Unit Testing with Jest
Learn unit testing with Jest for Node.js applications. This is a foundational concept in server-side JavaScript development that professional developers rely on daily. The explanations below are written to be beginner-friendly while covering the depth and nuance that comes from real-world Node.js experience. Take your time with each section and practice the examples
45 min•By Priygop Team•Last updated: Feb 2026
Jest Testing Framework
Jest is a popular JavaScript testing framework that provides a complete testing solution for Node.js applications. It includes test runners, assertion libraries, mocking capabilities, and code coverage.
Jest Setup and Configuration
Example
// Install Jest
npm install --save-dev jest
// package.json
{
"scripts": {
"test": "jest",
"test:watch": "jest --watch",
"test:coverage": "jest --coverage"
},
"jest": {
"testEnvironment": "node",
"collectCoverageFrom": [
"src/**/*.js",
"!src/**/*.test.js"
],
"coverageThreshold": {
"global": {
"branches": 80,
"functions": 80,
"lines": 80,
"statements": 80
}
}
}
}
// Basic test example
// src/utils/calculator.test.js
const { add, subtract, multiply, divide } = require('./calculator');
describe('Calculator', () => {
test('should add two numbers correctly', () => {
expect(add(2, 3)).toBe(5);
expect(add(-1, 1)).toBe(0);
});
test('should subtract two numbers correctly', () => {
expect(subtract(5, 3)).toBe(2);
expect(subtract(0, 5)).toBe(-5);
});
test('should handle division by zero', () => {
expect(() => divide(5, 0)).toThrow('Division by zero');
});
});