Jest vs Mocha: Comparing NodeJS Unit Testing Frameworks

JavaScript or JS is the most popular programming language widely used as a scripting language for web pages. It’s also used in non-browser environments such as Node.js, Apache CouchDB, and Adobe Acrobat. It has been around for almost two decades, and it continues to be used by millions of people, especially developers all around the world.

Source

As per the Stack Overflow survey 2021, JS is the most popular language among programming, markup, and scripting languages. It continues to be one in 2022 too.

When it comes to JavaScript testing, various JS testing frameworks are available to test your features at scale. Below are some of the testing frameworks available, which are ranked as per the “usage” rankings through the years.

In this article, we will be comparing two popular testing frameworks – Jest and Mocha – and help you decide which one to get started with for Unit testing in NodeJS.

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 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.

Let’s begin this article by introducing the two testing tools that are popularly used for NodeJS.

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

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

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 graph below also shows the most recent trends of both npm packages compared against each other. It’s clear that Jest has a way stronger position and almost doubles mocha’s weekly downloads. On the other hand, the number of issues encountered in Mocha is far less than that in Jest. The choice is yours!

Source

Jest vs Mocha: Basic Unit Test Case Designing

Let’s 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 their own advantages and limitations, which means choosing between them is subjective to the projects they will be used for as well as a pinch of personal preference.

• Large back-end projects can benefit more from the flexibility of Mocha in terms of configuration and ad-hoc external library choice. 
• If the speed of test running is of the sole importance, the superior speed of the Jest runner will be suitable. 

Similarly, if the goal is getting started fast with some tests on a small project, Jest’s no-setup-needed approach can be a winner. Overall, there seems to be a lot of love out there for both Mocha and Jest.

In 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