I had to make a few changes to my webpack.config.js before I can follow the tutorial without problems. Also using laravel-mix's webpack.config.js was not an option. So here is how my webpack.config.js file looks with the following package versions:

"devDependencies": {
    "@vue/test-utils": "^1.1.3",
    "jsdom": "^16.5.1",
    "jsdom-global": "^3.0.2",
    "vue-loader": "^15.9.6",
    "vue-template-compiler": "^2.6.12",
	"mochapack": "^2.0.6",
},
"scripts": {
    "test": "mochapack --webpack-config=webpack.testing.config.js --require tests/setup.js tests/**/*.spec.js"
}

// webpack.config.js
const { VueLoaderPlugin } = require('vue-loader')

module.exports = {
    target: 'node',
    module: {
        rules: [
            {
                test: /\.vue$/,
                loader: 'vue-loader',
                options: {
                    optimizeSSR: false
                }
            },
        ]
    },

    plugins: [
        new VueLoaderPlugin()
    ]
}

And the setup.js file as follows

// setup.js
const Vue = require('vue')
Vue.config.devtools = false
require('jsdom-global')()

Test Single File Components