질문있습니다

package hello.core.beanfind;

import hello.core.discount.DiscountPolicy;
import hello.core.discount.FixDiscountPolicy;
import hello.core.discount.RateDiscountPolicy;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.NoUniqueBeanDefinitionException;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.Map;

import static org.assertj.core.api.Assertions.assertThat;
import static org.junit.jupiter.api.Assertions.assertThrows;

public class ApplicationContextExtendsFindTest {
    AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(TestConfig.class);
    @Test
    @DisplayName("부모 타입으로 조회 시, 자식이 둘 이상 있으면, 중복 오류가 발생한다.")
    void findBeanByParentTypeDuplicate(){

        assertThrows(NoUniqueBeanDefinitionException.class,()->ac.getBean(DiscountPolicy.class));
    }
    @Test
    @DisplayName("부모 타입으로 조회 시, 자식이 둘 이상 있으면, 빈 이름 지정하면 된다.")
    void findBeanByParentTypeBeanName(){
        DiscountPolicy rateDiscountPolicy=ac.getBean("rateDiscountPolicy",DiscountPolicy.class);
        assertThat(rateDiscountPolicy).isInstanceOf(RateDiscountPolicy.class);
    }
    @Test
    @DisplayName("특정 하위 타입으로 조회")
    void findBeanBySubType(){
        RateDiscountPolicy bean=ac.getBean(RateDiscountPolicy.class);
        assertThat(bean).isInstanceOf(RateDiscountPolicy.class);
    }
    @Test
    @DisplayName("부모 타입으로 모두 조회하기")
    void findAllBeanByParentType(){
       Map<String,DiscountPolicy> beansOfType=ac.getBeansOfType(DiscountPolicy.class);
       assertThat(beansOfType).isEqualTo(2);
        for (String key : beansOfType.keySet()) {
            System.out.println("key= "+key+"value="+beansOfType.get(key));
        }
    }
    @Test
    @DisplayName("부모 타입으로 모두 조회하기-Object")
    void findAllBeanByObjectType(){
        Map<String,Object> beansOfType=ac.getBeansOfType(Object.class);
        for(String key:beansOfType.keySet()){
            System.out.println("key = "+key +"value="+beansOfType.get(key));
        }
    }

    @Configuration
    static class TestConfig{
        @Bean
        public DiscountPolicy rateDiscountPolicy(){
            return new RateDiscountPolicy();
        }
        @Bean
        public DiscountPolicy fixDiscountPolicy(){
            return new FixDiscountPolicy();
        }
    }
}

여기서assertThrows(NoUniqueBeanDefinitionException.class,()->ac.getBean(DiscountPolicy.class)); 이 부분이 왜 부모 타입으로 조회하는 건지 이해가 안갑니다. 상속을 한 적도 없고 그냥 타입을 넣어줬을 뿐인데 말이죠..ㅠ