Angular js use of controller in this example - angularjs

Question

I am reading the Angular JS documentation I am looking at this example:
// testing controller
describe('MyController', function() {
var $httpBackend, $rootScope, createController;
beforeEach(inject(function($injector) {
// Set up the mock http service responses
$httpBackend = $injector.get('$httpBackend');
// backend definition common for all tests
$httpBackend.when('GET', '/auth.py').respond({userId: 'userX'}, {'A-Token': 'xxx'});
// Get hold of a scope (i.e. the root scope)
$rootScope = $injector.get('$rootScope');
// The $controller service is used to create instances of controllers
var $controller = $injector.get('$controller');
createController = function() {
return $controller('MyController', {'$scope' : $rootScope });
};
}));
My question is what purpose the createController serves, I don't really understand why it is there or what the last line does where $controller is returned or what it has to do with the $scope.
It is the second grey section that contains code underneath the header: Unit testing with mock $httpBackend.
Help would be greatly appreciated.

Answer 1

$controller returns an instance of MyController from the first grey section. To give the controller some context, it passes the $rootScope into the instantiation of the controller. Hence when you execute the controller (as shown in subsequent it() blocks) the controller runs and kicks off the $http.get('/auth.py') request.