How to spyOn a function? - angularjs

Question

I have a directive that look like this:
angular.module('myApp', [])
.directive('myDirective', ['$window','MyConfig', function($window,MyConfig){
return {
link: function(scope, element, attr, controller) {
var w = angular.element($window);
function adjustTop(){
var oldtop = scope.top;
if(oldtop<15){
scope.top += 2;
}else{
scope.top = 0;
}
}
if(MyConfig.adjusttop){
w.bind('scroll', function () {
adjustTop();
});
};
}
};
}]);
How can I spyOn to detect adjustTop() function have been called when MyConfig.adjusttop is true?

Answer 1

You shouldn't do that. Testing private members arguably isn't a good idea because it couples your tests to a specific implementation, making them fragile.
In general you should test what your code does, not how it does it. In this case, you could write tests to ensure the scope.top property is correctly updated after the scroll event has been triggered.
Updated to address OP's comment:
Here's a way for you to test what you want:
describe('my test', function() {
var $scope, $window, $compile, MyConfigMock;
beforeEach(function() {
module('plunker');
MyConfigMock = {};
module(function($provide) {
$provide.value('MyConfig', MyConfigMock);
});
inject(function($rootScope, _$window_, _$compile_) {
$scope = $rootScope;
$window = _$window_;
$compile = _$compile_;
});
});
it('updates top on scroll if set to do so', function() {
// Arrange
MyConfigMock.adjusttop = true;
$scope.top = 15;
$compile('<my-directive></my-directive>')($scope);
// Act
$($window).trigger('scroll');
// Assert
expect($scope.top).toBe(0);
});
});
Working Plunker