Angular: Mock a Login with $auth

I'm trying to work out how to unit test my login controller with Karma/Jasmine/Mocha.

I basically want to test if a 200 comes back from the $auth.login() then the message saved should be equal to "successfully logged in", otherwise if I receive a 401 then the message that comes back should be "error logging in".

This is where I've gotten up to so far:

login-controller.js

function loginCtrl($auth, $scope, $rootScope) {
    var vm = this;

    vm.login = function() {
        var credentials = { email: vm.email, password: vm.password };

        $auth.login(credentials).then(function() {
            $scope.message = "successfully logged in";
        }, function(error) {
            $scope.message = "error logging in";
        })
    };
}

spec.js

describe('Login Controller', function() {
  var rootScope, scope, controller, location, $auth;

  beforeEach(function() {
    bard.appModule('app.login');
    bard.inject('$rootScope', '$controller', '$location', '$auth');
  });

  beforeEach(function() {
    rootScope = $rootScope;
    scope = $rootScope.$new();
    auth = $auth;
    controller = $controller('authCtrl', { $scope: scope });
  });

  it('should return a success message when successfully logged in', function() {
    rootScope.$apply()
    expect(scope.message).to.equal("successfully logged in");
  });

  it('should return an error message when not logged in', function() {
    rootScope.$apply()
    expect(scope.message).to.equal("error logging in");
  });
});

Do I need to explicitly pass the status codes, or is there a better way to mock this?

Any help is appreciated. Thanks in advance!