Stubbing method in same file using Sinon

Question

I'm trying to unit test a function in a file while stubbing another function in the SAME file, but the mock is not being applied and the real method is being called. Here's an example:

// file: 'foo.js'

export function a() {
   // .....
}

export function b() { 
   let stuff = a(); // call a
   // ...do stuff
}

And my test:

import * as actions from 'foo';

const aStub = sinon.stub(actions, 'a').returns('mocked return');
actions.b(); // b() is executed, which calls a() instead of the expected aStub()

Answer 1

Some restructuring can make this work.

I've used commonJS syntax. Should work in the same way in ES6 as well.

foo.js

const factory = {
  a,
  b,
}
function a() {
  return 2;
}

function b() {
  return factory.a();
}

module.exports = factory;

test.js

const ser = require('./foo');
const sinon = require('sinon');

const aStub = sinon.stub(ser, 'a').returns('mocked return');
console.log(ser.b());
console.log(aStub.callCount);

Output

mocked return

1

Answer 2

While the above does work, it's definitely a workaround as my linter was quick to inform.

I ended up separating modules and using proxyquire. This library allows you to easily substitute any / all exports with those of your choosing, sinon stub spy or mocks included. e.g. :

in b.js

export const fnB = () => 'hey there!';

in a.js

import { fbB } from 'b.js';
export const fnA = () => fbB();

in a.test.js

import { noCallThru } from 'proxyquire';
const proxyquireStrict = noCallThru();
const stubB = stub().returns('forced result');
const moduleA = proxyquireStrict('a.js', {
    'b.js' : { fnB: stubB }
}).fnA; 

console.log(fnA()); // 'forced result'