See migration guide for breaking changes
https://github.com/webpack/webpack-dev-server/blob/master/migration-v4.md#migration-guide

The validate function no longer returns an array with errors, but just throws errors for invalid configs

The previous implementation resulted in the following error
`TypeError: The 'compilation' argument must be an instance of Compilation`

Instead of using a plain obj mock, use jest.mock to mock webpack.

merge commits Arnout

Also removed Webpack 4 support.

fix: TypeScript errors in StyleguidistOptionsPlugin

This fixes build error / failing npm ci command:
`npm ci` can only install packages when your package.json and package-lock.json or npm-shrinkwrap.json are in sync. Please update your lock file with `npm install` before continuing

…files

update test apps package.json

This package is not used anymore. Only examples-loader used
a method that has been removed in the latest loader-utils
version, but we rewrote that using standard Webpack 5 features.

Webpack 5 upgrade

There are almost no situations in which ReactDOM.render throws a synchronous
error. The only one currently is when the provided container is not a DOM
node, but that situation is impossible to cover in a test. It seems fine
to keep the catch clause here for when ReactDOM.render possibly changes in
the future, but we should ignore it w.r.t. test coverage.

merge codecov fixes

It was only used for a few webpack plugin types that have been replaced in #a949222

Eslint no-shadow https://eslint.org/docs/latest/rules/no-shadow

Disallow variable declarations from shadowing variables declared in the outer scope