Why jasmine spy doesn't resolve the function object by reference?

问题

I have the following simple service

app.factory('Shoes', function() {
    function a() {return 12;}
    function b() {return a();}

    return {
      a: a,
      b: b
    }
  })

I want to test if the method a is being called when I call method b. My test looks like this:

describe('Testing a Shoes service', function() {
  var service;

  beforeEach(module('plunker'));

  beforeEach(inject(function(Shoes) {
    service = Shoes;
  }))

  it('.b should call .a', function() {
    spyOn(service, 'a');
    service.b();
    expect(service.a).toHaveBeenCalled();
  })

});

But the tests fail. Relevant plunker is here. I've already know how to resolve the problem in the plunker from those answers. Still there is one unresolved question:

Why does the original function object is not being resolved?

I thought that the system works like this (assuming spyies decorate the function with additional logic)

When I have no spies when I call service.a it's being resolved as:

A) service.a -> a()

and when I create a spy, it decorates the function

B) spy -> service.a => service.a*()

but the service.a is basically a reference for original a() so we should have a spy set for resolved function object in the end:

A + B => spy -> service.a -> a => a*()

回答1:

After you call spyOn(service, 'a'), service.a is no longer the a you defined in the function -- it is a spy function. That spy function happens to call a, but it is not a; it has a different identity and is a different function.

However, setting the a property of service does not change the function a you declared inside app.factory. You've simply changed service so that its a property no longer refers to your original a. By contrast, your b function never changes its reference to the original a. It gets a straight from the local app.factory scope in which a and b were originally declared. The fact that service replaces its original a with a spy does not affect b's call to a(), because it does not refer to service.a.

来源：https://stackoverflow.com/questions/36222909/why-jasmine-spy-doesnt-resolve-the-function-object-by-reference

标签

javascript

angularjs

jasmine