So I have a view, it's the end of a login page, 'login' being my controller

<!-- ... -->

   <button type="submit" class="col-sm-6 col-sm-12" ng-disabled="login_form.$invalid" class="btn btn-primary">Log in</button>

    <div class="col-sm-12 alert alert-warning" ng-show="login.failed()">
        Bad username, email or password
    </div>
    <div class="col-sm-12 alert alert-warning" ng-show="login.error()">
        Something went wrong... The guru's probably meditating.
    </div>

/* Login Controller definition */
/* Here I'm injecting an 'auth' service to implement RESTAPI calls */

ar.module('frontendApp')
  .controller('LoginCtrl', ['$scope', 'auth', function ($scope, auth) {
    var self = this;

    this._response = undefined;
    this.remember_me = false;
    this._error = false;

	/*	Called on a button click */
    this.login = function () {
      self._response = undefined;
      self._error = false;
      /* I'm trying to auth, then set _response with the answer */
      auth.login(self.user, self.remember_me).then(function (answer) {
        self._response = answer;
      }, function (data) {
        console.error('LoginCtrl: error caught. Something went wrong.');
        console.error('data', data);
        self._error = true;
      });
    };

	/*	These are the methods called by warnings, they use self._response */
    this.failed = function () {
      return self._response != undefined && !self._response.authentified;
    };

    this.error = function () {
      return self._error;
    };

  }]);

/* This is my 'auth' service */

angular.module('frontendApp')
  .service('auth', ['$http', function ($http) {
    var self = this;

    this.login = function (user, remember_me) {
      remember_me = remember_me === undefined ? false : remember_me;

      user.username = user.login; /* TODO: useless once converted to express - test only */
      /*	Return a promise that is solved if the response from the server makes sense.  */
      return new Promise(function (accept, reject) {
        try {
          $http.post(SERVER_PREFIX + 'login', user).then(function (data) {  //  On accept
            expect(data.data).to.contain.keys('id', 'userId');
            accept({
              authentified: true,
              user: user,
              answer: data.data
            });
          }, function (data) {  //  On rejected
            expect(data.data).to.contain.keys('error');
            expect(data.data.error).to.contain.keys('status', 'code');
            expect(data.data.error.code).to.equal('LOGIN_FAILED');
            accept({
              authentified: false,
              user: user,
              answer: data.data
            });
          });
        }
        catch (error) {
          if (error instanceof AssertionError) reject(error.data); // Bad data sent by the server
          else throw error;
        }
      });
    };
  }]);