Since using a browser is only for selenium it doesn't really make sense
to have a separate class for handling it there. This brings a lot of the
if/else out of the main SystemTestCase class and into the Driver class
so we can abstract away all that extra work.

[ci skip]

[ci skip]

Since `ActionController:Parameters` does not inherit `Hash`, need to
explicitly convert it to `Hash`.
Also, `Parameters#to_h` returns `Hash` whose key is `String`. Therefore,
if merge as it is, the value will not be overwritten as expected.

```diff
diff --git a/actionpack/lib/action_controller/metal/redirecting.rb b/actionpack/lib/action_controller/metal/redirecting.rb
index a3159c29dd..1836a07d4e 100644
--- a/actionpack/lib/action_controller/metal/redirecting.rb
+++ b/actionpack/lib/action_controller/metal/redirecting.rb
@@ -50,8 +50,8 @@ module Redirecting
     #   redirect_to post_url(@post), status: 301, flash: { updated_post_id: @post.id }
     #   redirect_to({ action: 'atom' }, alert: "Something serious happened")
     #
-    # Statements after redirect_to in our controller get executed, so redirect_to doesn't stop the execution of the function.
-    <U+2028># To terminate the execution of the function immediately after the redirect_to, use return.
+    # Statements after +redirect_to+ in our controller get executed, so +redirect_to+ doesn't stop the execution of the function.
+    # To terminate the execution of the function immediately after the +redirect_to+, use return.
     #   redirect_to post_url(@post) and return
     def redirect_to(options = {}, response_status = {})
       raise ActionControllerError.new("Cannot redirect to nil!") unless options
```

https://travis-ci.org/rails/rails/jobs/207908041#L549

This reverts commit 84c1b107.

Reverted #28283 so reverted it's changelog update as well.

This reverts commit 0d73f911, reversing
changes made to 21ff8a49.

We don't want to silence Puma because it's start up messages can be
useful (to see threads, port etc). #28109 was instead fixed by not
running system tests by defaul with `bin/rails test` in #28286.

Should be `ActionController::ParameterMissing` and not
`ActionController::MissingParameter`.

Corresponding change was done in guides in
https://github.com/rails/rails/pull/9816.

Fixes #28109

`Capybara::RackTest::Driver` does not support taking screenshots. If call
`#save_screenshot` on `Capybara::RackTest::Driver` will raise the error.

```ruby
Error:
UsersTest#test_visiting_the_index:
Capybara::NotSupportedByDriverError: Capybara::Driver::Base#save_screenshot
```

To prevent errors, if driver does not support screenshot, do not call it.

If application has ajax, browser may begin request after rollback.
`teardown_fixtures` will be called after `super` on `after_teardown`
so we must call `Capybara.reset_sessions!` before `super`

https://github.com/rails/rails/blob/b61a56541aecd7ac685d4f19d943177a3f1b465a/activerecord/lib/active_record/fixtures.rb#L857

Now reset the driver before take failed screenshot since #28144.
However, I think that failed screenshot should be take with the driver
actually used in the test.
So, fixed to take screenshot before reset driver.

In ca324a0d the flash middleware was effectively removed by its
constructor returning the app it was passed and the `commit_flash`
call was moved to the `ActionController::Metal#dispatch` method.
This broke any redirect routes that modified the flash because the
redirect happens before `dispatch` gets called.

To fix it, this commit adds a `commit_flash` call in the `serve`
method of `ActionDispatch::Routing::Redirect`.

Fixes #27992.

A gzip file has a checksum and length for the decompressed data in its
footer which isn't checked by just calling Zlib::GzipReader#read.
Calling Zlib::GzipReader#close must be called after reading to the end
of the file causes this check to be done, which is done by
Zlib::GzipReader.wrap after its block is called.

Previously, `driven_by` would change the Capybara configuration when
the test case is loaded, and having multiple test classes with different
`driven_by` configs would fail as the last loaded would be effective.

The documentation needs to be above the method to correctly document the
method.

Also correct use of `direct class:` to `resolve` in example.

Since a `direct` url helper block is evaluated using `instance_exec`
then methods that are available in the instance context can be
accessed, e.g. the params object in a controller action or view.

This wasn't clear from the example so expand on that point and add
a test case for this situation.

Further missing requires for Timeout exposed due to Bundler 1.14.5

Use double quoted strings, come down hard on some typos.

[ci skip]

Use a separate method called `resolve` for the custom polymorphic
mapping to clarify the API.

Using `undef_method` means that when a route is removed any other
implementations of that method in the ancestor chain are inaccessible
so instead use `remove_method` which restores access to the ancestor.