Timer.rb

class Timer
  attr_accessor :seconds

  def initialize(value = 0)
    @seconds = value
  end

  def to_s
    time_left = @seconds

    # hours
    hh = (time_left / 3600).floor.to_s.rjust(2, "0")

    # minutes
    time_left = time_left % 3600
    mm = (time_left / 60).floor.to_s.rjust(2, "0")

    # time_left should be remaining seconds
    ss = (time_left % 60).to_s.rjust(2, "0")

    "#{hh}|#{mm}|#{ss}"
  end
end

timer_spec.rb

require 'timer'
require 'rubygems'
require 'rspec'

describe Timer do
  before(:each) do
    @timer = Timer.new
  end

  it "should initialize to 0 seconds" do
    @timer.seconds.should == 0
  end

  it "should display 0 seconds as 00|00|00" do
    @timer.seconds = 0
    @timer.to_s.should == "00|00|00"
  end

  it "should display 12 seconds as 00|00|12" do
    @timer.seconds = 12
    @timer.to_s.should == "00|00|12"
  end

  it "should display 66 seconds as 00|01|06" do
    @timer.seconds = 66
    @timer.to_s.should == "00|01|06"
  end

  it "should display 4000 seconds as 01|06|40" do
    @timer.seconds = 4000
    @timer.to_s.should == "01|06|40"
  end
end