is making a setter method for only test fine?

I'm doing unit test using Mockito and Junit5.

I'm bringing prior study records based on user createdAt field and today date.
So I want to check if my code bring study records but the thing is createdAt is seted up by JPAAuditing.

@Getter
@ToString(callSuper = true)
@Entity
@EntityListeners(AuditingEntityListener.class)
public class User {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
@Column(unique = true, nullable = false)
private String username;
@Column(unique = true, nullable = false)
private String email;
@Column(nullable = false)
private String password;
@Enumerated(EnumType.STRING)
private UserRole role;
@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
@DateTimeFormat(iso = DateTimeFormat.ISO.DATE_TIME)
@CreatedDate
@Column(updatable = false)
private LocalDateTime createdAt;
protected User() {}
protected User(String username, String email, String password) {
this.username = username;
this.email = email;
this.password = password;
this.role = UserRole.USER;
}
public static User of(String username, String email, String password, boolean verified) {
return new User(username, email, password, verified);
}
public void setIdForTest(Long id) {
this.id = id;
}
public void setPasswordForTest(String pw) {
this.password = pw;
}
public void setCreatedAtForTest() {
this.createdAt = LocalDateTime.now();
}
public void setCreatedAtForTest(LocalDateTime localDateTime) {
this.createdAt = localDateTime;
}

}

This is the code that bringing study records

@Override
public UserDTO.UserDetailWithStudyRecords findPriorStudyRecords(User user) {
LocalDateTime joinDate = user.getCreatedAt();
LocalDateTime date = LocalDateTime.now();
List<String> studiedDates = wordQuerydslRepository.findByUserAndCreatedAtBetweenAndGroupBy(
user,
LocalDateTime.of(joinDate.getYear(), joinDate.getMonth(), 1, 0, 0, 0),
LocalDateTime.of(date.getYear(), date.getMonth(), date.toLocalDate().lengthOfMonth(), 23, 59, 59)
);
...
}

I need to manipulate the joinDate. But im curious if making a test method like "setCreatedAtForTest".

[Test Code]

@DisplayName("공부한 날짜 기록을 가져온다.")
@Test
void getStudyRecords() {
User user = UserFixture.getVerifiedUser();
user.setCreatedAtForTest(LocalDateTime.of(2023, 01, 01, 00, 00));
LocalDateTime now = LocalDateTime.now();
List<String> dates = List.of("01/01/2023", "01/02/2023", "02/02/2023", "03/01/2023", "04/01/2023");
given(wordQuerydslRepository.findByUserAndCreatedAtBetweenAndGroupBy(
user,
user.getCreatedAt(),
LocalDateTime.of(now.getYear(), now.getMonth(), now.toLocalDate().lengthOfMonth(), 23, 59, 59))
).willReturn(dates);
}

You have a couple of options for solving this. Firstly, as an alternative, @Carols's suggestion in the comments is correct: you can use add a data.sql file in your test/resources directory that initializes the database with some test entries.

If you wouldn't have this alternative, I would say it's ok to create a package-protected setter for tests. Or even better, a packaged-protected constructor that receives the created date.

protected User(String username, String email, String password) {
this(username, email, password);
}
User(String username, String email, String password, LocalDateTime createdDate) {
this.username = username;
this.email = email;
this.password = password;
this.role = UserRole.USER;
this.createdDate = createdDate;
}

This will allow you to create a user injecting that date from the test fixture or from some test builder that is defined in the same package as the User. Even Uncle Bob has an article here he states that "testing trumps encapsulation" - but, of course, this a measure of last resort: https://blog.cleancoder.com/uncle-bob/2015/07/01/TheLittleSingleton.html