rspec test result from csv.read mocking file

I'm using ruby 1.9 and I'm trying to do BDD. My first test 'should read in the csv' works, but the second where I require a file object to be mocked doesn't. Here is my model spec: require 'spec_helper' describe Person do describe "Importing data" do let(:person) { Person.new } let(:data) { "title\tsurname\tfirstname\t\rtitle2\tsurname2\tfirstname2\t\r"} let(:result) {[["title","surname","firstnam