Angular and Jasmine: how to mock a service that returns a promise

Question

I have the following controller in AngularJS that is invoking a service provided by "$mdSidenav" from Angular Material. This is service is provided by a factory method.

angular.module('leopDirective', [])
    .controller('MenuCtrl', function ($scope,$timeout,$mdSidenav,$log) {

    $scope.mdSidenav = $mdSidenav;
    $scope.close = function () {
        $mdSidenav('left').close().then(function() {$scope.closed=true; });
    };

});

I am trying to mock that service ($mdSidenav) in order to test my controller. The following is the source code of the Jasmine test that I am trying to define:

describe('Controller: MenuCtrl', function() {
    var $rootScope, $scope, $controller, $q, menuCtrl,
        mock__mdSidenav = function(component) {
            return {
                // THIS FUNCTION IS EMPTY SINCE $Q IS NOT AVAILABLE
                close: function() {}
            }
        };

    beforeEach(function() {
        module('leopDirective', function($provide) {
            // I HAVE TO PROVIDE THE MOCK UP BEFORE INJECTING $Q
            $provide.value('$mdSidenav', mock__mdSidenav);
        });
        inject(function($injector) {
            $rootScope = $injector.get('$rootScope');
            $controller = $injector.get('$controller');
            $q = $injector.get('$q');
            $scope = $rootScope.$new();
        });
        menuCtrl = $controller("MenuCtrl", { $scope: $scope });
    });

    it('should create the $mdSidenav object', function() {
        var deferred = $q.defer(),
            promise = deferred.promise;
        // NOW THAT $Q IS AVAILABLE, I TRY TO FILL UP THE FUNCTION
        mock__mdSidenav.close = function() {
            return promise.then(function(response){return response.success;});
        };
        // force `$digest` to resolve/reject deferreds
        $rootScope.$digest();
        // INVOKE FUNCTION TO TEST
        $scope.close();
    });
});

The problem that I have is that I do not know how to create a function for the mock that returns a promise:

creating a promise depends on $q,
$q has to be injected from within the block "inject",
however, $provide has to be used within "module", just before "inject",
therefore, the function that returns a promise within my mock object (mock__mdSidenav().close()), has to be empty at the before invoking "$provide" and, somehow, created later on.

With this approach, the error that I am getting is the following error (see Demo plnkr), which is telling me that creating the empty function first and filling it later does not work:

TypeError: Cannot read property 'then' of undefined
    at Scope.$scope.close (app.js:7:35)

What is the correct way to mock a service that has a function that returns a promise?

dfsq dfsq · Accepted Answer · 2015-05-02T17:15:37

First of all, make mock service method return Promise object:

mock__mdSidenav = function(component) {
  return {
    isMock: true, 
    close: function() {
        return $q.when();
    }
  }
};

Then inject it into controller instance:

menuCtrl = $controller("MenuCtrl", { 
    $scope: $scope,
    $mdSidenav: mock__mdSidenav
});

And finally, write some expectation:

it('should create the $mdSidenav object', function() {

  $scope.close();
  $rootScope.$digest();

  expect($scope.closed).toBe(true);
});

Demo: http://plnkr.co/edit/dr79GgZYG2tjiuWU0oFx?p=preview

Angular and Jasmine: how to mock a service that returns a promise

1 Answers