Using ngMock to simulate $http calls in service unit tests

Question

I've been looking at this for hours. I've tried example after example. I just can't seem to get this to work. Please help =)

I am doing all this on a clean clone of the angular-seed repo (git://github.com/angular/angular-seed.git). I have made no changes except those listed below.

Problem:

When I run the following, the test works. Note that in this version, the service returns a value before doing any kind of $http call.

./app/js/services/services.js

'use strict';
angular.module('myApp.services', [])
  .factory("exampleService", function ($http) {
    return {value:"goodValue"};

    $http.get("/exampleUrl")
      .success(function () {
        return {value:"goodValue"};
      })
      .error(function () {
        return {value:"badValue"};
      })
  });

./test/unit/servicesSpec.js

'use strict';
describe('service', function() {
  var $httpBackend;

  beforeEach(module('myApp.services'));

  beforeEach(inject(function ($injector) {
    $httpBackend = $injector.get("$httpBackend");
    $httpBackend.when("GET", "/exampleUrl")
      .respond({value:"goodValue"});
  }));

  afterEach(function () {
    $httpBackend.verifyNoOutstandingExpectation();
    $httpBackend.verifyNoOutstandingRequest();
  });

  describe('exampleService', function () {
    it('.value should be "goodValue"', inject(function (exampleService) {
      expect(exampleService.value).toEqual("goodValue");
    }));
  });
});

Results

info (watcher): Changed file "/home/username/mocktest/test/unit/servicesSpec.js".
Chrome 26.0: Executed 5 of 5 SUCCESS (0.136 secs / 0.035 secs)

When I remove the line return {value:"goodValue"}; and actually let it run the $http.get(), the whole thing breaks with the following errors:

info (watcher): Changed file "/home/username/mocktest/app/js/services.js".
Chrome 26.0 service exampleService .value should be "goodValue" FAILED
  TypeError: Cannot read property 'value' of undefined
      at null.<anonymous> (/home/username/mocktest/test/unit/servicesSpec.js:22:28)
      at Object.invoke (/home/username/mocktest/app/lib/angular/angular.js:2864:28)
      at workFn (/home/username/mocktest/test/lib/angular/angular-mocks.js:1758:20)
  Error: Declaration Location
      at window.jasmine.window.inject.angular.mock.inject (/home/username/mocktest/test/lib/angular/angular-mocks.js:1744:25)
      at null.<anonymous> (/home/username/mocktest/test/unit/servicesSpec.js:21:40)
      at null.<anonymous> (/home/username/mocktest/test/unit/servicesSpec.js:20:3)
      at /home/username/mocktest/test/unit/servicesSpec.js:4:1
  Error: Unflushed requests: 1
      at Error (<anonymous>)
      at Function.$httpBackend.verifyNoOutstandingRequest (/home/username/mocktest/test/lib/angular/angular-mocks.js:1225:13)
      at null.<anonymous> (/home/username/mocktest/test/unit/servicesSpec.js:17:18)
Chrome 26.0: Executed 5 of 5 (1 FAILED) (0.14 secs / 0.043 secs)

Thoughts

I suspect I need to do some kind of returning of a promise object in the service, then resolve it afterwards, but I have no idea what that would be. Any help appreciated.

Answer 1

Your suspected solution was on the right track - promises were the key to fixing the errors/failing tests.

Using your original $http service to conditionally return the factory object didn't work because you were effectively returning nothing from your factory function (due to the asynchronous promise resolution of $http).

I considered just putting return in front of your original $http.get() call. But that isn't the desired behavior, because the AngularJS .factory method should return a service object that you define, not an mere promise returned by the call to $http.

The solution is exposing a method on your exampleService object that can be called by your app. That getData() method returns a promise (via $http) which your app/test can handle asynchronously using .success() or .error()

./app/js/services/services.js

'use strict';
angular.module('myApp.services', [])
    .factory("exampleService", function ($http) {
        return {
            getData: function () {
                return $http.get("/exampleUrl");
            }
        }
  });

./test/unit/servicesSpec.js

'use strict';
describe('service', function() {
  var $httpBackend;

  beforeEach(module('myApp.services'));

  beforeEach(inject(function ($injector) {
    $httpBackend = $injector.get("$httpBackend");
    $httpBackend.when("GET", "/exampleUrl")
        .respond(200, {value:"goodValue"});
  }));

  afterEach(function () {
    $httpBackend.flush()
    $httpBackend.verifyNoOutstandingExpectation();
    $httpBackend.verifyNoOutstandingRequest();
  });

  describe('exampleService successful http request', function () {
    it('.value should be "goodValue"', inject(function (exampleService) {

        exampleService.getData().success(function(response) {
          expect(response.value).toEqual("goodValue");
        }).error( function(response) {
          //should not error with $httpBackend interceptor 200 status
          expect(false).toEqual(true);
        });

    }));
  });


});

Note that Destron's comment about $httpBackend.flush() was also important to get the mock backend to intercept the $http.get() request from your service.

Hope that helps.