Jest Testing Tutorial: An Introductory Guide For Beginners

Introduction

Do you wish to write tests for your code independently? If so, then you’ve landed in the right place. In this comprehensive Jest testing tutorial, we’ll help you learn and do it in one of the fastest ways; yes, it’s Jest Testing.

Designed for unit testing JavaScript and React code, Jest is compatible with projects using aBbel, TypeScript, Node, Angular, Vue, and more. Jest requires zero configuration, allows Snapshot Testing, and runs parallel tests in a sandboxed environment."

With Jest unit testing, you can write reliable and maintainable tests for your applications. Jest’s powerful mocking capabilities allow you to isolate the code you are testing, ensuring that your tests run consistently. It also provides a rich API for creating test suites, including support for asynchronous tests, making it ideal for modern JavaScript applications for which you should learn JavaScript too.

Additionally, Jest’s CLI offers a simple and intuitive way to run your tests and generate detailed reports. The framework also includes features like code coverage analysis and integration with various CI/CD pipelines, helping you maintain high code quality and ensure that your application works as expected.

Looks like you are finding this interesting 

Well, this is just the start! Today, we will guide you through the essentials of Jest unit testing. From installation and configuration to writing and executing your first tests, this jest tutorial covers the basics to advance concepts of jest testing. We will talk about what is Jest framework, its main characteristics and features, and a detailed approach to starting with the Jest test as a beginner. In the later part, we talk about the salaries of developers with Jest testing competencies. So, stay tuned with us through to the end

Let’s start with understanding what is Jest, as a framework.

What is Jest Framework?

Jest is one of the leading frameworks for unit testing in JavaScript. It was created by Facebook (now “Meta”) for their internal testing for React components in 2011. Later, in 2014, Meta released Jest as an open-source testing framework. 

Soon after its public release, Jest became popular among developers for the advantages it offers. The popularity of Jest is well defined by the huge download numbers and its use in public repositories. There were around 300+ million Jest downloads in the last month and used over 11,000,000 public repositories on GitHub.  

Though created for unit testing React components, jest is used for testing both front-end and back-end JavaScript applications. It’s a framework, which means it provides a complete setup for testing rather than just individual pieces. 

Let’s now move on to exploring the main characteristics of Jest in the next section.

Main characteristics of Jest

Jest testing is popular for many reasons. These are the characteristics that make it unique and user-friendly. Here’s a brief explanation of the key characteristics of the Jest testing framework.

1. Zero Configuration: Setting up Jest is easy and fast. It assumes sensible defaults, saving considerable time in tweaking configuration and reading lengthy documents. When you create a new project and install Jest (via npm or yarn), it’s ready to roll. You write your tests, run npm jest, and Jest handles the rest.

2. Command Line Interface: Jest includes a Command Line Interface (CLI) that allows you to run commands directly from the terminal. It also includes an assertion library to check if the conditions in your tests are met.  

3. Built-in Code Coverage: The built-in code coverage shows you reports of what files are not covered in your code, making Jest extremely handy when writing tests and helping you to ensure everything is covered.

4. Snapshot Testing: Snapshot Testing allows you to capture the output of components and compare them to previous outputs.

5. Mocks and Spies: The built-in Mocking library allows you to mock any object outside your test scope and spy on function calls.

6. Sandboxed Parallel Testing: Jest executes all tests in an isolated environment, allowing you to run multiple parallel tests. 

7. Great API: Jest offers a well-segregated toolkit to help you fetch and use while testing. These include various “matchers” that you may need to get returns. All you need is to land on the documentation page on the Jest official website and explore the API section.

How to get started with testing using Jest

Testing using Jest is straightforward, especially with its minimal configuration requirements. Let’s see how to get started with Jest testing in a step-by-step chronology below.

Step 1: Install Node.js and npm

Before you begin,  you do need to have node.js installed so we can use npm. If you do not have one, please download it from  Node.js official website. Once you have node installed you can check the version by typing:

$node-v

This will give you the version of the node you installed.

Step 2: Set Up Your Project

Initialize npm: 

Before we move on to installing Jest. we need to initiate npm first. To do that simply type:

$ npm init -y

This will create a package.jason. Currently, we have no dependencies whatsoever. Let’s move on to installing Jest with dev dependencies.

Step 3: Install Jest

Install Jest as a development dependency in your project. Jest as dev dependency is important as we run tests only during developments. 

npm install --save-dev jest

If you open package.jason, you will see Jest under dev dependency. 

