Contract tests example

DoctrineUserRepositoryTest.php

<?php

class DoctrineUserRepositoryTest extends UserRepositoryTest
{
    public function setUp()
    {
        // do something to bootstrap doctrine and set up DB fixtures
        $this->userRepository = new DoctrineRepository(/* lots of dependencies */);
    }
    
    public function tearDown()
    {
        // do something to clean up DB
    }
}

InMemoryUserRepository.php

<?php

class InMemoryUserRepository implements UserRepository
{
    private $users = [];
  
    public function create(User $user) : void
    {
        if ($this->findByEmail($user->email())) {
            throw new DuplicateUserException();
        }
      
        $this->users[] = $user;
    }
    
    public function findByEmail(string $email) : ?User
    {
        foreach ($users as $user) {
            if ($user->email() == $email) { 
               return $user; 
            }
        }
    }
}

InMemoryUserRepositoryTest.php

<?php

class InMemoryUserRepositoryTest extends UserRepositoryTest
{
    public function setUp()
    {
        $this->userRepository = new InMemoryUserRepository();
    }
    
    // don't put any tests here
}

UserRepository.php

<?php

interface UserRepository
{
    /** @throws DuplicateUserException */
    public function create(User $user) : void;
    
    public function findByEmail(string $email) : ?User;
}

UserRepositoryTest.php

<?php

/** Contract tests for any well-behaved UserRepository */
abstract class UserRepositoryTest extends TestCase
{
    /** @var UserRepository */
    protected $userRepository;

    function testItStoresAUser()
    {
        $user = new User(/* ... */, '[email protected]');
      
        $this->userRepository->create($user);
        
        $this->assertEquals($this->userRepository->findByEmail('[email protected]');
    }
                            
    function testItReturnsNullWhenNoUser()
    {
        $this->assertNull($this->userRepository->findByEmail('[email protected]'));  
    }
                            
    function testItDoesNotAllowDuplicateEmails()
    {
        $user = new User(/* ... */, '[email protected]');
        $this->userRepository->create($user);
        
        $this->setExpectedException(DuplicateUserException::class);
        
        $user2 = new User(/* ... */, '[email protected]');
        $this->userRepository->create($user2);
    }
}