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Setting up Jest in Your JavaScript Project

Learn how to set up Jest testing framework in your JavaScript project with step-by-step instructions.

Includes installation, configuration, and writing your first test.
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Setting up Jest in Your JavaScript Project

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Getting started with testing can feel overwhelming, but I’m here to make it super simple! Today, we’ll walk through setting up Jest, one of the most popular testing frameworks in the JavaScript ecosystem. Trust me, once you get the hang of it, you’ll wonder why you didn’t start testing sooner.

Why Choose Jest?

Before we dive into the setup, let me tell you why Jest is awesome. It’s not just me who thinks so – it’s backed by Facebook and used by companies like Twitter, Airbnb, and Instagram. Jest comes with everything you need right out of the box: a test runner, assertion library, and mocking capabilities. Plus, it’s blazing fast thanks to its parallel test execution.

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Getting Started

Let’s break down the setup process into simple steps:

  1. First, make sure you have a JavaScript project ready with package.json. If not, run:
Terminal window
npm init -y
Now, let's install Jest as a development dependency:
bash
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npm install --save-dev jest
Open your package.json and add this test script:
json
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{
"scripts": {
"test": "jest"
}
}
Writing Your First Test
![Abstract waves of light trails forming interconnected networks fluorescent green and black color palette dynamic motion blur effect captured from a side angle with upward tilt high-quality ultra-realistic cinematic 8K UHD high resolution sharp and detail](/image_generation/tillitsdone_Jest_Basic-topic_topics_find_Setting-up-Jest-in-Your-JavaScript-Projectcontent_1732730530541_2.jpeg "Abstract waves of light trails forming interconnected networks fluorescent green and black color palette dynamic motion blur effect captured from a side angle with upward tilt high-quality ultra-realistic cinematic 8K UHD high resolution sharp and detail")
Let's write a simple test to make sure everything's working. Create a new file called sum.js:
javascript
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function sum(a, b) {
return a + b;
}
module.exports = sum;
Then create a test file called sum.test.js:
javascript
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const sum = require('./sum');
test('adds 1 + 2 to equal 3', () => {
expect(sum(1, 2)).toBe(3);
});
Run your test with:
bash
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npm test
And voilà! You've just written and executed your first Jest test. Pretty straightforward, right?
Best Practices and Tips
Here are some nuggets of wisdom I've learned along the way:
Name your test files with the .test.js or .spec.js suffix
Keep your tests close to the code they're testing
Write descriptive test names that explain the expected behavior
Use Jest's watch mode during development with jest --watch
Remember, testing isn't about achieving 100% coverage from day one. Start small, test the critical parts of your application first, and gradually build up your test suite as you go.
![Macro shot of crystalline structures with intricate patterns sunshine yellow and gray color scheme sharp geometric formations catching light extreme close-up angle with shallow depth of field high-quality ultra-realistic cinematic 8K UHD high resolution sharp and detail](/image_generation/tillitsdone_Jest_Basic-topic_topics_find_Setting-up-Jest-in-Your-JavaScript-Projectcontent_1732730530541_3.jpeg "Macro shot of crystalline structures with intricate patterns sunshine yellow and gray color scheme sharp geometric formations catching light extreme close-up angle with shallow depth of field high-quality ultra-realistic cinematic 8K UHD high resolution sharp and detail")
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