Babel-jest is a Jest plugin that uses Babel to transform JavaScript code. It enables developers to write tests in latest JavaScript syntax by automatically compiling the code using Babel. Babel-Jest ensures your test code base is in sync with modern JavaScript standards and practices while benefiting from Jest's robust testing capabilities.
To use babel-jest, if you already have jest-cli installed, all you need to do is add babel-jest and it will automatically compile your JavaScript code using Babel. You can add the package to your project by running the following command in your terminal:
yarn add --dev babel-jest @babel/core
If you wish to write your own preprocessor, you would need to uninstall and delete babel-jest, and then set the config.transform option to your preprocessor.
For instances where you are using babel-jest with additional code preprocessors, an explicit setup is required. In such cases, you need to define babel-jest as a transformer for your JavaScript code by mapping .js files to the babel-jest module. This also applies to Typescript files. The definition is done in your configuration file like this:
"transform": {
"\\.[jt]sx?$": "babel-jest"
},
You can find the babel-jest documentation on the Jest official website at https://jestjs.io/docs/configuration. These docs provide a comprehensive guide on how to install, use, and configure babel-jest, among other useful information for developers. The link to the babel-jest GitHub repository is git+https://github.com/jestjs/jest.git, where you can also find insights on the module usage as well as code examples.
