shared_example.rb

class MiniTest::Spec
  def self.shared_examples
    @shared_examples ||= {}
  end
end

module MiniTest::Spec::SharedExamples
  def shared_examples_for(desc, &block)
    MiniTest::Spec.shared_examples[desc] = block
  end

  def it_behaves_like(desc)
    self.instance_eval do
      MiniTest::Spec.shared_examples[desc].call
    end
  end
end

Object.class_eval { include(MiniTest::Spec::SharedExamples) }