Weird Mocha behavior regarding scope

bestPractices.js

/*
  Running code on Chrome's console, the output on line 10 is "undefined" as we're wrapping everything inside an IIFE,
  which creates a new scope so nothing is exposed to the global scope unless its intentional like we did on line 9.
*/
(function() {
    let myObject = {
        name : 'Jory'
    };
    window.myWindowObject = {
      name: 'Kaue'
    }
    return myObject;
}());
console.log(window.myObject); // undefined
console.log(window.myWindowObject); // Object {}

/*
  For some reason an IIFE does not create a new scope in Mocha.
  So everything inside an IIFE is being exposed to the global scope
*/
(function() {
    let myObject = {
        name : 'Jory'
    };
    window.myWindowObject = {
      name: 'Kaue'
    }
    return myObject;
}());
console.log(window.myObject); // Object {}
console.log(window.myWindowObject); // Object {}