Rubyで標準出力をナニしたい時に書いたコード ref: http://qiita.com/items/2951

file0.rb

class Display
  attr_accessor :print

 def initialize
    @print = []
  end

  def write(msg)
    @print.push(msg)
  end
end

def display_capture
  disp = Display.new
  $stdout = disp
  yield
  $stdout = STDOUT
  return disp.print
end
def test_hoge
  res = display_capture do
    print 1
    print 2
  end
  assert_equal([1, 2], res)
end