Testing unique constraint in @DataJpaTest

I wrote this test to verify unique constraint on Domain.name in the database. But it doesn't work: I expect an exception to be thrown on the domainRepository.saveAndFlush(domainDuplicate) operation, but the test ends successfully.

@RunWith(SpringRunner::class)
@DataJpaTest
class DomainRepositoryTest {

    @Autowired
    private lateinit var util: TestEntityManager
    @Autowired
    private lateinit var domainRepository: DomainRepository

    @Test
    fun testNonUniqueDomainSave() {
        // Arrange
        val domain = Domain(name = "name")
        util.persist(domain)
        util.flush()
        util.clear()

        val domainDuplicate = domain.copy(id = 0L)

        // Act
        domainRepository.saveAndFlush(domainDuplicate)
        // Exception is expected
    }
}

Test log (shortened):

INFO 13522 --- [           main] o.s.t.c.transaction.TransactionContext   : Began transaction (1) for test context [DefaultTestContext@8f8717b testClass = DomainRepositoryTest,...]; transaction manager [org.springframework.orm.jpa.JpaTransactionManager@65f36591]; rollback [true]

Hibernate: insert into domains (name, id) values (?, ?)
Hibernate: insert into domains (name, id) values (?, ?)
Hibernate: insert into domains (name, id) values (?, ?)

INFO 13522 --- [           main] o.s.t.c.transaction.TransactionContext   : Rolled back transaction for test: [DefaultTestContext@8f8717b testClass = DomainRepositoryTest, ...], attributes = map[[empty]]]

Question: How to fix this test? Additional question: Why 3 insert operations in log?

Database: H2