dip package

user_data.go

package data

import (
	"database/sql"
	"golang-test-sample/dip/service"
)

type UserRepositoryImpl struct {
	DB *sql.DB
}

func (res *UserRepositoryImpl) Get(id int) (*service.User, error) {
	user := &service.User{}

	if err := res.DB.QueryRow("SELECT * FROM user WHERE id = ? LIMIT 1", id).Scan(
		&user.ID,
		&user.Name,
		&user.Age,
	); err != nil {
		return nil, err
	}

	return user, nil
}

func (res *UserRepositoryImpl) Put(user *service.User) error {
	_, err := res.DB.Exec("INSERT INTO user (name, age) VALUES (?, ?) ",
		user.Name, user.Age)
	if err != nil {
		return err
	}

	return nil
}

user_service.go

package service

// Good: service（内側） から data（外側） への依存（参照）が存在しない。

type User struct {
	ID   int
	Name string
	Age  int
}

type UserRepository interface {
	Get(id int) (*User, error)
	Put(user *User) error
}

func ResisterUser(user *User, res UserRepository) error {
	err := res.Put(user)
	return err
}

func FetchUser(id int, res UserRepository) (*User, error) {
	user, err := res.Get(id)
	if err != nil {
		return nil, err
	}
	return user, nil
}

user_service_test.go

package service

// Good: 外側への依存が存在しない。(errorは例外)
import (
	"errors"
	"testing"
)

type UserRepositoryMock struct {
	Users []*User
}

func (rep *UserRepositoryMock) Get(id int) (*User, error) {
	if id < len(rep.Users) {
		return nil, errors.New("error.")
	}
	return rep.Users[id-1], nil
}

func (rep *UserRepositoryMock) Put(user *User) error {
	rep.Users = append(rep.Users, user)
	return nil
}

func TestUser(t *testing.T) {
	rep := UserRepositoryMock{
		[]*User{},
	}

	user1 := &User{
		1,
		"Alice",
		20,
	}

	err := ResisterUser(user1, &rep)

	if err != nil {
		t.Error("error.")
		return
	}

	user2, err := FetchUser(1, &rep)
	if user2.ID != 1 || user2.Name != "Alice" || user2.Age != 20 || err != nil {
		t.Error("error.")
		return
	}
}