Spring Boot transactional test allows to violate unique constraint on update - jpa

Question

I have a DB (Postgres) table with a unique constraint for one column. I have a test marked with #Transactional annotation, that updates that unique column value to a not unique value. I expect that the update operation should fail, but it executes successfully. Moreover, when I get updated object from the database (inside the same transaction), the column value is updated there.
The simplified version of JPA entity:
#Entity
#Table(name = "entities")
public class Entity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
// The unique column
#Column(name = "name", unique = true)
#NotNull
private String name;
...
}
The simplified version for the test:
#Test
#Transactional
public void test() {
Entity firstEntity = new Entity();
firstEntity.setName("First Entity Name");
// This just calls corresponding JPA repository .save method
entityService.create(firstEntity);
Entity secondEntity = new Entity();
secondEntity.setName("Second Entity Name");
entityService.create(secondEntity);
// Update name to a not unique value
secondEntity.setName(firstEntity.getName);
// This calls corresponding JPA repository .save method.
// It also catches DataIntegrityViolationException and throws
// a more user friendly exception instead
entityService.update(secondEntity);
}
This code works as I expect, if #Transactional annotation is removed or transaction is committed. I also tried to call EntityManager.flush(), as advised here, but this code throws ConstraintViolationException after resulting data is flushed, so I can't test that my entityService.update method works correctly and throws proper exception.
Please also note that if I try to create a new entry with not unique data in transactional test (not update), then test works as expected -
DataIntegrityViolationException is thrown when not unique entity is created.
Could somebody clarify if it is possible to make update scenario work as expected keeping test transactional so I don't need to care about data clean up?