if you delete the package-lock.json and npm install tests do not work

[zhideng]

When you clone the project "npm run test" works. However if I delete the package-lock.json and perform an "npm i" to reinstall all the modules(a new lock file gets created) I get the following error:

TypeError: Super expression must either be null or a function

I was trying to use this guide to setup mocha based unit tests but was getting errors because I installed the node modules that were needed to run but my own project was throwing that error. As I troubleshooted I ended up finding out it was the package-lock.json file. I think this is important because users will be installing mocha unit testing dependencies and it will not run on their projects.

[eddyerburgh]

I've updated this. The problem is caused by vue-loader, which has a prettier dependency (See this issue vuejs/vue-cli#2128).

I've fixed vue-loader to version 12 in the example. The tests pass if you remove the package-lock and install, but I'll keep this open until the latest dependency versions can be used without this error.