Why Unit testing in Testing Fundamentals? - Purpose & Use Cases

The Big Idea

What if your code could check itself every time you change it?

The Scenario

Imagine you just wrote a small piece of code to calculate discounts for a shopping app. Every time you change something, you open the app and try different prices manually to see if the discount works correctly.

The Problem

This manual checking is slow and tiring. You might forget some price cases or make mistakes while testing. If the code changes often, you waste a lot of time repeating the same checks, and bugs can sneak in unnoticed.

The Solution

Unit testing lets you write small automatic checks for each part of your code. These tests run quickly and tell you immediately if something breaks, so you don't have to test everything by hand every time.

Before vs After

✗ Before

Run app, enter price 100, check discount manually
Run app, enter price 200, check discount manually

✓ After

assert calculate_discount(100) == 10
assert calculate_discount(200) == 20

What It Enables

Unit testing makes your code safer and saves time by catching errors early with automatic checks.

Real Life Example

A developer changes a function to add a new feature. Thanks to unit tests, they quickly see if the old discount calculations still work without opening the app and clicking around.

Key Takeaways

Manual testing is slow and error-prone.

Unit tests automate checks for small code parts.

They help catch bugs early and speed up development.