Add it to your project as a developer dependency. And run it like
webpack-dev-server from the command line or as a
npm install --save-dev jest-webpack
yarn add -D jest-webpack
Add it as a
Run it with jest options
npm test -- --testPathPattern test-just-this-file
jest-webpack currently works with a lot of jest options out of the bag since there is no special handling needed and they can just be passed to jest by the tool. You can see what is so far specifically tested so far in https://github.com/mzgoddard/jest-webpack/issues/3.
How it works?
jest-webpack uses a webpack plugin to add related plugins that are responsible for 4 operations.
TestEntriesPluginfinds test files that jest will operate on and creates entry chunks for them.
EntryReferencePlugincreates additional entries for any other files that are depended on by those test files. These entries return objects pointing to the various transformations of that file. If a css file is depended on by both
css-loader/localsfor example, both of the outputs of those loaders will be in the same file. Files then depending on those outputs reference the entry chunk and use the exported member for their needed version of the original file.
EmitChangedAssetsPluginremoves entry chunks that already exist in the destination folder. It also includes package.json for the tested project.
RunJestWhenDonePluginruns jest when webpack is done. It runs jest from the destination folder so jest uses the webpack transformed files. This lets jest determine what files changed and which runs to test again instead of testing all the files again.
This way of integrating jest and webpack is fairly transparent, requiring little modification to a webpack project. Used along with
source-map-support, you can also get source maps.
Thanks to Colch for letting me take over development of a jest-webpack integration as the jest-webpack npm package.