PHPUnit Assertions

Assertions express the observable outcome a test expects. The best assertion is usually the narrowest one that communicates a useful failure message.

Prefer Precise Comparisons

assertSame() checks value and type, which is often safer than loose equality. PHPUnit also includes assertions for counts, arrays, strings, files, exceptions, objects, and many other conditions.

Make Failures Explain The Problem

One clear assertion can be better than several broad assertions. When a test needs several values, use assertions that identify the broken part of the response or domain result.

<?php

declare(strict_types=1);

use PHPUnit\Framework\TestCase;

final class ProductResultTest extends TestCase
{
    public function testPublishedProductContainsExpectedFields(): void
    {
        $product = ['id' => 42, 'name' => 'Desk lamp', 'published' => true];

        $this->assertSame(42, $product['id']);
        $this->assertSame('Desk lamp', $product['name']);
        $this->assertTrue($product['published']);
        $this->assertArrayNotHasKey('deleted_at', $product);
    }
}

Common Mistakes

• Using loose comparisons when type matters.
• Asserting only that a response is not null.
• Writing many assertions against unrelated behaviours in one test.
• Forgetting a message or precise assertion when diagnosis would otherwise be difficult.

What To Practise

• Choose precise assertions.
• Use strict comparisons for typed values.
• Keep assertions tied to one behaviour.