profile.rb

require 'minitest/autorun'

class FooTest < Minitest::Test
  def self.profile name
    define_method("test_profile_#{name}") do
      # start timer
      10.times { send name }
      # end timer
      if performace_regresses
        flunk "you failed"
      end
    end
  end

  def test_thing
    assert true
  end
  profile :test_thing
end

@tenderlove, finally wrap up everything together: https://github.com/toch/minitest-perf_regression