Onf of the sides can be nil and it will raise a Conversion error

test for regression introduced by https://github.com/rails/rails/pull/9155

The previous regex was allowing `_` in the URI scheme, which is not
allowed by RFC 3986. This change brings the regex in line with the RFC.

In some instances, `assert_redirected_to` assertion was returning an
incorrect and misleading failure message when the assertion failed.
This was due to a disconnect in how the assertion computes the redirect
string for the failure message and how `redirect_to` computes the
string that is actually used for redirection.

I made the `_compute_redirect_to_loaction` method used by `redirect_to`
public and call that from the method `assert_redirect_to` uses to
calculate the URL.

The reveals a new test failure due to the regex used by
`_compute_redirect_to_location` allow `_` in the URL scheme.

Previously it was raising a NilException

This gem is used by Active Support but it should not be a dependency of
Action Pack.

HelperyTestHelper was introduced in 66ef9227 by @josevalim
to pair with HelperyTestController. This test controller was
later removed in e10a2531 by @strzalek, leaving HelperyTestHelper unused

[ci skip]

This reverts commit ab5cd54b, reversing
changes made to cdc10c89.

Reason: This way of defining root path is still supported. See
https://github.com/rails/rails/blob/d262773ab7f0aae5de2d354ac2eca168e95b653d/actionpack/test/controller/routing_test.rb#L450-457

see: 9b0ac0bc

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

The fixture for module AbcHelper defines three functions bare_a,
bare_b and bare_c, but only bare_a is used in the code that tests
helper functions.

The documentation in this section is referring to a profile,
so the resource that's created should probably also be a
profile of some sort.

The docs refference a blacklist, but really what's being described
is a whitelist. Anything that matches the constraint gets through to
the path.

closes #12149

The methods:

 * #render_to_body
 * #render_to_string
 * #_normalize_render

Haven't had anything specyfic to ActionView. This was common code which should belong to AbstractController

This reverts commit 7de994fa.