How do you write unit tests in Node.js?

Unit testing in Node.js involves testing individual units or components of code in isolation to ensure they function correctly. This helps identify bugs early in the development process, maintain code quality, and facilitate refactoring. Several testing frameworks and libraries are available for writing unit tests in Node.js, including Mocha, Jest, Jasmine, and Ava.

Here’s a basic example of how to write unit tests using Mocha and Chai:

Install Testing Dependencies:

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npm install mocha chai --save-dev

Write Unit Tests:

• • Create a test file (e.g., calculator.test.js) containing your unit tests.

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const { expect } = require('chai');

const { add, subtract } = require('./calculator');




describe('Calculator', () => {

 it('should add two numbers', () => {

 expect(add(2, 3)).to.equal(5);

 });




 it('should subtract two numbers', () => {

 expect(subtract(5, 3)).to.equal(2);

 });

});

Write Implementation Code:

• • Implement the functions being tested (e.g., calculator.js).

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function add(a, b) {

 return a + b;

}




function subtract(a, b) {

 return a - b;

}




module.exports = { add, subtract };

Run Tests:

• Execute the tests using Mocha.

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npx mocha

Review Test Results:

• Analyze the test results to ensure all tests pass, indicating that the units of code are functioning correctly.

By writing unit tests in Node.js, developers can verify the behavior of individual functions or modules, catch regressions, and build confidence in the correctness of their code.