When writing rspec tests, it's preferable to use `let` blocks instead of instance variables. `let` blocks (https://www.relishapp.com/rspec/rspec-core/v/2-13/docs/helper-methods/let-and-let) offer a similar role but are guaranteed to be local to each test which helps prevent leakage across tests. http://stackoverflow.com/questions/5359558/when-to-use-rspec-let gives a little bit more information on instance variables vs `let`.