스프링 빈 조회 질문입니다

스프링 빈 조회할때 검증할때 isInstanceOf로 타입 비교를 할 때 느낌상으로는 MemberService 인터페이스를 넣어야될것같은데 MemberServiceImpl이 들어가는 이유가궁금합니다... 너무 당연하긴하지만 MemberService가 들어가도 검증이 되는지 궁금합니다.

그리고 하나 더 궁금한건 객체 타입이면 memberService이렇게 들어가면되는데 확장자 이름까지 들어가는지궁금합니다. ex) MemberServiceImpl -> MemberServiceImpl.class

package hello.core.beanfind;
import hello.core.AppConfig;
import hello.core.member.MemberService;
import hello.core.member.MemberServiceImpl;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import
org.springframework.context.annotation.AnnotationConfigApplicationContext;
import static org.assertj.core.api.Assertions.*;
class ApplicationContextBasicFindTest {
 AnnotationConfigApplicationContext ac = new
AnnotationConfigApplicationContext(AppConfig.class);
 @Test
 @DisplayName("빈 이름으로 조회")
 void findBeanByName() {
 MemberService memberService = ac.getBean("memberService", 
MemberService.class);
 assertThat(memberService).isInstanceOf(MemberServiceImpl.class);
 }
 @Test
 @DisplayName("이름 없이 타입만으로 조회")
 void findBeanByType() {
 MemberService memberService = ac.getBean(MemberService.class);
 assertThat(memberService).isInstanceOf(MemberServiceImpl.class);
 }
 @Test
 @DisplayName("구체 타입으로 조회")
 void findBeanByName2() {
 MemberServiceImpl memberService = ac.getBean("memberService", 
MemberServiceImpl.class);
 assertThat(memberService).isInstanceOf(MemberServiceImpl.class);
 }
 @Test
 @DisplayName("빈 이름으로 조회X")
 void findBeanByNameX() {
 //ac.getBean("xxxxx", MemberService.class);
 Assertions.assertThrows(NoSuchBeanDefinitionException.class, () ->
ac.getBean("xxxxx", MemberService.class));
 }
}