public interface MemberRepository extends JpaRepository<Member, Long> {
	List<Member> findByUsername(String username);
}

테스트

@SpringBootTest
@Transactional
class MemberRepositoryTest {

	@Autowired
	MemberRepository memberRepository;

	@Test
	public void basicTest() {
		Member member = new Member("member1", 10);
		memberRepository.save(member);

		Member findMember = memberRepository.findById(member.getId()).get();
		assertThat(findMember).isEqualTo(member);

		List<Member> members1 = memberRepository.findAll();
		assertThat(members1).containsExactly(member);

		List<Member> members2 = memberRepository.findByUsername("member1");
		assertThat(members2).containsExactly(member);
	}
}