Introduction

In this tutorial, we will be introducing you to the world of Unit Testing, specifically in the context of Dynamic Testing. The goal is to provide a clear understanding of the basic concepts and practical application of Unit Testing.

By the end of this tutorial, you will:
- Understand the basic concepts of Unit Testing and Dynamic Testing.
- Learn to write, execute, and interpret unit tests.
- Be able to apply these testing methods to your own code.

Prerequisites:
- Basic knowledge of HTML and JavaScript.
- Familiarity with a JavaScript testing framework like Jest or Mocha.

Step-by-Step Guide

Concepts of Unit Testing

Unit Testing, as the name suggests, is a method of testing individual units of source code to determine if each one is operating correctly. A 'unit' is the smallest testable part of an application, typically a method in an object or a function in a module.

Dynamic Testing

Dynamic Testing involves testing the software by executing it. In the context of unit testing, dynamic testing would mean executing the individual units of code and checking if they produce the expected results.

Writing Unit Tests

Unit tests are usually written using a unit testing framework. For JavaScript, popular choices include Jest and Mocha. These frameworks provide easy-to-use APIs to define test cases, test suites, and assertions.

Best Practices

• Each unit test should be independent and able to run in isolation.
• Test only one code unit at a time.
• Use clear, descriptive names for your tests.
• Make sure your tests are repeatable and run your test suite before and after each refactor.

Code Examples

Let's suppose we have a function add that adds two numbers:

function add(a, b) {
    return a + b;
}

Here's how we can write a unit test for this function using Jest:

const add = require('./add'); // Assuming add function is in add.js

test('adds 1 + 2 to equal 3', () => {
    expect(add(1, 2)).toBe(3); // expect is used to check if the function produces the expected output
});

In this case, if the add function does not return 3 when passed 1 and 2, the test will fail.

Summary

In this tutorial, we covered the basics of Unit Testing in the context of Dynamic Testing. We learned the concepts behind these testing methods and how to apply them in practical situations.

Next, you can try testing more complex functions or even incorporating mocking in your tests.

Practice Exercises

1. Write a function that takes a string and returns the reversed string. Then write a unit test for this function.

2. Write a function that takes an array of numbers and returns the largest number. Write a unit test for this function.

3. Write a function that takes two numbers and multiplies them. Then write a unit test for this function.

Solutions

// Function
function reverseString(str) {
    return str.split('').reverse().join('');
}

// Test
test('reverseString reverses string', () => {
    expect(reverseString('abcd')).toBe('dcba'); 
});

// Function
function getMax(arr) {
    return Math.max(...arr);
}

// Test
test('getMax returns maximum number in array', () => {
    expect(getMax([1, 2, 3])).toBe(3); 
});

// Function
function multiply(a, b) {
    return a * b;
}

// Test
test('multiply multiplies numbers', () => {
    expect(multiply(2, 3)).toBe(6); 
});

Remember, practice is key when it comes to programming. Keep writing more tests for different types of functions.