Building Reliable PHP Symfony Apps: The Role of Unit and Functional Testing

• Early bug detection: Unit tests can catch bugs early in the development cycle, making it easier and cheaper to fix them.
• Isolation: Unit tests allow you to test each unit of code in isolation, making it easier to identify and fix issues.
• Refactoring support: Unit tests provide confidence that refactoring or modifying a unit of code does not introduce new bugs.
• Documentation: Unit tests serve as documentation for the expected behavior of individual units of code.
• Faster feedback: Unit tests are generally faster to execute compared to functional tests, providing quick feedback during development.

// CartService.php
class CartService
{
    private $priceCalculator;

    public function __construct(PriceCalculator $priceCalculator)
    {
        $this->priceCalculator = $priceCalculator;
    }

    public function calculateTotalPrice(array $items): float
    {
        $total = 0;

        foreach ($items as $item) {
            $total += $this->priceCalculator->calculatePrice($item);
        }

        return $total;
    }
}

// CartServiceTest.php
use PHPUnit\Framework\TestCase;

class CartServiceTest extends TestCase
{
    public function testCalculateTotalPrice()
    {
        $priceCalculatorMock = $this->createMock(PriceCalculator::class);
        $priceCalculatorMock->method('calculatePrice')
            ->willReturnMap([
                ['item1', 10.0],
                ['item2', 15.0],
            ]);

        $cartService = new CartService($priceCalculatorMock);

        $items = ['item1', 'item2'];

        $totalPrice = $cartService->calculateTotalPrice($items);

        $this->assertEquals(25.0, $totalPrice);
    }
}

• End-to-end coverage: Functional tests verify the system as a whole, ensuring that all components work together correctly.
• Real-world scenarios: Functional tests simulate real user interactions, providing confidence in the system's behavior from a user's perspective.
• Integration testing: Functional tests can uncover integration issues between different parts of the application.
• Regression testing: Functional tests help ensure that existing functionality continues to work as expected when making changes.

// LoginTest.php
use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;

class LoginTest extends WebTestCase
{
    public function testSuccessfulLogin()
    {
        $client = static::createClient();

        $crawler = $client->request('GET', '/login');

        $form = $crawler->selectButton('Login')->form();
        $form['username'] = 'john';
        $form['password'] = 'password';

        $client->submit($form);

        $this->assertResponseRedirects('/dashboard');
    }
}