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Node.js Unit Testing:

Unit Testing in Node.js:

In Node.js, each component of the system needs to be tested alone in order to ensure that it is reliable and correct.

Here is how to write and run unit tests using popular testing frameworks such as Mocha and Jest, with assertion libraries like Chai.

Writing and Running Unit Tests:

Mocha and Chai:

JavaScript has a test framework called Mocha which is highly flexible and feature-rich. Chai pairs well with Mocha as an assertion library for human-readable assertions.

Installation:

                                    
                                    npm install --save-dev mocha chai

Example Application:

write a simple function to test. Create a file 'math.js':

                                    
// math.js
function add(a, b) {
    return a + b;
}

function subtract(a, b) {
    return a - b;
}

module.exports = { add, subtract };

Writing Tests:

Create a directory named test and a file math.test.js inside it:

                                    
// test/math.test.js
const { expect } = require('chai');
const { add, subtract } = require('../math');

describe('Math functions', () => {
    describe('add()', () => {
        it('should add two numbers correctly', () => {
            expect(add(2, 3)).to.equal(5);
            expect(add(-1, -1)).to.equal(-2);
        });
    });

    describe('subtract()', () => {
        it('should subtract two numbers correctly', () => {
            expect(subtract(5, 3)).to.equal(2);
            expect(subtract(-1, -1)).to.equal(0);
        });
    });
});

Running Tests::

Add a test script to your 'package.json':

                                    
"scripts": {
    "test": "mocha"
}

Run the tests:

                                    
                                    npm test

Jest:

Jest is a delightful JavaScript testing framework with a focus on simplicity.

Installation:

                                    
                                    npm install --save-dev jest

Example Application:

You can use the same math.js file from the previous example.

Writing Tests:

Create a directory named __tests__ and a file math.test.js inside it:

                                    
// __tests__/math.test.js
const { add, subtract } = require('../math');

test('adds 2 + 3 to equal 5', () => {
    expect(add(2, 3)).toBe(5);
});

test('adds -1 + -1 to equal -2', () => {
    expect(add(-1, -1)).toBe(-2);
});

test('subtracts 5 - 3 to equal 2', () => {
    expect(subtract(5, 3)).toBe(2);
});

test('subtracts -1 - -1 to equal 0', () => {
    expect(subtract(-1, -1)).toBe(0);
});

Running Tests:

Add a test script to your package.json:

                                    
"scripts": {
    "test": "jest"
}

Run the tests:

                                    
                                    npm test

Key Differences Between Mocha and Jest:

Configuration:

Mocha: Needs more setup typically used with additional libraries like Chai for assertions or Sinon for mocks.
Jest: This comes with batteries included providing built-in assertions, mocks and spies.

Ease of Use:

Mocha: It can be widely customized because it is very flexible.
Jest: In many use cases are easy to set up with zero configuration required.

Features:

Mocha: There are extra libraries needed for extended functionalities.
Jest: Has snapshot testing, coverage reports, and a powerful mocking library out-of-the-box.