如何调整测试助手来解释测试用户的模型(元编程)

I've followed Hartl's chapter 8 to develop a log_in_as test helper. Now I wanted to do some metaprogramming by adding type as a parameter. Type specifies which model the user is from. There are two models (Member and Organization) each of which can log in using the same page / create method (through if-else statement). to develop a lo