A simple AngularJS service with its unit test, taking in consideration than an API object was handled to the service.

users.js

"use strict";

angular.module('usersResources', [
  'apiConstants',
  'apiModule'
  ])
.service('usersResources.users', [
  '$q',
  'api',
  function users($q, api) {
    var _self = this;
    this.getUsersURI = function() {
      return '/user';
    }
    this.getUsers = function() {
      var deferred = $q.defer();      
      api.get(_self.getUsersURI()).then(function(usersResponse){
        deferred.resolve(usersResponse);
      }, function() {
        deferred.reject.apply(null, Array.prototype.slice.call(arguments));
      });
      return deferred.promise;
    }
}]);

//////////////////////// Unit Test /////////////////////////
"use strict";

ddescribe('[Service] Users Resources', function () {
  var componentName = 'usersResources.users';
  var succesfulApiResponse = 'Successful Response From API';
  var failedApiResponse = 'Failed Response From API';

  beforeEach(module('usersResources'));

  describe(' :: User Resources Actions', function() {    
    var httpBackend, users, apiUrl, api, q, rootScope;
    var mockedApiDeferred, mockedDeferred;

    var mockApi = function() {
      var deferred = q.defer();
      spyOn(api, 'get').andReturn(deferred.promise);
      return deferred;
    }

    var mockQ = function() {
      var deferred = jasmine.createSpyObj('deferred', ['resolve', 'reject']);
      spyOn(q, 'defer').andReturn(deferred);
      return deferred;
    }

    beforeEach(inject(function ($injector, $q, $rootScope) {
      users = $injector.get(componentName);
      apiUrl = $injector.get('apiBaseUrl');
      api = $injector.get('api');
      q = $q;
      rootScope = $rootScope;

      mockedApiDeferred = mockApi();
      mockedDeferred = mockQ();
    }));


    it('should perfom an API GET call to the users REST Users Endpoint so it can resolve the server\'s response on success', function() {
      users.getUsers();
      mockedApiDeferred.resolve(succesfulApiResponse);
      rootScope.$digest();

      expect(mockedDeferred.resolve).toHaveBeenCalledWith(succesfulApiResponse);
      expect(api.get).toHaveBeenCalledWith(users.getUsersURI());
    });

    it('should perform an API GET call to the users REST Users Endpoint so it can reject the server\'s response on failure', function() {
      users.getUsers();
      mockedApiDeferred.reject(failedApiResponse);
      rootScope.$digest();

      expect(mockedDeferred.reject).toHaveBeenCalledWith(failedApiResponse);
      expect(api.get).toHaveBeenCalledWith(users.getUsersURI());
    })

  })
})