日付までの週または月にある日付を見つける方法。
days_for_week should return 19,20,21 (assuming current date is 21st)
days_for_month should return 1..21 (assuming current date is 21st)
日付までの週または月にある日付を見つける方法。
days_for_week should return 19,20,21 (assuming current date is 21st)
days_for_month should return 1..21 (assuming current date is 21st)