Jest
๐ Delightful JavaScript Testing
-
๐ฉ๐ปโ๐ป Easy Setup: Complete and easy to set-up JavaScript testing solution. Works out of the box for any React project.
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๐๐ฝ 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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๐ธ Snapshot Testing: Capture snapshots of React trees or other serializable values to simplify testing and to analyze how state changes over time.
Getting Started
Install Jest using yarn
:
yarn add --dev jest
Or via npm
:
npm install --save-dev jest
The minimum supported Node version is v6.0.0
by default. If you need to
support Node 4, refer to the
Compatibility issues
section.
Let's get started by writing a test for a hypothetical function that adds two
numbers. First, create a sum.js
file:
function sum(a, b) {
return a + b;
}
module.exports = sum;
Then, create a file named sum.test.js
. This will contain our actual test:
const sum = require('./sum');
test('adds 1 + 2 to equal 3', () => {
expect(sum(1, 2)).toBe(3);
});
Add the following section to your package.json
:
{
"scripts": {
"test": "jest"
}
}
Finally, run yarn test
and Jest will print this message:
PASS ./sum.test.js
โ adds 1 + 2 to equal 3 (5ms)
You just successfully wrote your first test using Jest!
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.
Running from command line
You can run Jest directly from the CLI (if it's globally available in your
PATH
, e.g. by yarn global add jest
) with variety of useful options.
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:
jest my-test --notify --config=config.json
If you'd like to learn more about running jest
through the command line, take
a look at the Jest CLI Options
page.
Additional Configuration
Using Babel
Babel is automatically handled by Jest using babel-jest
.
You don't need install anything extra for using Babel.
Note: If you are using a babel version 7 then you need to install
babel-core@^7.0.0-0
and@babel/core
with the following command:yarn add --dev 'babel-core@^7.0.0-0' @babel/core
Don't forget to add a .babelrc
file
in your project's root folder. For example, if you are using ES6 and
React.js with the
babel-preset-env
and
babel-preset-react
presets:
{
"presets": ["env", "react"]
}
You are now set up to use all ES6 features and React specific syntax.
Note: If you are using a more complicated Babel configuration, using Babel's
env
option, keep in mind that Jest will automatically defineNODE_ENV
astest
. It will not usedevelopment
section like Babel does by default when noNODE_ENV
is set.
Note: If you've turned off transpilation of ES modules with the option
{ "modules": false }
, you have to make sure to turn this on in your test environment.
{
"presets": [["env", {"modules": false}], "react"],
"env": {
"test": {
"presets": [["env"], "react"]
}
}
}
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 thetransform
configuration option:
// package.json
{
"jest": {
"transform": {}
}
}
Using webpack
Jest can be used in projects that use webpack to manage assets, styles, and compilation. webpack does offer some unique challenges over other tools. Refer to the webpack guide to get started.
Using TypeScript
To use TypeScript in your tests you can use ts-jest.
Documentation
Learn more about using Jest on the official site!
Badge
Show the world you're using Jest โ
[![tested with jest](https://img.shields.io/badge/tested_with-jest-99424f.svg)](https://github.com/facebook/jest)
[![jest](https://facebook.github.io/jest/img/jest-badge.svg)](https://github.com/facebook/jest)
Contributing
Send issues and pull requests with your ideas. For more information about contributing PRs and issues, see our Contribution Guidelines.
Good First Issue is a great starting point for PRs.