AngularJS Unit Testing for services?

This is my code. How would you test this service ? Thanks a lot.

angular.module('srv.login', ['srv.backend'])

     .service('loginService', function ($q,backendService,transformRequestAsFormPost) {

         this.login = function (user) {

            var deferred = $q.defer();
            var headers  = {
              'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8',
              'Content-Type': 'application/x-www-form-urlencoded'
        }


          backendService.post('login.do', user, transformRequestAsFormPost, headers).then(
            function (result) {

                deferred.resolve(result);
            },
            function (error) {
                deferred.reject(error);
            });

           return deferred.promise;
        }
});

I'd really appreciate some examples well. Thanks in advance