Same here - I am really unsure how to get started with mocha-webpack testing a Vue application using laravel mix.
I can get the most basic tests running with just a webpack config file to use vue-loader on .vue files, but as soon as I need something more, I run into problems and assume I have to load the same webpack configuration as the dev/production builds - but how?
I found that if I use mix.extract() it will fail with this message. By adding a cross-env NODE_ENV=testing and testing for this environment in the mix config file, I can make this only run in non-testing environments - and the error is dispersed.