How to have a mock controller pass data to a directive with Jasmine

I am trying to unit test a directive with Jasmine:

app.directive('helloWorld', function() {
  return {
    restrict: 'E',
    scope: {
      messages: '=',
      onSelect: '&'
    },
    template: '<a ng-repeat="message in messages track by $index" href="" ng-click="onSelect({message: message})">Test: {{ message.name }}</a>',
    link: function(scope) {
    }
  }
});

Ideally, I would like to pass in some mock data for messages, and ensure that the DOM element in the directive is correctly populated.

But I cannot understand how to get the template to compile with the mock data. Specifically, messages: '&' means that the directive is watching whenever the controller updates messages. Here is the test:

describe('Directive: HelloWorld', function() {
    var $scope, ctrl, $compile, $rootScope;

    beforeEach(module('app'));

    beforeEach(inject(function(_$rootScope_, $controller, _$compile_) {
      $rootScope = _$rootScope_;
      $compile = _$compile_;
      $scope = $rootScope.$new();

      ctrl = $controller('MainCtrl', {
        $scope: $scope
      });
    }));

    it('should list three messages', function() {
      ctrl.messages = [{name: 'foo'}, {name: 'bar'}, {name: 'foobar'}];
      var template = '<hello-world messages="messages" on-select="ctrl.foo(message)"></hello-world>';
      var element = $compile(template)($scope);
      $rootScope.$digest();

      expect(element.children().length).toBe(3);
    });
  });

Here is the plunker: https://plnkr.co/edit/8Jy4eGXotduGvBsr8jkN?p=preview

I have looked at many SO questions, but I cannot yet make sense of it. How can I pass on data to the mock controller so that the template has access to it?

Update I modified my Plunker to do this: $scope.messages = [{name: 'foo'}, {name: 'bar'}, {name: 'foobar'}]; instead of ctrl.messages = .... It works fine now.