class Rack::Test::CookieJar

def for(uri)

use for the given URI.
Return a raw cookie string for the cookie header to 
def for(uri)
  buf = String.new
  delimiter = nil
  each_cookie_for(uri) do |cookie|
    if delimiter
      buf << delimiter
    else
      delimiter = DELIMITER
    end
    buf << cookie.raw
  end
  buf
end