Jest vs Mocha: Comparing NodeJS Unit Testing Frameworks

Jest and Mocha are two popular JavaScript testing frameworks, but they cater to different needs. Jest is an all-in-one testing solution with built-in assertions, mocking, and snapshot testing, making it ideal for React and front-end projects.

Mocha, on the other hand, is a flexible and lightweight framework that requires additional libraries for assertions and mocking, making it great for custom setups and back-end testing.

This comparison guide breaks down their differences to help you choose the right tool for your project.

What is Unit Testing?

Unit testing is a software testing technique in which the smallest testable parts of an application, called Units, are independently and individually tested. This is done during the development phase of an application. It is a WhiteBox testing technique usually performed by software developers. In SDLC, STLC, and V Models, unit testing is the first level of testing done before Integration testing. Unit testing is an integral part of the TDD (Test Driven Development) approach. In this approach, developers write unit tests for the feature even before it is implemented.

Why is Unit Testing needed?

Unit testing is essential for several reasons, including:

• Unit testing helps in improving the code quality.
• It helps in finding bugs early on in the development life cycle.
• It saves cost.
• Debugging processes become easier.
• It also provides an added advantage to the users in the way that they can add any new features without breaking any other part of their application.
• Developers can also reuse the code, migrating it to new projects.

What is Mocha?

Mocha is a JavaScript testing framework that is designed for testing apps running in NodeJS. It supports various types of testing including Unit, Integration, End-to-End, etc. It provides developers with a base test framework. It also provides numerous options of assertion, mocking, and spy libraries which need to be installed separately. The most popular ones are Chai and Sinon.

Mocha can be installed using the required commands:

npm install mocha

Install globally:

npm install --global mocha

Install as a dependency:

npm install -- save-dev mocha

Key Features of Mocha

Mocha is a flexible and feature-rich JavaScript testing framework designed for asynchronous and synchronous testing. It provides a modular approach, making it a popular choice for unit and integration testing. Some of its key features include:

• Flexible & Modular: Works with assertion libraries like Chai for custom test setups.
• Asynchronous Testing: Supports async/await and promises for handling async operations.
• Rich Reporting: Offers multiple built-in reporters for better test insights.
• Hooks Support: Provides before(), beforeEach(), after(), and afterEach() for test setup and teardown.
• Wide Ecosystem: Compatible with various assertion, mocking, and spying libraries.

Advantages of using Mocha for Unit Testing

Mocha is widely used for unit testing in Node.js and backend applications, offering flexibility and powerful asynchronous handling. Here’s why developers prefer it:

• Highly Customizable: Works with various assertion and mocking libraries for tailored testing.
• Better Control Over Testing Setup: Allows structured and organized test cases with hooks.
• Supports Asynchronous Testing: Handles async operations seamlessly using callbacks, promises, or async/await.
• Multiple Reporters: Provides a range of test report formats to fit different needs.
• Broad Community Support: Well-documented and actively maintained with strong community contributions.

Challenges/Limitations of using Mocha for Unit Testing

While Mocha is powerful, it does have some limitations, particularly when compared to all-in-one testing solutions like Jest. Some of its challenges include:

• Lack of Built-in Assertions & Mocks: Requires external libraries like Chai, Sinon, or Jest for assertions and mocking.
• Configuration Overhead: Needs manual setup for testing environments, unlike Jest, which works out of the box.
• Slower Execution in Large Test Suites: Lacks optimizations like parallel test execution, making it slower for extensive test suites.
• No Built-in Snapshot Testing: Unlike Jest, Mocha does not support snapshot testing natively.
• Limited Support for Front-End Testing: More suitable for back-end and Node.js projects rather than React or UI tests.

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What is Jest?

Jest is an open-source JavaScript testing framework developed by Facebook. It was mainly developed for Node, React, Angular, and other JavaScript-based applications. It is one of the top JavaScript testing frameworks for test automation. It not only comes with a test runner but also with its own assertion and mocking library. This means there is no need to install and integrate additional libraries to be able to mock, spy, or make assertions. Test cases can be written just after Jest is installed.

Jest validates almost everything around JavaScript, especially the browser rendering of web applications, making it one of the best Javascript testing frameworks.

Jest can be installed using the required commands:

Install globally:

npm install --global jest

Install as a dependency:

npm install -- save-dev jest

Key Features of Jest

Jest is a powerful JavaScript testing framework designed for simplicity and performance. It comes with built-in features that make testing fast and easy, especially for front-end applications and React projects. Some of its key features include:

• Zero Configuration: Works out of the box with minimal setup.
• Built-in Assertions & Mocks: Includes an assertion library and built-in mocking for dependencies.
• Snapshot Testing: Captures UI snapshots to track changes over time.
• Fast and Parallel Execution: Runs tests in parallel to improve performance.
• Code Coverage Reports: Provides detailed test coverage reports.
• Supports Asynchronous Testing: Easily handles async/await, Promises, and callbacks.

