OCP·DIP와 생성자 주입의 경계

package board.member;

import java.util.Objects;

public final class CoupledMemberRegistrationService {
    private final MemberRepository members =
            new MemoryMemberRepository();
    private final PasswordHasher passwordHasher =
            new Pbkdf2PasswordHasher(
                    PasswordHashSettings.productionDefaults());

    public Member register(SignUpCommand command) {
        Objects.requireNonNull(command, "command must not be null");
        if (members.existsByEmail(command.email())) {
            throw new DuplicateEmailException(command.email());
        }
        String passwordHash = passwordHasher.hash(
                command.rawPassword());
        return members.save(Member.signUp(
                command.email(), command.name(), passwordHash));
    }
}

package board.member;

import java.util.Objects;

public final class MemberRegistrationService {
    private final MemberRepository members;
    private final PasswordHasher passwordHasher;

    public MemberRegistrationService(
            MemberRepository members,
            PasswordHasher passwordHasher
    ) {
        this.members = Objects.requireNonNull(
                members, "members must not be null");
        this.passwordHasher = Objects.requireNonNull(
                passwordHasher, "passwordHasher must not be null");
    }

    public Member register(SignUpCommand command) {
        Objects.requireNonNull(command, "command must not be null");
        if (members.existsByEmail(command.email())) {
            throw new DuplicateEmailException(command.email());
        }
        String passwordHash = passwordHasher.hash(
                command.rawPassword());
        return members.save(Member.signUp(
                command.email(), command.name(), passwordHash));
    }
}

package board.member;

import java.util.Optional;
import org.junit.jupiter.api.Test;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatNullPointerException;
import static org.assertj.core.api.Assertions.assertThatThrownBy;

final class MemberRegistrationServiceInteractionTest {
    @Test
    void 필수_역할이_null이면_생성_즉시_거절한다() {
        var members = new RecordingMemberRepository(false);
        var hasher = new RecordingPasswordHasher();

        assertThatNullPointerException()
                .isThrownBy(() -> new MemberRegistrationService(
                        null, hasher))
                .withMessage("members must not be null");
        assertThatNullPointerException()
                .isThrownBy(() -> new MemberRegistrationService(
                        members, null))
                .withMessage("passwordHasher must not be null");
    }

    @Test
    void 중복_이메일이면_해시와_저장을_호출하지_않는다() {
        var members = new RecordingMemberRepository(true);
        var hasher = new RecordingPasswordHasher();
        var service = new MemberRegistrationService(members, hasher);

        assertThatThrownBy(() -> service.register(new SignUpCommand(
                "[email protected]", "회원", "secret-1234")))
                .isInstanceOf(DuplicateEmailException.class);

        assertThat(members.existsCalls).isEqualTo(1);
        assertThat(hasher.hashCalls).isZero();
        assertThat(members.saveCalls).isZero();
    }

    private static final class RecordingMemberRepository
            implements MemberRepository {
        private final boolean duplicate;
        private int existsCalls;
        private int saveCalls;

        private RecordingMemberRepository(boolean duplicate) {
            this.duplicate = duplicate;
        }

        @Override
        public boolean existsByEmail(String email) {
            existsCalls++;
            return duplicate;
        }

        @Override
        public Member save(Member member) {
            saveCalls++;
            return member.identifiedBy(saveCalls);
        }

        @Override
        public Optional<Member> findByEmail(String email) {
            return Optional.empty();
        }
    }

    private static final class RecordingPasswordHasher
            implements PasswordHasher {
        private int hashCalls;

        @Override
        public String hash(String rawPassword) {
            hashCalls++;
            return "{recording}";
        }

        @Override
        public boolean matches(
                String rawPassword,
                String encodedPasswordHash
        ) {
            return false;
        }
    }
}