답변에는 Member 엔티티에 관련된 부분도 작성해주셔야 된다고 하셨는데 앞서 다른 테스트 코드는 Member 엔티티에 관련된 부분을 작성하지 않아도 통과가 되었습니다.
우선 Question, Answer, 테스트코드 순서로 차례대로 코드를 달겠습니다.

Question 엔티티

@Entity
@Getter @Setter
public class Question {

    @Id @GeneratedValue
    @Column(name = "question_id")
    private Long id;

    @Column(unique = true, length = 200)
    private String subject;

    @Column(unique = true, columnDefinition = "TEXT")
    private String content;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "member_id")
    private Member member;

    @OneToMany(mappedBy = "question", cascade = CascadeType.REMOVE)
    private List<Answer> answerList;

    private LocalDateTime createDate;
}

Answer 엔티티

@Entity
@Getter @Setter
public class Answer {

    @Id @GeneratedValue
    @Column(name = "answer_id")
    private Long id;

    @Column(columnDefinition = "TEXT")
    private String content;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "member_id")
    private Member member;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "question_id")
    private Question question;

    private LocalDateTime createDate;
}

테스트 코드 - 답변조회 메서드는 실행이 잘됩니다, 질문조회 메서드만 오류가 나는 상태입니다.

@SpringBootTest
@Transactional
class AnswerRepositoryTest {

    @Autowired
    private QuestionRepository questionRepository;

    @Autowired
    private AnswerRepository answerRepository;

    @Test
    public void 답변조회() throws Exception{
        //given
        Question q = new Question();
        q.setSubject("제목입니다.");
        q.setContent("본문입니다.");
        Question savedQuestion = questionRepository.save(q);

        Answer a = new Answer();
        a.setContent("답변입니다.");
        a.setCreateDate(LocalDateTime.now());
        a.setQuestion(questionRepository.findById(savedQuestion.getId()).get());
        Answer savedAnswer = answerRepository.save(a);
        //when
        Answer findByIdAnswer = answerRepository.findById(savedAnswer.getId()).get();

        //then
        assertEquals(findByIdAnswer.getQuestion(),savedQuestion);

    }

    @Test
    public void 질문조회() throws Exception{
        //given
        Question q = new Question();
        q.setSubject("제목입니다.");
        q.setContent("본문입니다.");
        Question saveQuestion = questionRepository.save(q);
        Question question = questionRepository.findById(saveQuestion.getId()).get();


        Answer a = new Answer();
        a.setContent("답변입니다.");
        a.setQuestion(question);
        a.setCreateDate(LocalDateTime.now());
        answerRepository.save(a);

        //when
        List<Answer> answerList = question.getAnswerList();

        //then
        assertEquals(1,answerList.size());
        assertEquals("답변입니다.",answerList.get(0).getContent());

    }
}

여기 오류 코드입니다.