Document JoinTable migration generator
Update documentation for yml usage

Update documentation for yml usage against https://github.com/rails/rails/issues/8612
Update guides/source/layouts_and_rendering.md

Removed first slash. The subdirectory will nto be found with slash befor it.

fixed inconsistent `require 'test_helper'` in testing guide
Update guides/source/rails_on_rack.md

Rack::Lock actually sets rack.multithread to `false`, not `true`.

Presumably because once inside the mutex, the app can function as if it were single threaded.
Fix usage of lambda as a Rack endpoint

The response body needs to respond_to? :each.
Revert "minitest provides "it" and "describe""

This reverts commit 22bc12ec374b8bdeb3818ca0a3eb787dd3ce39d8.

REASON: We will remove the MiniTest::Spec from Rails and we need these
methods again

Conflicts:
	activesupport/lib/active_support/test_case.rb
Inherit from MiniTest::Unit::TestCase instead of MiniTest::Spec
Add active_support/testing/autorun

minitest/autorun load minitest/spec polluting the global namespace with
the DSL that we don't want on Rails
Remove unneeded tests

These tests are needed only if we are using MiniTest::Spec
Do not use the same tests description
Alias refute methods to assert_not and perfer assert_not on tests
Add note on the contributing guide to not use the refute methods
Merge branch 'minitest_cleanup'
Merge pull request #8666 from mekishizufu/fix_lambdas

Fix usage of lambda as a Rack endpoint
Do not install debugger in the pathlevel 362
Use ActiveSupport::TestCase in the journey tests
refatctoring of some code repetition in spawn_methods
Revert "Do not install debugger in the pathlevel 362"

This reverts commit 9c18b6a818801a77a90c2768e436e4690537a3ab.
Merge pull request #8664 from acapilleri/spawn_method

refatctoring of some code repetition in spawn_methods