Я только проектирую систему, поэтому абстрактный пример

class User extends ActiveRecord

class UserManager
{
    public function findByEmail($email)
    {
        return User::find()->where(['email' => $email])->one();
    }
}

class SendPrivateMessage
{
    public $emails = [];
    public $message;

    private $_userManager;
    private $_currentUser;

    public function __construct($userManager, $currentUser)
    {
        $this->_userManager = $userManager;
        $this->_currentUser = $currentUser;
    }

    public function send()
    {
        foreach ($this->emails as $email)
        {
            $user = $this->findByEmail($email);
            if ($user->privateMessageIsDisable()) {
                $user->sendMessage($this->_currentUser, $this->message);
            }
        }
    }

    public function findByEmail($email)
    {
        return $this->_userManager->findByEmail($email);
    }
}

Теперь как я вижу тестирование без базы данных

class UserManagerMock
{
    public function findByEmail($email)
    {
        $data = AbstractBase::get($email); // Нужен этот механизм
        return new UserMock($data);
    }
}