$container = new Nette\DI\Container;
$container->addService('authorizator', mock('Nette\Security\IAuthorizator'));
$container->addService('authenticator', mock('Nette\Security\IAuthenticator'));
$container->classes = array(
    'Nette\Security\IAuthorizator' => 'authorizator',
    'Nette\Security\IAuthenticator' => 'authenticator'
);

$container->authenticator
    ->shouldReceive('authenticate')
    ->with('user', 'pass');

// https://github.com/Kdyby/Framework/blob/master/libs/Kdyby/Security/SimpleUserStorage.php
$user = new Nette\Security\User(new Kdyby\Security\SimpleUserStorage, $container);
$user->login('user', 'pass');