Jest vs Mocha: What’s the Difference?
Tags: javascript, testing
Published: 2022-12-29 16:31:07

Jest and Mocha have both become popular testing frameworks among JavaScript developers. Both are open-source test libraries used to validate code in software applications. Both may be used to run JavaScript code tests. However, a closer examination reveals some distinctions between these two testing systems. This article covers the benefits and drawbacks of Jest vs Mocha, enabling you to choose the best one for your project.

## What are Unit Tests?

Unit testing is a type of software testing in which individual components are tested. The goal is to ensure that each unit of code operates as planned. Therefore, developers perform unit testing throughout an application's development (code phase). It's a good idea to test each program component before going on to the next step. Unit testing is helpful since it’s simple to use and runs rapidly.

Unit testing is an essential component of Test-Driven Development (TDD), which is the practice of describing a function's intended behaviors and what we want it to accomplish (or not accomplish) before we begin work on the actual function. Taking this approach to software development serves several purposes:

- This technique can assist in identifying edge-case possibilities and ensuring that your code continues to work normally in these circumstances.
- It can assist in defining a route to success by specifying the tasks that must be completed during the function.
- As the codebase grows and evolves, this approach insures that modifications to other areas of the codebase do not have a detrimental impact on the performance of the tested function.


## Introduction to Jest vs Mocha

### Jest

[Jest](https://jestjs.io/) is a JavaScript testing framework developed by Facebook. It is primarily intended for React-based apps, although it may also be used with Babel, JavaScript, Node, Angular, and Vue. It can also test NestJS, Next.js, and GraphQL. The Jest testing framework ensures the integrity of any JavaScript codebase. It enables you to develop tests with an easy-to-use, familiar, and feature-rich API that returns results rapidly.

#### Characteristics of Jest:

- **Zero configs:** Jest attempts to function on most JavaScript applications without any configuration. This means you can add Jest as a dependency to your project and begin writing your first test with no or minimal changes.
- **Great API:** Jest is well known for having a robust API with many assertion types for various requirements. Aside from that, its excellent documentation should help you get up and running quickly.
- **Snapshots:** Snapshots are essential for front-end testing because they allow you to validate the integrity of massive objects. This means you don't have to create lengthy tests full of assertions to ensure that every attribute on an object is present and of the correct type.
- **Isolated:** When executing tests, isolation is critical. It guarantees that the findings of different tests do not interfere with one another. Jest runs tests in parallel, each in its process. This means they can't interfere with other tests. Jest serves as the orchestrator, collecting findings from all test procedures.
- **Supports snapshot testing:** Snapshot testing is an excellent method for ensuring that your application's user interface does not change unexpectedly between versions.
- **TypeScript support:** It Supports TypeScript via the ts-jest package.
- **Compatibility:** The Jest framework is compatible with Angular, React, NodeJS, VueJS, and other projects that use Babel.
- **Jasmine traits:** Jest is based on Jasmine; therefore, it inherited all of its admirable traits. Although Jest has left Jasmine, its features have been preserved and its functionalities have been improved on.
- **Speed:** It is a highly rapid testing tool. When our test is CPU constrained, it can save us substantial time throughout our test runs. For example, Jest reduced the local test time from 45 minutes to 14 to 15 minutes.
- **Timer mocks:** Jest can be manipulated with time using:


1. `setTimeout`
1. `clearInterval`
1. `setInterval`
1. `clearTimeout`


#### Limitations of Using Jest

- Using auto-mocking features might cause your test suite to run slowly. This is because the more dependencies a module has, the more effort Jest must perform to fake them out and make them behave like actual dependencies to test your code.
- Jest snapshot testing is unsuitable for projects that create large snapshot files with thousands of lines.
- It has fewer tools and support than more established libraries (like Mocha). This might be a drawback for developers who wish to run and debug their tests using an IDE like WebStorm.


### Mocha

[Mocha](https://mochajs.org/) is an open-source JavaScript testing framework that works in the [browser](https://mochajs.org/#running-mocha-in-the-browser) and on Node.js. It has a fairly basic interface and is intended to test [synchronous](https://mochajs.org/#synchronous-code) and [asynchronous](https://mochajs.org/#asynchronous-code) programming.

