gistfile1.rb

module AutoRollbackBehavior
  def run(runner)
    test_result = nil
    DB.transaction do 
      test_result = super
      raise Sequel::Rollback
    end
    test_result
  end
end

gistfile2.rb

class MiniTest::Spec
  include Rack::Test::Methods
  include AutoRollbackBehavior
end