public void Save_WhenEntityReferencesTransientInstance_WillThrowImmediately() { Customer c = Om.CreateCustomer(); Order o = Om.CreateOrder(); //Order now has a reference to a transient (unsaved) Customer o.Customer = c; var ex = Assert.Throws <PropertyValueException>(() => Nh.CurrentSession.Save(o)); Assert.That(ex.Message, Is.StringContaining("not-null property references a null or transient value")); }