Testing the difference between ActiveSupport::SafeBuffer#gsub! and String#gsub!

README.md

Testing ActiveSupport::SafeBuffer#gsub!

Although ActiveSupport::SafeBuffer#gsub! appears to work, its behaviour differs from String#gsub!.

These tests show how ActiveSupport::SafeBuffer#gsub! doesn't update Regexp.last_match.

Gemfile

source 'https://rubygems.org'

gem 'activesupport'
gem 'minitest'

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    activesupport (4.2.2)
      i18n (~> 0.7)
      json (~> 1.7, >= 1.7.7)
      minitest (~> 5.1)
      thread_safe (~> 0.3, >= 0.3.4)
      tzinfo (~> 1.1)
    i18n (0.7.0)
    json (1.8.3)
    minitest (5.7.0)
    thread_safe (0.3.5)
    tzinfo (1.2.2)
      thread_safe (~> 0.1)

PLATFORMS
  ruby

DEPENDENCIES
  activesupport
  minitest

BUNDLED WITH
   1.10.4

testing-activesupport-safe-buffers-and-gsub.rb

require 'bundler/setup'

require 'minitest/autorun'
require 'active_support'

class RegexpTest < Minitest::Test
  def test_behaviour_of_active_support_safe_buffer_and_gsub_bang
    string = ActiveSupport::SafeBuffer.new('Hello world')

    string.gsub!('ll') do |match|
      match.upcase
    end

    assert_equal 'HeLLo world', string
    assert_equal nil, Regexp.last_match # I'd expect this to contain a MatchData object, as it does for String#gsub!
  end

  def test_behaviour_of_strings_and_gsub_bang
    string = 'Hello world'

    string.gsub!('ll') do |match|
      match.upcase
    end

    assert_equal 'HeLLo world', string
    assert_equal 1, Regexp.last_match.length
    assert_equal 'll', Regexp.last_match[0]
  end
end