call function via closure vs call on es6 module. How to mock?

Hi guys I created a stackoverflow issue but I think I can get a better answer in here.

http://stackoverflow.com/questions/38579934/js-call-function-via-closure-vs-call-on-es6-module?noredirect=1#comment64549051_38579934

I have 2 functions defined like this:

export function builder(){ ... };
export function action() { return () => builder() };

Now I am trying to write a test that mock the builder function and return {};

 import * as m from 'redux/modules/mymodule';

 it('call buildSolrUrl', () => {
  const spy = expect.spyOn(m, "builder").andReturn({});
  m.action()();
  expect(spy.calls.length).toEqual(1);
 });

The problem is that builder does not get mock in that case. If I change my code for:

export function action() { return () => this.builder() };

The method is mocked but my program does not work anymore because action() return a function that is executed later and this is not resolved to the right object.

To resume: My code works because the call to builder() is done via closure. The tests are unable to mock the function that way because the function is called via the closure.

What is the best way to deal with this?

[awei01]

@casertap You’re going to have to refactor your file with exports. I believe this will work, but not tested. It’s also a bit of an ugly hack, but I don’t see any other way around it:

File with your library

const lib = {}

function doSomething(param) {
    const { useDoSomething } = lib
    return useDoSomething(param)
    // or return lib.useDoSomething(param)
}

function useDoSomething(param) {
    return param
}

lib.doSomething = doSomething
lib.useDoSomething = useDoSomething

export default lib

[ljharb]

You can’t mock out exported functions - you can only mock properties on objects.

You either have to not mock builder - or, export default an object with properties, and make sure the “action” function looks up at runtime the “builder” function on that object. Then, you can mock out that object.