How to define common setup and teardown logic for all tests in ruby's Test::Unit::TestCase?

Question

Assume there are potentially expensive operations to be performed in setup or teardown that are same for all tests and whose results doesn't get messed with during test runs. It seems not right to me to have them run before/after every single test.

So is there a preferred way to run setup/teardown code only before the first test is executed and only after the last test ran?

Edit: The particular case I'm working on should test some extensions to Net::FTP and thus establishes a FTP connection and sets up some remote objects for testing:

class TestFTPExtensions < Test::Unit::TestCase
  def setup
    # Setup connection
    @ftp = Net::FTP.new 'localhost', 'anonymous'
    @ftp.passive = true

    # Create remote test directory
    @ftp.mkdir 'dir'

    # Create remote test file
    path = File.join Dir.tmpdir, 'file'
    File.open path, 'w' do |f|
      @ftp.put f
    end
    File.delete path
  end

  def teardown
    @ftp.rmdir 'dir'
    @ftp.delete 'file'
    @ftp.close
  end

  # imagine some tests here that don't change/remove any remote objects

end

Solution

Thanks to Andrew I found an answer to this here on stackoverflow.

However in the course of trying to find an answer I also noticed that in the 1.9.x branch the standard testing framework was switched to MiniTest. So actually I'm using that for testing right now. This answer explains how to achieve the same with MiniTest.