Stub an export from a native ES Module without babel

Question

I'm using AVA + sinon to build my unit test. Since I need ES6 modules and I don't like babel, I'm using mjs files all over my project, including the test files. I use "--experimental-modules" argument to start my project and I use "esm" package in the test. The following is my ava config and the test code.

  "ava": {
    "require": [
      "esm"
    ],
    "babel": false,
    "extensions": [
      "mjs"
    ]
  },


// test.mjs
import test from 'ava';
import sinon from 'sinon';
import { receiver } from '../src/receiver';
import * as factory from '../src/factory';

test('pipeline get called', async t => {
  const stub_factory = sinon.stub(factory, 'backbone_factory');
  t.pass();
});

But I get the error message:

  TypeError {
    message: 'ES Modules cannot be stubbed',
  }

How can I stub an ES6 module without babel?

Answer 1

Sinon needs to evolve with the times or be left behind (ESM is becoming defacto now with Node 12) as it is turning out to be a giant pain to use due to its many limitations.

This article provides a workaround (actually 4, but I only found 1 to be acceptable). In my case, I was exporting functions from a module directly and getting this error: ES Modules cannot be stubbed

export function abc() {

}

The solution was to put the functions into a class and export that instead:

export class Utils {
  abc() {
  
  }
}

notice that the function keyword is removed in the method syntax.

Happy Coding - hope Sinon makes it in the long run, but it's not looking good given its excessive rigidity.