Step 4: Configure Jest

Add a test script to your package.json file to run Jest. Initially, you will have some different scripts there. Replace the texts after the test with “Jest.” That’s the only configuration you need to do with Jest Testing Framework. Doing this will define our test script.

{

  "scripts": {

    "test": "jest"

  }

}

Now let’s move to writing your first.

Step 5: Write Your First Test

Create a test file: Jest will look for files with .test.js or .spec.js extensions by default. Create a file named sum.test.js.

touch sum.test.js

Write a simple test:

// sum.js

function sum(a, b) {

  return a + b;

}

module.exports = sum;

Module. exports will help export your code to Jest for testing. The next step would be Importing the test. This can be done as shown below.

// sum.test.js

const sum = require('./sum');

test('adds 1 + 2 to equal 3', () => {

  expect(sum(1, 2)).toBe(3);

});

Step 6: Run Your Tests

Run the tests using the following command:

npm test

Jest will run all test files and output the results in the terminal. You can see the result as “Passed.” Or if it does not pass there would be reasons displayed.

Why use Jest Framework For Selenium JavaScript Testing?

Automation testing is essential to ensure a seamless user experience in web applications. Selenium, a popular open-source testing framework, is crucial in verifying products across different browsers and operating systems. Using Jest for selenium Javascript testing can give the following advantages:

1. Browser Rendering Validation:

Jest isn’t just for unit tests but also for validating browser rendering. You can use it to ensure that your web applications render correctly across different browsers. Jest’s coverage reporting helps you understand which parts of your code are well-tested and which need attention. Well-tested code gives you confidence during refactoring and feature development.

2. Ease of Setup and Configuration

Jest works out of the box without requiring extensive setup. This makes it straightforward to integrate with existing projects. Configuring Jest is simple and can be easily customized if needed. 

3. Jest Powerful Features

Although typically used for React components, snapshot testing can also be useful in verifying the UI state at different points in your Selenium tests. Jest’s powerful mocking capabilities allow you to simulate various states and behaviors of your application, making it easier to isolate and test individual components.

4. Test Runner and Assertion

Jest comes with a built-in test runner, eliminating the need for additional tools to execute your tests. It provides a comprehensive set of “matchers” to assert different conditions, which are more readable and expressive than those in many other frameworks.

5. Parallel Test Execution

Jest runs tests in parallel, speeding up the execution of your test suite. This is particularly beneficial for large test suites.  Each test file is run in its own sandbox environment, preventing side effects between tests and ensuring more reliable results.

6. Built-in Code Coverage

Jest automatically generates code coverage reports and provides insights into which parts of your code are tested and which are not.

7. Watch Mode

Jest’s watch mode re-runs tests related to changed files and provides immediate feedback during development and enhancing productivity.

8. Community and Ecosystem

Jest has a large and active community that ensures continuous improvement and support. It integrates well with other popular tools and libraries in the JavaScript ecosystem, such as Babel, Webpack, and ESLint.

Some Basics on writing tests with Jest

Using Jest efficiently requires understanding the Jest ecosystem thoroughly. Beginners should start with understanding the implementation and use of the basic jest terminologies. Let’s take a look at some of the most often-used basics among them.

1. Test Suite: A group of related tests. In Jest, you can create a test suite using the describe function.
2. Test Case: An individual test. Test cases are written using the test or it function.
3. Assertions: Assertions are used to check whether the expected outcome matches the actual outcome. Jest provides a variety of built-in matchers for assertions.

Key Functions:

•  test and it

Both test and it are used to define individual test cases.  

test('description', () => {

  // test implementation

});

// or

it('description', () => {

  // test implementation

});

• describe

Use describe to group related tests together.

describe('sum module', () => {

  test('adds 1 + 2 to equal 3', () => {

    expect(sum(1, 2)).toBe(3);

  });

  test('adds 2 + 2 to equal 4', () => {

    expect(sum(2, 2)).toBe(4);

  });

});

Basic Matchers:

• toBe

expect(value).toBe(expectedValue);

expect(value).toEqual(expectedValue); // for objects and arrays

• Truthy/Falsy Matchers:

expect(value).toBeTruthy();

expect(value).toBeFalsy();

• Numbers:

expect(value).toBeGreaterThan(number);

expect(value).toBeLessThan(number);

