public boolean isPercentageCoupon() {
        return this.policy.isDiscountPercentage();
    }
@Test
    void 할인율_쿠폰이면_true를_반환한다() {
        // given
        Coupon coupon = 쿠픈_생성_독자_사용_할인율_10_퍼센트();

        // when
        boolean result = coupon.isPercentageCoupon();

        // then
        assertThat(result).isTrue();
    }