Testing Strategies

A unit test (PHPUnit, from Level 2) verifies one class in isolation; a feature/integration test verifies several real pieces together — in a framework, often a full HTTP request through routing, a controller, and a test database.

class OrderServiceTest extends TestCase
{
    public function testAppliesDiscountForLargeOrders(): void
    {
        $emailSenderMock = $this->createMock(EmailSender::class);
        $service = new OrderService($emailSenderMock);

        $total = $service->calculateTotal(150.0);

        $this->assertEquals(135.0, $total); // 10% off orders over 100
    }
}

createMock() stands in for a real dependency, the same role Mockito/Moq play in Java/C# — letting OrderService's own logic be tested without a real email provider.