Mocha serializes tests to provide flexible and accurate reporting while mapping uncaught exceptions to their related test cases. It enables several forms of testing, such as unit, integration, and end-to-end testing. Mocha provides a foundational test framework for developers. It also includes a plethora of assertion, mocking, and spy libraries that must be installed individually. Chai and Sinon are the most popular of these.

#### Characteristics of Mocha

- **Any assertion library is supported:** Mocha reduces testing expenses and speeds up the process by supporting many JavaScript assertion libraries, including Express.js, Should.js, and Chai. This multiple library support makes designing extensive and complicated test cases easier, and if everything works as expected, retesting won’t be necessary.
- **Synchronous and asynchronous testing is supported:** Mocha was developed to strengthen asynchronous testing with features that call the callback once the test is completed. By eliminating the callback, it allows for synchronous testing.
- **Supports both BDD and TDD environments:** Mocha supports both behavior-driven development (BDD) and test-driven development (TDD), making it simple to construct high-quality tests and increase coverage.
- **Supports multiple browsers:** Mocha makes it simple to write test scenarios that execute smoothly across all major web browsers. It may be expanded with plugins, and each Mocha release includes updated JavaScript and CSS builds for various web browsers.
- **Various installation techniques:** Mocha may be installed globally or as a development requirement for the project. It may also be configured to execute test cases directly in a web browser.


#### Limitations of Mocha

- Unlike Jest, which operates as a standalone framework, Mocha requires more setup, making it weaker.
- An assertion library must be specifically selected if not flexible enough.


## Jest vs Mocha: A Comprehensive Comparison

The differences between Jest vs Mocha may appear minor at first look, but a few aspects must be considered.

First, Jest was designed to function as a standalone testing framework that does not require further dependencies. Mocha, on the other hand, involves merging some libraries to work effectively. As a result, a developer must define which assertion, mocking, or libraries will be used in the project.

Furthermore, Mocha does not specify any complex prerequisites for linking these libraries together, and is known as a more efficient tool that results in speedier test execution. Again, because Mocha does not impose strict requirements for configuring these libraries, it is a better-optimized tool that may be used more readily and efficiently than similar tools.

Also, Jest has fewer features than Mocha and does not support several essential aspects, such as asynchronous testing. Nevertheless, one of its most enticing aspects is its simplicity. Jest may be a better alternative when a lightweight, uncomplicated testing solution is needed.

Jest is also speedier than Mocha. This is because it has snapshot testing capabilities, which implies that tests are executed automatically whenever the code is changed. This makes it simple to keep tests up to date while working.

Mocha provides more functionality because it is a more developed product with a larger community of contributors.

Let’s take a quick look at this chart:

<figure><img src="https://d37oebn0w9ir6a.cloudfront.net/account_32099/image1_a4c956a3d3eedb4130bea9c86b82fdbc.png" alt="Yearly downloads of Jest vs Mocha."/></figure>

Above, the trends of both npm modules are shown over time. However, Jest has a far stronger position, with weekly downloads nearly double that of Mocha's. On the other hand, Mocha is marketed as a more reliable and compact solution with fewer issues.

## Which Framework to Use

The fact that Jest comes packaged with a slew of utilities that may or may not be required for work is a turn-off for some people (think about snapshot testing for a backend project). However, for others, having everything in one location without having to go elsewhere for other tools is ideal.

Also, the majority appears to feel that large backend projects can benefit more often from Mocha's flexibility in terms of setup and ad-hoc external library selection. Furthermore, suppose the high speed of running tests is essential. In this case, Mocha's flexibility is considered carefully against the better rate of the Jest runner.

For front-end development, there is general agreement that, while Mocha does an excellent job, aligning with the framework creators' tools is probably a better idea. It can guarantee better and faster updates when new framework releases are made due to better integration with framework-specific tools. React-Testing-Library is a solid illustration of why Jest would be preferable to Mocha in a React project.

Mocha is arguably the best solution if you have a huge project that requires flexibility and customization. Jest is the best alternative if you have a smaller project and don't require the extra setup and configuration upfront. Which framework will be the best answer for you and your team is entirely up to you.

## Conclusion

In this article, we ran through a brief breakdown and evaluation of the Jest vs Mocha frameworks in order to assist you in choosing the best one for your project needs. Visit [Mocha](https://mochajs.org/) or [Jest](https://jestjs.io/) to learn more about them.