repo.go

type repo struct {
	execSQL  func(query string, args ...interface{}) (sql.Result, error)
	queryRow func(query string, args ...interface{}) func(dest ...interface{}) error
}

func NewRepo(db *sql.DB) repo {
  return repo{
		execSQL: db.Exec,
		queryRow: func(query string, args ...interface{}) func(...interface{}) error {
			return db.QueryRow(query, args...).Scan
		},
	}
}

func (r repo) Add(id, name string) error {
  _, err := r.execSQL(`INSERT INTO tbl (id, name) VALUES ($1, $2)`, id, name)
  
  return err
}

func (r repo) Read(id string) (string, error) {
	var name string
	err := r.queryRow(`SELECT name FROM tbl WHERE id = $1`, id)(&name)
	
	return name, err
}

repo_test.go

func (s *RepoTestSuite) SetupTest() {
	s.subject = NewRepo(s.db)
}

func (s *RepoTestSuite) Test_Add_UnexpectedError() {
	expected := errors.New("bampf")
	s.subject.execSQL = func(string, ...interface{}) (sql.Result, error) { return nil, expected }

	err := s.subject.Add(s.id, s.name)

	s.Equal(expected, err)
}

func (s *RepoTestSuite) Test_Read_UnexpectedError() {
	expected := errors.New("boom")
	s.subject.queryRow = func(string, ...interface{}) func(...interface{}) error {
		return func(...interface{}) error { return expected }
	}

	_, err := s.subject.Read(s.id)

	s.Equal(expected, err)
}