minitest.rake

task :minitest do
  path = File.expand_path('test', Rails.root)
  require File.expand_path('test_helper', path)
  Dir[path + '/*_test.rb'].each do |file|
    require file
  end
end

posts_controller_test.rb

class TestSumthin < Okonski::Tests::ControllerCase
  tests PostsController

  def test_index
    get :index
    assert_response :success
    assert_template :index
    refute_empty assigns(:posts)
  end
end

test_helper.rb

require 'minitest/autorun'

ENV['RAILS_ENV'] = 'test'

require File.expand_path('../../config/environment', __FILE__)

require 'active_support/testing/setup_and_teardown.rb'
module Okonski
  module Tests
    class Case < MiniTest::Unit::TestCase
      include ActiveSupport::Testing::SetupAndTeardown
      include ActiveSupport::Testing::SetupAndTeardown::ForMiniTest

      def build_message(head, template=nil, *arguments)
        template &&= template.chomp
        template.gsub(/\?/) { mu_pp(arguments.shift) }
      end
    end

    class ControllerCase < Case
      include Rails.application.routes.url_helpers
      include ActionController::TestCase::Behavior

      def setup
        @routes = Rails.application.routes
      end
    end
  end
end