controller_;
      $rootScope = _$rootScope_;
      $httpBackend = _$httpBackend_;
      $q = _$q_;
      $api = api;
      $scope = $rootScope.$new();

      $httpBackend.when('GET').respond('test http GET call');
      $httpBackend.when('POST').respond('test http POST call');

      $controller('myCtrl', {
        $scope: $scope,
        $api: $api
      });
    })
  );

  it('has a $scope.loadData() function', function() {

    var testConfig = {
      method: 'POST',
      url: 'http://api.domain.com/endpoint',
      data: { some: 'data'}
    };

    var fakeData = { data: 'is fake' };

    //we spy on the API service and also return a fake promise call
    spyOn($api, 'load').and.callFake(
      function() {
        var deferred = $q.defer();
        deferred.resolve({result: true, response: fakeData});
        return deferred.promise;
      });
    });

    $scope.loadData(testConfig); //call the function we're testing in the controller
    $scope.$apply(); //we have to call this so Angular will try and resolve the promise
    expect($api.load.calls.count()).toEqual(1); //make sure it's called the api service
    expect($scope.message).toEqual('Your data was successfully loaded');
    expect($scope.data).toEqual(fakeData);
  });

  it('returns an error if the API fails', function() {

    var testConfig = {
      method: 'POST',
      url: 'http://api.domain.com/endpoint',
      data: { some: 'data'}
    };

    spyOn($api, 'load').and.callFake(
      function() {
        var deferred = $q.defer();
        deferred.resolve({
        result: false,
        message: 'api error'
      });
      return deferred.promise;
    });

    $scope.loadData(testConfig);
    $scope.$apply();
    expect($scope.message).toEqual('api error');
    expect($api.load.calls.count()).toEqual(1);
  });
});