Advantages of using Jest for Unit Testing

Jest is widely preferred for unit testing JavaScript applications, especially in front-end testing strategy. Here’s why:

• All-in-One Framework: Comes with built-in support for assertions, mocking, and test runners.
• Great for React and Front-End Testing: Officially recommended for testing React applications.
• Snapshot Testing: Helps track unintended UI changes easily.
• Faster Execution: Runs tests in parallel and isolates test environments for speed.
• Simple Setup and Configuration: Works with minimal configuration, unlike Mocha.
• Built-in Code Coverage Reports: Provides test coverage reports without extra plugins.

Challenges/Limitations of using Jest for Unit Testing

Despite its advantages, Jest has some limitations, especially for complex backend or custom testing needs:

• Slower for Large Test Suites: Jest’s parallel execution can lead to higher memory consumption.
• Not Ideal for Backend Testing: Mocha or other frameworks are often preferred for Node.js testing.
• Debugging Can Be Tricky: Due to Jest’s test isolation, debugging can sometimes be harder than with Mocha.
• Less Customizable Compared to Mocha: While Jest is easy to use, Mocha provides more flexibility for custom setups.
• Performance Overhead in CI/CD Pipelines: Running Jest tests in large projects can be slower in CI/CD environments.

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Jest vs Mocha: Main Differences

At first glance, the differences between Mocha and Jest seem insignificant. However, there are a few key differences to be noted.

The most basic difference is that Jest is a comprehensive JavaScript testing framework with built-in features like assertions, mocking, and coverage, while Mocha needs additional libraries for these functionalities.

Explore jest vs mocha in detail with this comparison

Jest vs Mocha: Basic Unit Test Case Designing

Consider an example for Unit testing of both the frameworks. Consider a class called Student with two properties: name and age and an instance: isStudent() which checks if the student’s age is above or equal to 4.

Below is the source file for the above example.

// student.js

class Student {
constructor(name, age) {
this.name = name;
this.age = age;
}

isStudent() {
return this.age >= 4;
}
}

module.exports = Student;

Mocha test.js file (with Chai assertion library) will look like this:

// mocha.test.js

const Student = require('./student');

describe('Student unit tests', () => {
let student;

beforeEach(() => {
student = new student('Johny', 5);
});

it('Should be a Student', () => {
expect(student.isStudent()).to.be.true;
});

it('Should not be a Student', () => {
student.age = 2;
expect(student.isAStudent()).to.be.false;
});

// ...
});

Jest test.js file will look like this:

// jest.test.js

const Student = require('./student');

describe('Student unit tests', () => {
let Student;

beforeEach(() => {
Student = new Student('Johny', 5);
});

it('Should be a Student', () => {
expect(Student).toBeDefined();
expect(Student.isStudent()).toBe(true);
});

it('Should not be a Student', () => {
student.age = 2;
expect(Student).toBeDefined();
expect(Student.isStudent()).toBe(false);
});

// ...
});

You can see that both Jest and Mocha have different syntaxes. Describe and expect do not seem to be visually different from each other for both the frameworks but they actually work in a slightly different way.

Also, Mocha is able to handle more modularised code with logical operators like or, and etc whereas in Jest, several assertions are separated into single tasks with a more concise syntax.

Which one is preferred: Jest or Mocha?

Both Mocha and Jest have advantages and limitations. This means that choosing between them is subjective to the projects they will be used for and to personal preference.

Here is an overview of when to use which framework:

Importance of Testing on Real Devices

Running your Jest and Mocha unit tests on real devices helps you verify that your code runs as expected under real user conditions, irrespective of the device, browser, or OS that it runs on.

It can help you identify inconsistencies in performance, integration and user experience in specific devices. This will boost the reliability and accuracy of your tests.

For this purpose, use trustworthy tools like BrowserStack, which offers a real device cloud platform to run your automated tests over 3500+ different devices, browsers, and OS combinations.

Conclusion

Whether you prefer Jest to Mocha for unit testing, BrowserStack is compatible with it along with different automation frameworks such Selenium, Cypress, Playwright, Puppeteer, etc. This will easily facilitate your agile scaling by testing on real browsers and devices, thus accelerating the software development cycle.

Run Unit Tests on BrowserStack Automate