gistfile1.rb

#!/usr/bin/env ruby
# encoding: utf-8

require 'minitest/autorun'
require 'nokogiri'

class MyEncodingTest < MiniTest::Unit::TestCase

  def test_replace_document
    doc = Nokogiri::HTML('<p>abc</p>')
    doc.inner_html = '<p>…</p>'
    assert_equal '<p>…</p>', doc.inner_html
  end

  def test_replace_fragment
    original_string = '<div><p>abc</p></div>'
    replaced_string = '<div><p>…</p></div>'
    replacement_string = '<p>…</p>'

    doc = Nokogiri::HTML.fragment(original_string, 'UTF-8')
    assert_equal Encoding.find('UTF-8'), doc.inner_html.encoding # works

    doc.css('div').first.inner_html = replacement_string
    assert_equal Encoding.find('UTF-8'), doc.inner_html.encoding # works
    assert_equal replaced_string, doc.inner_html # FAILS
  end

end