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Writing unit tests with Jest or Mocha

In modern JavaScript programming, software development unit testing is a process where JavaScript software web developers determine whether a JavaScript program can perform tasks according to multiple single units of source code, such as functions or methods. Jest and Mocha are two of the most popular JavaScript testing framework choices that can help web developers do this.

So, let’s now look at both Jest and Mocha in JavaScript programming and how to write unit tests.

Jest JavaScript Testing Framework.

Jest is a popular JavaScript application testing framework. Jest testing framework is developed by Meta Facebook company. Jest testing framework is especially popular for React development application testing. Jest framework itself is an all-in-one web app testing framework environment that provides JavaScript app developers with a test runner, assertion library, and mocking features in unit testing.

Setting up the Jest framework for testing.

Before using Jest for web app unit testing, developers must manually install it on their computer. If the developer is working on a Node.js or JavaScript project, developers can install it via npm.

Jest framework install syntax.

npm install –save-dev jest

Developers can perform unit testing by using the jest command or by adding scripts to their package.json file.

{

“scripts”: {

“test”: “jest”

}

}

Writing tests in the Jest unit testing framework.

Performing unit tests in the Jest testing framework generally involves explaining the functionality and ensuring that the program test output expected by the developer is exactly the same as the actual program source code output.

Here is an example of a basic test in the Jest testing framework.

// this is a total.js script file

function total(p, q) {

return p + q;

}

module.exports = total;

// let total.test.js file

const total = require(‘./total’);

test(‘let total of 3 + 4 is equivalent to 7’, () => {

expect(total(3, 4)).toBe(7);

});

Here in this Jest unit testing example.

Here Jest test is used to define a test case condition where user explains the behaviour of a total. For example, adding 3 + 4 to total gives the output of 7.

Here expect is an assertion function and toBe adds both the checks and checks the output in the testing process to test whether the output is exactly equal to the expected value or not.

Common Jest matchers in the Jest unit testing framework.

• toBe(value) – This tests whether a value is equal to the expected value in the Jest testing framework.
• toEqual(value) – This tests whether an object is exactly equal to the expected value in the Jest testing framework.
• toBeTruthy(), toBeFalsy() – This tests whether a value is true or false in the Jest testing framework.
• toBeGreaterThan(number), toBeLessThan(number) – This checks whether a value is larger or smaller than the indicated number in the Jest testing framework.

Running Jest tests in JavaScript programming.

To run Jest testing in JavaScript, the user has to apply the below command.

npm total

Here the Jest testing framework will automatically find and run all the testing files with .total.js suffix in the user project.

Key features of Jest testing framework.

• jest Snapshot testing – Jest testing framework can automatically capture snapshots of React components or any values ​​whenever required, and compare them from time to time to ensure that there are no unexpected changes or modifications.
• jest Mocking – Jest unit testing framework provides users with mock features for functions, modules, and even timers.
• jest code coverage – Jest unit testing framework can create program source code coverage reports, which indicate how much portion of the user program code is covered in testing.

Mocha is a flexible JavaScript Testing Framework.

Mocha unit testing framework is another popular testing framework for JavaScript programming, where Mocha unit testing framework is popular for its flexibility. Unlike Jest unit testing framework, Mocha unit testing framework does not come readymade with any assertion library or mocking framework. Here user developer has to connect it with desired multiple assertion library as per their requirement and user can apply it with other tools like Sinon for mock and spy.

Setting up the Mocha testing framework.

Installing Mocha and Chai for assertions in JavaScript.

npm install –save-dev mocha chai

To run Mocha unit testing, add a script to your package.json.

{

“scripts”: {

“test”: “mocha”

}

}

Creating tests in Mocha unit testing.

Here is a simple Mocha testing for assertions using Chai in JavaScript Mocha.

// let create total.js script

function total(p, q) {

return p + q;

}

module.exports = total;

/ check total.test.js

const total = require(‘./total’);

const { expect } = require(‘chai’);

describe(‘total function s’, () => {

it(‘hare we add 4 + 4 is to equal 8’, () => {

expect(total(4, 4)).to.equal(8);

});

});

Here in the above Mocha testing example.

Here describe is used to group related tests in Mocha testing which is useful to arrange multiple tests based on the capacity or module of the existing test.

Here Mocha defines a single test case with a description and a callback function which contains the assertion.

The expect word is used for assertions, in this condition from Chai, and .to.equal tests the equality in the program.

Chai assertion statement with normal Mocha.

• .to.equal(value) – It checks whether two values ​​are equal in the Chai program testing process in Mocha.
• .to.be.true, .to.be.false – It tests the boolean value in the Chai program testing process in Mocha.
• .to.be.a(‘type’) – It tests the data type of the value in the Chai program testing process in Mocha.
• .to.have.lengthOf(number) – Tests the length of an array or string in the Chai program testing process in Mocha.

Running Mocha Testing in JavaScript.

Apply the below command to run Mocha testing in your program.

npm test

Here Mocha testing framework will find all the files with .total.js extension and run them.

Features of Mocha Unit Testing Framework.

• Flexibility – Mocha testing framework does not enforce any strict structure or assertion library, due to which users can use any tool as per their requirement.
• Asynchronous Testing – Mocha testing framework provides great support for asynchronous testing, which uses callbacks or promises to manage asynchronous program operation.
• Hooks – Mocha testing framework provides before, after, beforeeach, beforeeach features hooks to set and remove conditions for testing.

Choose Jest vs Mocha Which testing framework to choose?

Choose Jest testing framework if.

• If JavaScript developers are using React Framework library or other modern JavaScript frameworks.
• If developers want an all-in-one solution test runner, assertion library, mocking, features with minimal configuration.
• If developers need snapshot testing or built-in code coverage in Jest testing framework.

Choose Mocha testing framework if.

• If JavaScript developers need flexibility in setup in their testing, or users want to manually select specific libraries for assertions and mocks.
• Where developers are using a Node.js environment, or need more granular control over test execution.
• Additionally, developers are able to setup and integrate tools such as Chai and Sinon into their own testing frameworks.

major Differences Between Jest and Mocha javascript testing framework

Summary of Jest and Mocha testing frameworks in JavaScript.

In JavaScript programming, Jest and Mocha are both popular choices for creating unit tests in JavaScript. While the Jest testing framework is an all-in-one testing solution that comes pre-built with every element a developer needs, the Mocha unit testing framework offers more flexibility and customization features, allowing developers to choose the custom libraries and tools they desire.

If JavaScript users want a simple, no-configuration JavaScript unit testing framework, especially for React development framework apps, the Jest framework is an ideal environment.

If web JavaScript developers want more flexibility and control in their testing framework setup, or if developers are already using Chai and Sinon, then Mocha testing is a great framework option.