Test Doubles and Integration Tests

PHPUnit's createStub() returns canned values and createMock() also verifies calls; libraries like Mockery and Prophecy are alternatives. Prefer fakes (in-memory repositories) over mocking everything. For database code, write integration tests against the real engine (Docker/Testcontainers or a CI service) and wrap each test in a transaction that rolls back. Use framework test clients (Symfony WebTestCase, Laravel HTTP tests) for request-level tests.

<?php
final class RegisterUserTest extends TestCase
{
    public function test_it_dispatches_user_registered(): void
    {
        $users = new InMemoryUserRepository();                    // fake
        $hasher = $this->createStub(PasswordHasher::class);       // stub
        $hasher->method('hash')->willReturn('hashed');
        $events = $this->createMock(EventDispatcherInterface::class);   // mock
        $events->expects($this->once())->method('dispatch')->with($this->isInstanceOf(UserRegistered::class));

        (new RegisterUser($users, $hasher, $events))('[email protected]', 'secret-password');

        $this->assertNotNull($users->findByEmail('[email protected]'));
    }
}

abstract class DatabaseTestCase extends TestCase
{
    protected PDO $pdo;
    protected function setUp(): void { $this->pdo = createPdo(); $this->pdo->beginTransaction(); }
    protected function tearDown(): void { $this->pdo->rollBack(); }
}

Common pitfalls

• Mocking types you don't own (e.g., PDO) instead of wrapping them.
• Testing PostgreSQL code against SQLite.
• Over-specified mocks that break on harmless refactors.

Key points

• Stubs return data; mocks verify calls
• Fakes for repositories
• Real database for integration tests

Further reading: PHPUnit: test doubles