Before writing your tests for step 4, Scott notes we need to update our karma.conf.js file. Afterwards, when running npm start you might get an error saying "cannot load webpack".
My Fix: I removed all the karma packages from my devDependencies in my package.json file & node_modules folder:
npm uninstall --save-dev karma karma-chai karma-chrome-launcher karma-mocha karma-mocha-reporter karma-sourcemap-loader karma-webpack
Next just install the new packages
npm install --save-dev karma karma-chai karma-chrome-launcher karma-mocha karma-mocha-reporter karma-sourcemap-loader karma-webpack