rspec-rails和使用let导致变量冲突？

正在编写一些测试并遇到使用let来定义一些变量的问题。

我花了一些时间制作一个最小的失败例子：

 require "spec_helper" describe "Some behavior" do let(:attachments_dir) { "some_test_dir" } before :all do attachments_dir # Commenting out this line makes the tests pass end context "nested 1" do let(:api_params) do { message: { to: "recipient1", from: "sender1"} } end before do puts "nested 1 before " + api_params.to_s end it "nested 1 example 1" do api_params[:message][:to].should == "recipient1" end end context "nested 2" do let(:api_params) do { message: { from: "sender2"} } end before do puts "nested 2 before " + api_params.to_s end it "nested 2 example 1" do api_params[:message][:to].should be_nil end end end 

此测试失败

 nested 1 before {:message=>{:to=>"recipient1", :from=>"sender1"}} nested 2 before {:message=>{:to=>"recipient1", :from=>"sender1"}} expected: nil got: "recipient1" 

但是，注释掉该示例的第8行会导致测试通过

 #attachments_dir 

为什么顶级let干扰嵌套上下文let ？ 这对我来说就像一个RSpec错误，但我想在发布到他们的问题列表之前我会问这里。