Fetch with Mocha.js in browser mode won't process or throw error

I'm pretty new to the whole 'modern' JS (implying, TS, TDD, Node...) so bear with me please :)

Anyhow, part of my app includes fetching data from the back-end and processing it with Three.js, I tried a lot of things from the docs, but each time it compiles fine, but nothing is displayed in the browser (nor in the console).

Also tried chai-as-promised, async syntax (but I understand that it's for Node)...

I'd love some pointers on what I'm doing wrong, I'm starting to wonder if that even possible, even though, as far as I know the code is valid JS, that [runs into my browser] (latest FF).

Thanks in advance.

it('A test what should fetch from the local api a json file', function(done) {
            // The url is just a random service I'm using for temporal test purpose
            fetch('https://baconipsum.com/api/?type=meat-and-filler')
                .then(function(response) {
                    return response.json();
                })
                .then(function(data) {
                    if (data) {
                        done();
                    } else {
                        done('err');
                    }
                });
        });