get tested_class in rails test

article_test.rb

require 'test_helper'

class ArticleTest < ActiveSupport::TestCase
  test 'tested_class is Article' do
    assert_same Article, tested_class
  end
  
private

  def tested_class
    @tested_class ||= begin
      /(?<klass>.+)Test/ =~ self.class.name
      klass.constantize
    end
  end
end