I am partial to RSpec, but this is a well-reasoned argument for using Minitest.
Great post on using Hashes, OpenStruct, value objects and Hashie and the performance implications. Schneems is clearly opinionated and find fault with a very popular library. In his style, though he actually does something about it. He has a pull-request to change the underlying implementation and started a discussion with the library mantainers.
The title says it all. Well written and explained. Definetly a worthy tool to have availbale when optimizing performance.