duration.rb

class Duration
  attr_accessor :duration

  def initialize(string)
    @duration = string
  end

  def to_i
    value_units.map(&:to_i).reduce(&:+)
  end

  private

  def value_units
    duration.gsub(' ', '').scan(/(\d+)([a-zA-Z]+)/).map { |value, unit|
      ValueUnit.new(value, unit)
    }
  end
end

class ValueUnit
  attr_accessor :value, :unit

  def initialize(value, unit)
    @value = value
    @unit = unit
  end

  def to_i
    value.to_i * unit_value
  end

  private

  def unit_value
    case unit
    when /^h/ then 3600
    when /^m/ then 60
    when /^s/ then 1
    else 0
    end
  end
end

duration_spec.rb

require 'duration'
require 'spec_helper'

describe Duration do
  context 'seconds' do
    it { Duration.new('1s').to_i.should == 1 }
    it { Duration.new('1sec').to_i.should == 1 }
    it { Duration.new('1 sec').to_i.should == 1 }
  end

  context 'minutes' do
    it { Duration.new('1m').to_i.should == 60 }
    it { Duration.new('1min').to_i.should == 60 }
    it { Duration.new('1 min').to_i.should == 60 }
  end

  context 'hours' do
    it { Duration.new('1h').to_i.should == 3600 }
    it { Duration.new('1hour').to_i.should == 3600 }
    it { Duration.new('1 hour').to_i.should == 3600 }
  end

  context 'mix' do
    it { Duration.new('1h 6 min 40 sec').to_i.should == 4000 }
  end

  context 'unknown unit' do
    it { Duration.new('1 day 1 second').to_i.should == 1 }
  end
end

old_broken_code.rb

def some_method(duration)
  parsed_duration = 0

  if duration.include? 'h'
    parsed_duration += duration.match(/(\d+)h/).captures.first.to_i.send(:hour).to_i
    duration = duration.match(/\d+h(.+)/).captures.first.strip
  end

  parsed_duration += duration.to_i.send(duration.split[1].gsub('min', 'minute').gsub('sec', 'second')).to_i
  parsed_duration
end

Refactors old_broken_code.rb to a class Duration. Added spec, to have an idea what Duration should do; note that not all specs were green with old_broken_code.rb