springboot中junit回滚的作用是什么

<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>

package com.mos.quote;

import com.mos.quote.model.Area;
import com.mos.quote.service.IAreaService;
import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.Rollback;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class QuoteApplicationTests {

  @Autowired
  private IAreaService areaService;

  @Test
  public void contextLoads() {
  }

  @Test
  public void testUpdate(){
    Area area = new Area();
    area.setCode("001003");
    area.setName("洛阳市");
    Integer result = areaService.update(area);
    Assert.assertEquals(1, (long)result);
  }

  @Test
  @Transactional
  @Rollback
  public void testUpdate4Rollback(){
    Area area = new Area();
    area.setCode("001001");
    area.setName("郑州市123");
    Integer result = areaService.update(area);
    Assert.assertEquals(1, (long)result);
  }

}