• Strings:

expect(string).toMatch(/regex/);

• Arrays and Iterables:

expect(array).toContain(item);

• Exceptions:

expect(() => { throw new Error('error'); }).toThrow('error');

• Mock Functions:

const myMock = jest.fn();

myMock();

expect(myMock).toHaveBeenCalled();

• Mock Implementation:

const myMock = jest.fn().mockImplementation(() => 'mocked value');

expect(myMock()).toBe('mocked value');

• Mock Modules:

jest.mock('module-name');

Asynchronous Testing

• Callbacks:

test('async callback', done => {

  function callback(data) {

    expect(data).toBe('value');

    done();

  }

  asyncFunction(callback);

});

• Promises:

test('async promises', () => {

  return asyncFunction().then(data => {

    expect(data).toBe('value');

  });

});

• async/await:

test('async/await', async () => {

  const data = await asyncFunction();

  expect(data).toBe('value');

});

Features of Jest

Besides the main characteristics that we discussed in this article, Jest comes with unique features that help users ensure efficient and effective code testing. This includes:

• Interactive Watch Mode: Jest has a watch mode that re-runs tests related to changed files, providing instant feedback and improving the developer experience.
• Comprehensive Docs: Jest has thorough and well-organized documentation, which is a valuable resource for both beginners and experienced developers.
• TypeScript Integration: Jest supports TypeScript out of the box with minimal configuration, allowing you to write tests for TypeScript projects seamlessly.
• React Integration: While Jest is popular for testing React components, it can be used for testing other JavaScript frameworks and libraries as well.
• Extendable: Jest’s plugin system allows you to extend its functionality with additional plugins and integrations.
• Fast and Efficient: Jest’s parallel test execution and intelligent test selection make it fast and efficient, even for large test suites.
• Integration with Babel, Webpack, and More: Jest integrates seamlessly with other tools in the JavaScript ecosystem, such as Babel for transpiling ES6+ code and Webpack for bundling.

Salary with jest framework

Let’s dive into the world of salaries for JavaScript developers in the United States, with a special focus on those who work with Jest. 

Average JavaScript Developer Salary:

As of June 27, 2024, the average JavaScript Developer salary in the United States is approximately $104,948 per year. (Source: Salary)

However, salary ranges can vary based on factors like education, certifications, additional skills, and years of experience.

Hourly Rate:

Zip recruiter mentions the hourly wage for the average JavaScript Developer with Jest to be around $51.24 per hour.

While Jest is a popular testing framework, it’s essential to note that JavaScript developers work on various aspects of web development beyond testing. For example, React.js developers (who often use Jest for testing) have an average yearly salary of around $92,0003.

Salaries can significantly differ based on the location (cities with higher living costs tend to offer higher salaries) and the specific industry. Please be informed that the demand for skilled JavaScript developers remains strong, especially as web applications continue to evolve.

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Conclusion

Testing applications for efficiency and accuracy is a crucial part of the development process. It’s a continuous process and usually consumes a considerable time. Further test records can serve as references for future developments. As such, a software testing framework that allows parallel tests to run in isolated environments while being fast and secure is a mandatory need. Jest testing framework can be an ideal choice for developers at all levels. 

With step-by-step guidance for starting with jest testing, we hope you find this jest tutorial helpful. Still, having some doubts? Drop us a query in the comment section, and we would be more than happy to answer you back. You can also explore and enroll in our QA software testing courses to fast-track your testing career, and we’ll help you land the job you always wanted.

FAQs

Q1. What is Jest?

Jest is a JavaScript testing framework maintained by Facebook. It is widely used for testing JavaScript applications, particularly those built with React. Jest provides a simple and intuitive API for writing tests and comes with built-in tools for assertions, mocking, and code coverage.

Q2. How do I install Jest?

You can install Jest using npm or yarn. Run the following command in your project directory:

npm install --save-dev jest

# or

yarn add --dev jest

Q3. How do I run Jest tests?

You can run Jest tests by adding a test script to your package.json file and executing it. Add the following script:

"scripts": {

  "test": "jest"

}

Then run your tests with:

npm test

# or

yarn test

Q4. What are matchers in Jest?

Matchers are methods used to check the values in your tests.

For example, toBe is a matcher that checks if a value is equal to a specified value. Other common matchers include toEqual, toContain, toBeTruthy, and toHaveBeenCalled.