为什么controller.should_receive（：before_filter_name）在rspec中失败？

Question

我们在controller.should_receive(:before_filter_name)中使用rspec通过我们的rails 3.2 rspec中的before过滤器。但对于某些before filter，rspec会返回错误。

以下是过滤器check_availability之前的def：

def check_availability
      if find_config_const('sales_lead', 'customerx').nil? or find_config_const('sales_lead', 'customerx') == 'false'
        redirect_to authentify.signin_path, :notice => "Quit!"
      end
end

在控制器中，前过滤器：

before_filter :require_employee
before_filter :load_customer
before_filter :check_availability

要绕过check_availability，我们将以下代码放在rspec中作为控制器：

before(:each) do
      controller.should_receive(:require_signin) 
      controller.should_receive(:check_availability)          
end

过滤器require_signin没问题。但是对于第二个过滤器，有一个错误：

 2) Customerx::SalesLeadsController GET 'new' should redirect user without proper right
     ←[31mFailure/Error:←[0m ←[31mcontroller.should_receive(:check_availability)←[0m
       ←[31m(#<Customerx::SalesLeadsController:0x6fb3478>).check_availability(any args)←[0m
       ←[31m    expected: 1 time←[0m
       ←[31m    received: 0 times←[0m
←[36m     # ./spec/controllers/customerx/sales_leads_controller_spec.rb:7:in `block (2 levels) in <module:Customerx>'←[0m

我们不太明白should_receive在这里是如何运作的。我们已经看到了一些像这样的情况，并希望找出导致rspec失败的原因。谢谢你的帮助。