Rails提供的测试routes的helper有3个：

assert_generates(expected_path, options, defaults={}, extras = {}, message=nil)
只返回根据options生成的路由列表里第一条命中的，再与expected_path比较，不适合有多种形态URL的情况

assert_recognizes(expected_options, path, extras={}, message=nil)
用来判断URL是否能达到期待的controller 和action，path可以是Hash，可传入POST或GET等方法。

assert_routing(path, options, defaults={}, extras={}, message=nil)
同时测试assert_generates 和 assert_recognizes，适合唯一映射的情况

还有个更重要的问题是，测试文件要放在哪里？

应该放在 test/integration 目录下。先有个概念：unit 是用来测试 model，functional 用来测试 controller 及其 actions 的，integration 是用来做跨多个 controller 测试。functional 比 integration 要快些，因为它掉过了一些初始化操作，比如roules的初始化。所以只有 integration 才适合做 routes 测试。

# test/integration/routes_test.rb
require "#{File.dirname(__FILE__)}/../test_helper"

class RoutesTest < ActionController::IntegrationTest
    # Rails提供的helper不能直接用来测试subdomains，所以需要自己扩展一个helper
    include RoutesTestHelper

    # test subdomains
    def test_should_have_subdomains_routing
      # test show action
      opts = { :controller => "post", :action => "show", :id => "1" }
      assert_recognizes_uri opts,"http://myapp.com/post/show/1"

      assert_recognizes_uri opts,"http://post.myapp.com/show/1"

      assert_recognizes_uri opts,"http://post.myapp.com/1"

      # test index action
      opts = { :controller => "post", :action => "index" }

      assert_recognizes_uri opts,"http://www.myapp.com/post"
      assert_recognizes_uri opts,"http://myapp.com/post"

      assert_recognizes_uri opts,"http://post.myapp.com/"

      assert_recognizes_uri opts,"http://post.myapp.com/index"
  
    end

end