Added empty instance method "date_today" to class Calendar.
With that method in place calendar_spec.rb fails with error

  1) Calendar#date_today returns today's date
     Failure/Error: expect(calendar.date_today).to eql(Time.now.day)

       expected: 28
            got: nil

       (compared using eql?)
     # ./spec/calendar_spec.rb:7:in `block (3 levels) in <top (required)>'