Unit Testing in JavaScript: A Practical Guide with Jest

Think of Unit Testing as a software development technique where you break your software up into small, isolated units and write automated tests that ensure each unit works as expected. In simpler terms, unit testing is about verifying that the smallest pieces of your application — usually functions — behave correctly under different conditions. A unit can be: A function A method A component A utility A hook A service The key idea is isolation. You test one unit at a time, without depending on other parts of the system. For example, instead of testing an entire application flow, you test a single function like: function calculateTotal(price, quantity) { return price * quantity; } Why Unit Testing is Required? Unit testing is not just a best practice — it is a core part of professional software development, especially as applications grow in size and complexity. Without tests, every change introduces risk. With tests, you gain confidence. Here are the real reasons why unit testing is req