TDD or not to be

Jakub Nieznalski

Is the code developed using Test-Drived Development better than the one using Test After technique?

TDD Experiments in IBM and Microsoft

 D. S. Janzen

E. M. Laurie Williams

Conclusion 1: It does not matter if the code was written using TDD or Test After

Conclusion 2: The code that was written by developer with more years of experience in programming is better in terms of OO metrics

But is it really like that?

 def workdays_between (ts_from, ts_to)  wdays = (ts_to.to_i - ts_from.to_i) / 360.0 / 240
  if wdays > 1
    tsfd    = ts_from.to_date # midnight
    tstd    = ts_to.to_date
    days    = wdays.truncate
    weeks   = days  / 7
    wdays  -= weeks * 2
    wdays  += 1 if weeks > 0 && ts_to.cwday > 5
    days    = ts_to.cwday - ts_from.cwday
    days   += 7 if days < 0
    if days > 1
      from = tsfd
      (days - 1).times do |i|
        from  += 1.day
        wdays -= 1 if from < tstd && from.cwday > 5 # substract Sat or Sun inbetween
      end
    end
    # ALe 2013-10-19: changed boundaries to EXCLUDE ts_from and ts_to themself (if they SAY thei did it on a holiday, we believe them)
    Holidays.between(ts_from + 1.day, ts_to - 1.day, :de).each do |h| # VERY convenient, isn't it? Thanks, Alex Dunae
      wdays -= 1 unless h[:date].cwday > 5
    end
  end
  wdays < 0 ? 0 : wdays
end

 def weekdays(ts_from, ts_to)
  (ts_from...ts_to).select do |day|
    day.weekday? || day == ts_from || day == ts_to
  end.count
end

def day_part_difference ts_from, ts_to
   day_part(ts_to) - day_part(ts_from)
end

def day_part day
  day - day.midnight
end

def holidays(ts_from, ts_to)
  Holidays.between(ts_from.next_day, ts_to.prev_day,  :de).select{|day| day[:date].weekday? }.count
end

def workdays_between (ts_from, ts_to)
  weekdays(ts_from.to_date, ts_to.to_date) + day_part_difference(ts_from, ts_to) - holidays(ts_from, ts_to)
end

Think about interface

 class Contract
    has_one :verification

 def PercentageCalculator

  def calculate_percentage(contracts)
    contract.select do |c| 
      c.verification.positive == true
    end.count/contract.count
  end
end

Test first

 describe Calculator do
  describe "#calculate_percentage" do
    it "returns percentage of positives";
      Calculator.new(something).calculate_percentage
   end
end

class Calculator    def initialize(collection)
      @collection = collection
    end

  def calculate_percentage
    collection.select{|item| item.positive? }/ collection.size
  end
end

 class Contract
   delegate :positive, :to => :verification
 ...
Calculator.new(contracts).calculate_percentage

What do you think?