I'm a fan of MiniTest::Spec. It strikes a nice balance between the simplicity of TestUnit and the readable syntax of RSpec. When I first switched from RSpec to MiniTest::Spec, one thing I was worried I would miss was the ability to add matchers. (A note in terminology: "matchers" in MiniTest::Spec refer to something completely different than "matchers" in RSpec. I won't get into it, but from now on, let's use the proper term: "expectations").

Understanding MiniTest::Expectations

Let's take a look in the code (I'm specifically referring to the gem, not the standard library that's built into Ruby 1.9):

# minitest/spec.rb

module MiniTest::Expectations