🧪 Unit Testing Demo with Jest

A practice application designed to help you learn and master unit testing using Jest. This project provides sample functions and clear instructions to get you started with Test-Driven Development (TDD).

📖 Overview

This repository contains a complete learning environment for practicing Jest unit testing. It includes:

• Sample functions to test in dataProcessor.js
• Visual instruction guide in index.html
• Step-by-step setup process
• Best practices and tips

🚀 Quick Start

Follow these steps to set up your Jest testing environment:

1. Initialize Node Environment

npm init -y

This creates a package.json file with default configuration.

2. Install Jest

npm install --save-dev jest

3. Create Tests Directory

mkdir __tests__

Jest automatically looks for test files in the __tests__ directory.

4. Write Unit Tests

Create test files like __tests__/dataProcessor.test.js to test the functions in dataProcessor.js.

5. Configure package.json

Add the test script to your package.json:

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

6. Run Your Tests

npm test

📁 Project Structure

unit-testing-demo/
├── README.md              (this file)
├── index.html             (visual instruction guide)
├── style.css              (styling for instruction page)
├── dataProcessor.js       (functions to test)
├── package.json           (created after npm init)
└── __tests__/             (your test files go here)
    └── dataProcessor.test.js

🎯 Functions to Test

The dataProcessor.js file contains two functions to test:

1. countWords(text)

• Purpose: Counts the number of words in a given text string
• Test scenarios: Normal text, empty strings, strings with extra spaces, null/undefined inputs
• Example: countWords("hello world") returns 2

2. findMax(numbers)

• Purpose: Finds the maximum number in an array of numbers
• Test scenarios: Arrays with positive numbers, negative numbers, mixed arrays, single element arrays
• Example: findMax([1, 5, 3, 9, 2]) returns 9

💡 Testing Best Practices

1. Test Structure

• Use describe() blocks to group related tests
• Write descriptive test names that explain what is being tested
• Follow the AAA pattern: Arrange, Act, Assert

2. Test Coverage

• Happy Path: Test with valid, expected inputs
• Edge Cases: Test with boundary values (empty arrays, zero, etc.)
• Error Cases: Test invalid inputs and error handling
• Null/Undefined: Test with null and undefined values

3. Jest Matchers

Common Jest matchers you'll use:

• toBe() - Exact equality
• toEqual() - Deep equality
• toThrow() - Function throws an error
• toBeTruthy() / toBeFalsy() - Boolean testing
• toBeNull() / toBeUndefined() - Null/undefined testing

4. Test Organization

describe('FunctionName', () => {
    test('should handle normal case', () => {
        // Test implementation
    });

    test('should handle edge case', () => {
        // Test implementation
    });

    test('should throw error for invalid input', () => {
        // Test implementation
    });
});

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Need help? Open index.html in your browser for a visual guide, or refer to the Jest documentation for more advanced features.