Unit test grails with domain objects using GORM functions

I have the following piece of code inside a service class named OrderService in Groovy on Grails. I want to make a unit test for this class. User and Order are domain classed. A user has many orders.

boolean testfun(long userId, lond orderId){

        User user = User.findByUserId(userId)
        if(user == null)return false
        Order order = Order.findByUserAndId(user, orderId)
        if(order == null)return false

        return true
    }

The unit test that I am trying to write is the following (using Spock):

@TestFor(OrderService)
@Mock([User, Order])
class OrderServiceSpec extends Specification{
 def "test funtest"() {

        User user = new User(2)
        Order order = new Order()
        order.metaClass.id = 3// I want to assign the id of the order in domain  
        order.save()        
        user.addToOrders(order)
        user.save()

        expect:
        service.testfun(2,3) == true
}
}

However this test fails because the order is null. Can anyone help me? Another question is: is this test a unit test? or should I write an integration test in grails?