I did read this part but did not take it seriously. Wasted so much time for neglecting this. The vue’s mocka-webpack example repo on: https://github.com/vuejs/vue-test-utils-mocha-webpack-example uses `webpack: ^3.6.0`.
The webpack installed with
npm i -D webpack is
npm install mocha-webpack@next did solve my problem.
Another lesson for why you should pay attention to versions learned in a hard way.
Anyways THANKS FOR THE ARTICLE!