JpaEventBaseEntity test

@Test
    public void JpaEventBaseEntity() throws InterruptedException {
        Member member = new Member("member1");
        memberRepository.save(member); //@Prepersist

        Thread.sleep(100);
        member.setUsername("member2");

        em.flush();
        em.clear();

        Member findMember = memberRepository.findById(member.getId()).get();

        System.out.println("findMember.getCreateDate() = " + findMember.getCreateDate());
        System.out.println("findMember.getUpdateDate() = " + findMember.getUpdateDate());
    }

Thread.sleep을 해준 이유가 무엇인가요??