Added following failing spec FIRST

    context "#weekday_name_tomorrow" do
        it "returns tomorrow's week-day name" do
            calendar = Calendar.new
            expect(calendar.weekday_name_tomorrow).to eql( (Time.now + Calendar::SECONDS_IN_ONE_DAY).strftime('%A') )
        end
    end

Then added the simplest implementation in Calendar class to pass the failing specs.