Improve the testing guide [ci skip]

Improve the "Testing Rails Applications" guide adding a section for
testing helpers and a little note about associations with ActiveRecord
and YAML fixtures.

Also add a link to Fixture Builder ; yet another replacement for
fixtures such as Machinist or FactoryGirl.
Remove conditional, since results are always an instance of `ActiveRecord::Result`
Updated guides with latest method [ci skip]

for blank?
fixed file name references [ci skip]
Updated guides with latest method [ci skip]
Removed doc of removed method diff [ci skip]
Fix the SQLite gem name
Add packages list for ArchLinux [ci skip]

Add the packages required on Arch Linux when setting up the development
dependencies
used flat_map instead of map.flatten
Merge pull request #11598 from Karunakar/flat_map1

Used flat_map instead of map.flatten in mas_many_through_associations_test.rb
grab executable from rubygems
Fix order dependent AP test

any_instance.stubs + unstub with Mocha doesn't restore the original status in the following case,
so we need to undef Customer#to_json before every test

require 'test/unit'
require 'mocha/setup'

module M
  def foo() :foo; end
end

class C
  include M

  undef_method :foo
end

C.any_instance.stubs(:foo).returns(:mocha)

C.any_instance.unstub(:foo)
Fix order dependent tests

Reset ActionView::Base.logger after tests
Reset ActionView::Base.logger instead of AC::Base.logger

see: 9b0ac0bc74569db460f87ea6888b3847be0ff5be
Remove $VERBOSE = nil from tasks.rb

Permanently setting $VERBOSE to nil causes unwanted side effects (warnings generated by app code are
silenced when triggered by a rake task but visible otherwise). silence_warnings {} would be safer to
use here since it resets $VERBOSE back to what it was when the block finishes.
Don't mutate the Base settings by merge!ing the given value
Fix order dependent tests

Restore default ActiveSupport::XmlMini.backend after tests
Be sure to restore the default I18n.locale after changed its value in a test
Refactor `ArrayParser`

* Constantize parse token
* Remove extra param passed to `parse_data`
Refactor handling of action normalization

Reference:
Bloody mess internals
http://gusiev.com/slides/rails_contribution/static/#40