I don't know why Transaction doesn't work in spring boot test

Question

    @Test
    public void 물건_구매_실패_테스트() {
        Store store = this.storeService.saveStore("store", StoreType.KOREAN);
        Item item = this.itemService.itemSave(store.getStoreId(), "비빔밥", 8000, 1);
        Customer c1 = this.customerService.customerSave("c1", 5000);
        Customer c2 = this.customerService.customerSave("c2", 10000);
        Customer c3 = this.customerService.customerSave("c3", 10000);

        {
            IllegalStateException illegalStateException = assertThrows(IllegalStateException.class,
                () -> this.customerService.buyItem(c1.getCustomerId(), item.getItemId())
            );
            assertThat(illegalStateException.getMessage()).isEqualTo("소지금보다 비싼 물건을 구매할 수 없습니다.");
        }

        {
            CustomerItem customerItem = this.customerService.buyItem(c2.getCustomerId(), item.getItemId());
            assertThat(customerItem.getCustomerId()).isEqualTo(c2.getCustomerId());
            assertThat(customerItem.getItemId()).isEqualTo(item.getItemId());
        }

        {
            IllegalStateException illegalStateException2 = assertThrows(IllegalStateException.class,
                () -> this.customerService.buyItem(c3.getCustomerId(), item.getItemId())
            );
            assertThat(illegalStateException2.getMessage()).isEqualTo("남은 재고가 없습니다.");
        }

    }

    @Transactional(rollbackFor = IllegalStateException.class)
    public CustomerItem buyItem(long customerId, long itemId) {
        Item item = this.itemService.minusRemained(itemId);
        Customer customer = this.minusPoint(customerId, item);
        CustomerItem customerItem = this.customerItemService.customerItemSave(customer.getCustomerId(), item.getItemId());
        return customerItem;
    }

    public Item minusRemained(long itemId) {
        Item item = this.itemRepository.findById(itemId)
            .orElseThrow(() -> new IllegalStateException("해당하는 물품이 없습니다."));

        if (item.getRemained() == 0) {
            throw new IllegalStateException("남은 재고가 없습니다.");
        }

        item.setRemained(item.getRemained() - 1);
        return item;
    }

this is my code. And at test, I can pass first test case. But the remain does not rollback. so after first test, item's remained became 0.

I want to buyItem method to rollback if IllegalStateException has come. Thank you.

I tried using new entity. And it worked well. But I am using spring data JPA. So I want to utilize EntityManager.