widget.rb

class Widget
  class << self
    protected
    def define_attribute(name)
      attr_accessor name
    end
  end
  
  define_attribute :name
  
  def initialize(name)
    @name = name
  end
end

widget_test.rb

require "minitest"
require "minitest/autorun"

class WidgetTest < Minitest::Test
  def setup
    @subject = Widget.new("foo")
  end
  
  def test_name_is_public
    assert_equal @subject.name, "foo" # NoMethodError: protected method `name' called for #<Widget:0x7920ba90 @name="foo">
  end
end