Unable To Run Mocha Tests Because Return Is Outside Of Function?

I have been trying to setup mocha/chai tests for my vuex mutations. However, I get an error saying:

mutations.spec.js: 'return' outside of function (1:20)
> 1 | const _f38‍=exports;return _f38‍.r((function *(exports,require){"use strict";"main";let mutations;_f38‍.w("../src/View/store/modules/agenda/mutations",[["mutations",["mutations"],function(v){mutations=v}]]);let expect;_f38‍.w("chai",[["expect",["expect"],function(v){expect=v}]]);yield;

My mutations.js file is:

const setEditedItemIndex = (state, newIndex) => {
    state.editedIndex = newIndex;
};

export default {
    setEditedItemIndex
}

My mutations.spec.js file is

import { mutations } from '../src/View/store/modules/agenda/mutations';
import { expect } from 'chai';




describe('mutations', () => {
    it ('should change the edited item index', () => {
        const state = { editedIndex: -1 };
        mutations.setEditedItemIndex(state, 1); 
        expect(state.editedIndex).to.equal(1);
    })
})

and the command I am running is

./node_modules/mocha/bin/mocha -r esm  -r @babel/register './test/**/*.spec.js'

I have tried the solution as documented in this comment, but that doesn't work and the next solution seems to point to a read only project.