角度单元测试，SpyOn独立功能

Question

I am using Jasmine to test an Angular app and would like to test that the getItem() function within my controller is called when the ready() function of the controller is called.

--- Controller ---

var vm = this;
vm.items = [];
$ionicPlatform.ready(ready);

function ready() {
     vm.items.push(getItem());

     function getItem(){
          var item = //do stuff to get item;
          console.log('getItem called');
          return item;
     }
}

--- Spec ---

describe('Controller', function(){

     //--- Load app with dependencies and module to test code omitted.

     beforeEach(function(){
          //How do I spy on getItem() to test that it was called?
          //I've tried getItem = jasmine.createSpy()
          //I've tried spyOn(window, 'getItem')
     }

     //--- Initialize the controller and a mock scope code omitted.

     beforeEach(function(done){
          $ionicPlatform.ready(function(){
               done();
          });
     });

     it('getItem function should get called', function(){
          expect(getItem).toHaveBeenCalled();

          //--- Note, getItem does not get called according to the expect statement, 
          //--- but does output 'getItem called' to the terminal when running the test.
     });

});

Answer 1

Unfortunately, you've come upon a fundamental limit of Javascript unit testing with Jasmine-- you can only spyOn methods that are exposed on some object. If there is a function that is internal to another function, and not exposed in anyway, you cannot test it directly.

However, you do have two options available to you:

1. Expose the function in a way that it can be spied on (generally as a method of whatever Angular component you are testing).
2. Test it indirectly.

The first is probably relatively self-evident, but the latter may be a little confusing. Basically, you can't test directly if the getItems function is called, but the function may have downstream methods it calls or values it changes you can test. For instance, you can test that vm.items.push is larger after ready is called, or you can spyOn(console.log) and expect(console.log).toHaveBeenCalledWith('getItem called') .

You can find arguments for both approaches on the internet-- I tend to prefer approach two because I don't like doing refactors solely for the purpose of testability, but many will argue that refactoring for testability generally yields better code. That choice is yours to make. Hope this helps!