Ruby on Rails

Is there a way to make Rails.cache.fetch always execute the code block
in the test environment?  (disable caching)

For example in my test console on Rails 3

ruby-1.9.2-rc2 > Rails.cache.fetch('foo') {'bar'}
 => "bar"
ruby-1.9.2-rc2 > Rails.cache.fetch('foo') {'bar44'}
 => "bar"

Caching is on.  Using filestore

ruby-1.9.2-rc2 > Rails.cache
 => #<ActiveSupport::Cache::FileStore

Is there a ActiveSupport::Cache::Store implementation that doesn't
cache?   I'm assuming I'm just missing something trivial since this is
easily disabled for page/action/fragment caching with

config.action_controller.perform_caching = false

I have...
ruby-1.9.2-rc2 >
Rails.application.config.action_controller.perform_caching
 => false

What am I missing?  Thanks
Tony