Spring Boot Isolation.SERIALIZABLE not working - spring

Question

I need help with this scenario, in theory the isolation level of Serializable should stop delete from happening, but in this scenario it still deletes the row with id 1, I have tried #EnableTransactionManagement and isolation repeatable read, it still doesn't block the delete nor cause the delete to throw exception
In summary, I need to stop any delete invocation whenever the update method is still ongoing
I am using H2 in memory database for this sample
Thanks
Entity:
public class Something {
#Id
private Integer id;
private String name;
private String desc;
}
Repo:
public interface SomeRepository extends JpaRepository<Something, Integer> {
}
Service:
#Service
public class SomeService {
#Autowired
private SomeRepository someRepository;
public void deleteSomething2(Something something) {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
someRepository.delete(something);
}
#Transactional(isolation = Isolation.SERIALIZABLE)
public void updateSomething2(Something something) {
Something something1 = someRepository.findById(1).get();
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
e.printStackTrace();
}
something1.setName("namanama");
someRepository.saveAndFlush(something1);
}
Test:
#RunWith(SpringRunner.class)
#SpringBootTest
public class DemoApplicationTests {
#Autowired
private SomeService service;
#Test
public void test() throws Exception {
ExecutorService executorService = Executors.newFixedThreadPool(10);
List<Future> futures = new ArrayList<>();
futures.add(executorService.submit(() -> service.updateSomething2(Something.builder().id(1).name("namaone").build())));
futures.add(executorService.submit(() -> service.deleteSomething2(Something.builder().id(1).build())));
while(futures.stream().filter(f -> f.isDone() == false).count() > 0) {
Thread.sleep(3000);
}
List<Something> all = service.findAll();
System.out.println(all);
}
}