README
jest-webpack
A helper tool and webpack plugin to integrate jest
and webpack
.
Add it to your project as a developer dependency. And run it like webpack
or webpack-dev-server
from the command line or as a package.json
script.
Install
npm install --save-dev jest-webpack
or with yarn
yarn add -D jest-webpack
Update package.json
Add it as a package.json
script
{
"name": "my-package",
"scripts": {
"test": "jest-webpack"
Run it
npm test
Run it with jest options
npm test -- --testPathPattern test-just-this-file
Status
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.
- The
TestEntriesPlugin
finds test files that jest will operate on and creates entry chunks for them. - The
EntryReferencePlugin
creates 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 bothcss-loader
andcss-loader/locals
for 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. - The
EmitChangedAssetsPlugin
removes entry chunks that already exist in the destination folder. It also includes package.json for the tested project. - The
RunJestWhenDonePlugin
runs 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.
Special Thanks
Thanks to Colch for letting me take over development of a jest-webpack integration as the jest-webpack npm package.