If you're in the default testing environment your rails cache is ActiveSupport::Cache::NullStore which will always succeed but it doesn't actually store or return anything. There's an almost completely undocumented method called with_local_cache on NullStore that lets you run a block with a MemoryStore instead of a NullStore for the duration of the block. This happens because it prepends the ActiveSupport::Cache::Strategy::LocalCache class. This lets you test one or two things that require caching without enabling it on all tests and slowing everything down.