We will no longer cover every single file that is loaded by Rails, as
this would be too difficult and time consuming to maintain.

We also expect the reader to know about rails server at this point.

* Moved the simplest case--enable/disable all on all--to the top.
* Made clear what "ORM" means to avoid having to teach people how to solve "uninitialized constant ORM"
  errors in their test reports.

bundle exec is needed even if running a single test.

Updated guide to say Rails 4.0 requires 1.9.3 or higher, not Rails 3.2.

a test case that ensures AR::Relation#merge can merge associations

just a consolidation of the changelogs with minimal formatting

[ci skip]

This reverts commits 911a0859 and
30b31f51.

Reason: these changes make the Active Model tests fail randomly.

Some examples:
http://travis-ci.org/#!/rails/rails/jobs/1498992
http://travis-ci.org/#!/rails/rails/jobs/1496948
http://travis-ci.org/#!/rails/rails/jobs/1489985

This script was used to reproduce these breaks:
https://gist.github.com/f6828a03ee4d40bffbc3

200 times, 0 failures

Similarly to 65250022, this allows to use routes helpers for mounted
helpers, but this time in ActionView::TestCase

Correct the use of to_model in polymorphic routing

In integration tests, you might want to use helpers from engines that
you mounted in your application. It's not hard to add it by yourself,
but it's unneeded boilerplate. mounted_helpers are now included by
default. That means that given engine mounted like:

    mount Foo::Engine => "/foo", :as => "foo"

you will be able to use paths from this engine in tests this way:

    foo.root_path #=> "/foo"

(closes #6573)

remove unneeded blank line from !namespeced? generated controllers

Revert "Only include Rake::DSL if it's defined."

improve readability of AR explain result