we're storing the value in the headers hash, so lets just store the
value in one place.

Modules should be using the API that the abstract modules use so that we
can move these modules between implementations

cookies are always stored as a string in the header hash, so it will not
need to be joined.

eventually we will refactor this to not know about header hashes

Follow up to #21384.

Merge pull request #21384 from jeremyf/updating-ActionController-TestSession-to-behave-as-a-hash-with-indifferent

Updating TestSession to access with indifference

remove require of files under support that do not use

no more require minitest mock here

Rack::Response::Helpers implements this method, so we can safely remove
it

If the response method is defined, then calling `response` will return a
response.

I do not know why files under the support has been require.
However, under the support even rails application does not use.
In addition, since the default under the support file nor is generated, it requires I think not necessary

If AV::Rendering is mixed in, then `rendered_format` will be calculated
based on the current `lookup_context`, but calling `_process_format`
will set the `rendered_format` back on to the same lookup context where
we got the information in the first place!

Instead of getting information from an object, then setting the same
information back on to that object, lets just do nothing instead!

Apparently the AbstractController (whatever "abstract" means) is
expected to work without a request and response.

`render` is the only possible source for the `plain` option.  Pulling
the conditional up to the `render` method removes far away conditionals

We don't need to pass the full hash just to pull one value out.  It's
better to just pass the value that the method needs to know about so
that we can abstract it away from "options"

Since all controller instances are required to have a request and
response object, RackDelegation is no longer needed (we always have to
delegate to the response)

the subclass sets the body on the response object, so we don't need the
superclass doing it too

without this module, the content type is not set correctly

Removed duplicate require 'minitest/mock'

Now that `Controller#status=` just delegates to the response object,
we don't need to set the response on the controller and the response.
We can just set it in one place.

we always have a response object, so there is no reason to test it

these ivars don't exist anymore, so we can remove them from the list

since the controller always has a request on it, we can just ask the
request for the content type.

The controller instance always has an instance of a response object.  We
should store the status code on the response object so that it's only
store in one place.

We always have a response object in controller instances, so we can
remove this conditional

controller instances always have a response object, so we don't need to
test to see if there is one, just always call to_a on the response.

Removed duplicate requires

Use `ActiveRecord::Migration#connection` instead of `@connection`

Fix the unused variable warning

This fixes the following warning.

```ruby
warning: assigned but unused variable - index_definition
```

The following Rails code failed (with a `KeyError` exception) under
test:

```ruby
class ApplicationController < ActionController::Base
  def user_strategy
    # At this point:
    # ```ruby
    # session == {
    #   "user_strategy"=>"email",
    #   "user_identifying_value"=>"hello@world.com"
    # }
    # ```
    if session.key?(:user_strategy)
      session.fetch(:user_strategy)
    end
  end
end
```

When I checked the session's keys (`session.keys`), I got an array of
strings. If I accessed `session[:user_strategy]` I got the expected
`'email'` value. However if I used `session.fetch(:user_strategy)` I
got a `KeyError` exception.

This appears to be a Rails 4.2.4 regression (as the code works under
Rails 4.2.3).

Closes #21383

Fixed to_datetime docs [ci skip]

Controllers should always have a request and response when responding.
Since we make this The Rule(tm), then controllers don't need to be
somewhere in limbo between "asking a response object for a rack
response" or "I, myself contain a rack response".  This duality leads to
conditionals spread through the codebase that we can delete:

  * https://github.com/rails/rails/blob/85a78d9358aa728298cd020cdc842b55c16f9549/actionpack/lib/action_controller/metal.rb#L221-L223