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`
Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs [ci skip]

Added SanitizeHelper to rails guide docs update [ci skip]
Creating an SSE class to be used with ActionController::Live.
Rails.logger should have level specified by config.log_level. 

Fix bug when log level of Rails.logger (which was set via config.logger) does not match the    config.log_level.
fix tests
update guide to reflect default HMAC SHA1 in MessageVerifier used in SignedCookieStore [ci skip]
remove language about configuring digest method [ci skip]
Minor optimization and code cleanup in query_methods.

- Use symbols rather than strings where possible to avoid extra object construction
- Use destructive methods where possible to avoid extra object construction
- Use array union rather than concat followed by uniq
- Use shorthand block syntax where possible
- Use consistent multiline block styles, method names, method parenteses style, and spacing
Add timeout to test_async_stream

Without timeout:
this test executed infinitely on JRuby
Passes on MRI

With Timeout:
this test gracefully fails on JRuby
Passes on MRI, tested on v2.0 & v1.9.3
Added Action View in 'rake about' [ci skip]
Fix jruby warning when capture calls unlink on an open tempfile

Jruby cannot unlink a tempfile unless it is closed first.
Merge pull request #11725 from atambo/jruby_capture_unlink

Fix jruby warning when capture calls unlink on an open tempfile
Merge pull request #11721 from gaurish/join-timeout

Add timeout to test_async_stream
add a test for concat on hm:t associations
Isolate railties Generators Tests

With this change jruby should pass all of the railties tests.
Merge pull request #11726 from atambo/isolate_generator_tests

Isolate railties Generators Tests
Revert "Isolate railties Generators Tests"

This fixes railties tests in JRuby but break it in MRI
This reverts commit fea99276c7024f183bf72a16ad9f36af4bae1d42.
use flat_map
Updated the guide to say that the localisation file for validation messages is in activemodel, not activerecord