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‎README.md‎

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🃏 Delightful JavaScript Testing
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- **👩🏻‍💻 Easy Setup**: Jest is a complete and easy to set up JavaScript testing solution. In fact, Jest works out of the box for any React project.
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- **👩🏻‍💻 Easy Setup**: Complete and easy to set-up JavaScript testing solution. Works out of the box for any React project.
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- **🏃🏽 Instant Feedback**: Failed tests run first. Fast interactive mode can switch between running all tests or only test files related to changed files.
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- **🏃🏽 Instant Feedback**: Fast interactive watch mode runs only test files related to changed files and is optimized to give signal quickly.
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- **📸 Snapshot Testing**: Jest can [capture snapshots](http://facebook.github.io/jest/docs/en/snapshot-testing.html) of React trees or other serializable values to simplify testing.
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- **📸 Snapshot Testing**: Capture snapshots of React trees or other serializable values to simplify testing and to analyze how state changes over time.
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## Getting Started
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<!-- generated_getting_started_start -->
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Install Jest using `npm`:
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Install Jest using [`npm`](https://www.npmjs.com/):
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```
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npm install --save-dev jest
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```
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Let's get started by writing a test for a hypothetical function that adds two numbers. First, create a `sum.js` file:
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Or via [`yarn`](https://yarnpkg.com/en/package/jest):
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```
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yarn add --dev jest
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```
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Let's get started by writing a test for a hypothetical function that adds two
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numbers. First, create a `sum.js` file:
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```javascript
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function sum(a, b) {
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**You just successfully wrote your first test using Jest!**
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This test used `expect` and `toBe` to test that two values were exactly identical. To learn about the other things that Jest can test, see [Using Matchers](https://facebook.github.io/jest/docs/en/using-matchers.html).
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This test used `expect` and `toBe` to test that two values were exactly
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identical. To learn about the other things that Jest can test, see
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[Using Matchers](UsingMatchers.md).
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## Running from command line
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You can run Jest directly from the CLI (if it's globally available in your `PATH`, e.g. by `npm install -g jest`) with variety of useful options.
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You can run Jest directly from the CLI (if it's globally available in your
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`PATH`, e.g. by `npm install -g jest`) with variety of useful options.
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Here's how to run Jest on files matching `my-test`, using `config.json` as a configuration file and display a native OS notification after the run:
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Here's how to run Jest on files matching `my-test`, using `config.json` as a
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configuration file and display a native OS notification after the run:
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```bash
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jest my-test --notify --config=config.json
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```
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If you'd like to learn more about running `jest` through the command line, take a look at the [Jest CLI Options](https://facebook.github.io/jest/docs/en/cli.html) page.
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If you'd like to learn more about running `jest` through the command line, take
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a look at the [Jest CLI Options](CLI.md) page.
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## Additional Configuration
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### Using Babel
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To use [Babel](http://babeljs.io/), install the `babel-jest` and `regenerator-runtime` packages:
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To use [Babel](http://babeljs.io/), install the `babel-jest` and
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`regenerator-runtime` packages:
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```
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npm install --save-dev jest babel-jest regenerator-runtime
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npm install --save-dev babel-jest babel-core regenerator-runtime
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```
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*Note: Explicitly installing `regenerator-runtime` is not needed if you use `npm` 3 or 4 or Yarn*
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> Note: If you are using a babel version 7 then you need to install `babel-jest`
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> with the following command:
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>
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> ```
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> npm install --save-dev babel-jest 'babel-core@^7.0.0-0' @babel/core regenerator-runtime
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> ```
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_Note: Explicitly installing `regenerator-runtime` is not needed if you use
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`npm` 3 or 4 or Yarn_
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Don't forget to add a [`.babelrc`](https://babeljs.io/docs/usage/babelrc/) file in your project's root folder. For example, if you are using ES6 and [React.js](https://facebook.github.io/react/) with the [`babel-preset-es2015`](https://babeljs.io/docs/plugins/preset-es2015/) and [`babel-preset-react`](https://babeljs.io/docs/plugins/preset-react/) presets:
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Don't forget to add a [`.babelrc`](https://babeljs.io/docs/usage/babelrc/) file
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in your project's root folder. For example, if you are using ES6 and
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[React.js](https://facebook.github.io/react/) with the
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[`babel-preset-es2015`](https://babeljs.io/docs/plugins/preset-es2015/) and
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[`babel-preset-react`](https://babeljs.io/docs/plugins/preset-react/) presets:
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```json
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{
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You are now set up to use all ES6 features and React specific syntax.
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> Note: If you are using a more complicated Babel configuration, using Babel's `env` option,
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keep in mind that Jest will automatically define `NODE_ENV` as `test`.
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It will not use `development` section like Babel does by default when no `NODE_ENV` is set.
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> Note: If you are using a more complicated Babel configuration, using Babel's
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> `env` option, keep in mind that Jest will automatically define `NODE_ENV` as
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> `test`. It will not use `development` section like Babel does by default when
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> no `NODE_ENV` is set.
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> Note: If you've turned off transpilation of ES2015 modules with the option
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> `{ "modules": false }`, you have to make sure to turn this on in your test
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> environment.
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```json
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{
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"presets": [["es2015", {"modules": false}], "react"],
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"env": {
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"test": {
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"presets": [["es2015"], "react"]
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}
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}
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}
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```
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> Note: `babel-jest` is automatically installed when installing Jest and will automatically transform files if a babel configuration exists in your project. To avoid this behavior, you can explicitly reset the `transform` configuration option:
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> Note: `babel-jest` is automatically installed when installing Jest and will
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> automatically transform files if a babel configuration exists in your project.
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> To avoid this behavior, you can explicitly reset the `transform` configuration
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> option:
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```json
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// package.json
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### Using webpack
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Jest can be used in projects that use [webpack](https://webpack.github.io/) to manage assets, styles, and compilation. webpack does offer some unique challenges over other tools. Refer to the [webpack guide](https://facebook.github.io/jest/docs/en/webpack.html) to get started.
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Jest can be used in projects that use [webpack](https://webpack.github.io/) to
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manage assets, styles, and compilation. webpack does offer some unique
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challenges over other tools. Refer to the [webpack guide](Webpack.md) to get
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started.
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### Using TypeScript
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To use TypeScript in your tests, install the `ts-jest` package and the types for Jest.
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npm install --save-dev jest ts-jest @types/jest
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```
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then modify your `package.json` so the `jest` section looks something like:
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```json
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{
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"jest": {
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"transform": {
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"^.+\\.tsx?$": "ts-jest"
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},
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"testRegex": "(/__tests__/.*|(\\.|/)(test|spec))\\.(jsx?|tsx?)$",
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"moduleFileExtensions": [
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"ts",
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"tsx",
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"js",
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"jsx",
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"json",
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"node"
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]
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}
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}
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```
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To use TypeScript in your tests you can use
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[ts-jest](https://github.com/kulshekhar/ts-jest).
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<!-- generated_getting_started_end -->
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## Documentation

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