spec_helper.rb

require "#{File.dirname(__FILE__)}/../lib/transactions.rb"
include Transactions

def capture_stdout(&block)
  original_stdout = $stdout
  $stdout = fake = StringIO.new
  begin
    yield
  ensure
    $stdout = original_stdout
  end
  fake.string
end

class TransactionInput
  def initialize output
    @output = output
  end

  def should_output output
    @output.split("\n").should == output.split("\n")[1..-2].collect{|line| line.strip}
  end
end

def transaction_input input
  TransactionInput.new capture_stdout{ input.split("\n")[1..-2].each{|line| Message.new(line).process} }
end

transaction_spec.rb

require 'spec_helper'

describe "Transaction" do
  it "should handle dummy numerals" do
    transaction_input(%{
        x1    is I
        x5    is V
        x10   is X
        x50   is L
        x100  is C
        x500  is D
        x1000 is M
        how much is x1000 x100 ?
        how much is x1 x1 ?
        how much is x1 x5 ?
      }
      ).should_output(%{
        x1000 x100 is 1100
        x1 x1 is 2
        x1 x5 is 4
      })
  end
end