Why and What to Test

Why and What to Test

In this lesson — part of Testing Fundamentals — you'll learn why and what to test in PHP and why it matters in real work.

Why it matters

Tests prove your code works and keep it working as you change it.

Key ideas

• What to test
• Arrange-Act-Assert
• Running a test suite
• Good vs. brittle tests

In practice

Here's how it looks in idiomatic PHP:

<?php
use PHPUnit\Framework\TestCase;

final class MathTest extends TestCase {
    public function testAddsNumbers(): void {
        $this->assertSame(5, add(2, 3));
    }
}
// run with: ./vendor/bin/phpunit

PHP note: PHPUnit is the de facto standard: test classes extend TestCase, methods are prefixed test (or use #[Test]), and assertSame checks value plus type.

Try it yourself

Exercise: In PHP, write three tests for a function that reverses a string.

Recap

You now understand why and what to test and can apply it in PHP. Mark this lesson complete and continue to the next one.