def start_of_quarter(year, quarter)
      case quarter
      when QUARTER_1
        start_of_month(year, 1)
      when QUARTER_2
        start_of_month(year, 4)
      when QUARTER_3
        start_of_month(year, 7)
      when QUARTER_4
        start_of_month(year, 10)
      else
        raise "invalid quarter"
      end
    end
def start_of_quarter(year, quarter)
      case quarter
      when QUARTER_1
        start_of_month(year, 1)
      when QUARTER_2
        start_of_month(year, 4)
      when QUARTER_3
        start_of_month(year, 7)
      when QUARTER_4
        start_of_month(year, 10)
      else
        raise "invalid quarter"
      end
    end
Return the starting date for a particular quarter

 @param year [Integer] the retail year
 @param quarter [Integer] the quarter of the year, a number from 1 - 4
 @return [Date] the start date of the quarter