에러관련 질문드려요~

안녕하세요. 강사님. 이번 강의에서 

XmlAppContext.java는

package hello.beanfind;

import hello.core.member.MemberRepository;
import hello.core.member.MemberService;
import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.GenericApplicationContext;
import org.springframework.context.support.GenericXmlApplicationContext;
import org.springframework.test.context.web.GenericXmlWebContextLoader;

public class XmlAppContext {

    @Test
    @DisplayName("xml config 테스트해보기")
    void xmlAppContext(){
        ApplicationContext ac = new GenericXmlApplicationContext("appConfig.xml");
        MemberService ms = ac.getBean("memberService", MemberService.class);
        Assertions.assertThat(ac).isInstanceOf(MemberService.class);
    }

}

appConfig.xml은 

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="memberService" class="hello.core.member.MemberServiceImpl" >
        <constructor-arg name="memberRepository" ref="memberRepository" />
    </bean>
    <bean id="memberRepository" class="hello.core.member.MemoryMemberRepository" />


    <bean id="orderService" class="hello.core.order.OrderServiceImpl">
        <constructor-arg name="memberRepository" ref="memberRepository" />
        <constructor-arg name="discountPolicy" ref = "discountPolicy" />
    </bean>
    <bean id="discountPolicy" class="hello.core.discount.RateDiscountPolicy"/>


</beans>

이렇게 작성하였는데 아래와 같은 에러가 나는데요. 

18:22:00.364 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'memberService'

18:22:00.397 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'memberRepository'

18:22:00.420 [main] WARN org.springframework.context.support.GenericXmlApplicationContext - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'memberService' defined in class path resource [appConfig.xml]: Unsatisfied dependency expressed through constructor parameter 0: Ambiguous argument values for parameter of type [hello.core.member.MemberRepository] - did you specify the correct bean references as arguments?

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'memberService' defined in class path resource [appConfig.xml]: Unsatisfied dependency expressed through constructor parameter 0: Ambiguous argument values for parameter of type [hello.core.member.MemberRepository] - did you specify the correct bean references as arguments?

구글링을 해도 원인을 모르겠어서요..ㅜ.ㅜ