remove unnecessary require and extend

Suppress warnings

remove old links from debugging guide [ci skip]

`rack/test` is require at the top of file.
https://github.com/rails/rails/blob/master/railties/test/railties/engine_test.rb#L3

In addtion, `Rack::Test::Methods` is include in class, extend is unnecessary.
https://github.com/rails/rails/blob/master/railties/test/railties/engine_test.rb#L9

This commit suppressed
`warning: instance variable @session_store not initialized`.
e5a6f7ee introduced these
warnings.

Revert "Adds `not_in?` onto Object"

Reset rack.input when the environment is scrubbed for the next request

`FinderMethods` uses `records` (`load_target`) when `loaded?` is true

Fix to `CollectionProxy#load` does `load_target`

Remove `prepare_binds_for_database` internal method

Prevent `table_comment` query if a table doesn't have a comment

Avoid calling `current_database` in `table_comment`

`@quoted_{column,table}_names` should cache a frozen string

`current_database` executes a query and `table_comment` is called to all
tables even if a table does not have a comment. Using `current_database`
increases extra queries.

Caching a mutable string causes the following issue.

```
Loading development environment (Rails 5.1.0.alpha)
irb(main):001:0> ActiveRecord::Base.connection.quote_table_name('foo') << '!!'
=> "`foo`!!"
irb(main):002:0> ActiveRecord::Base.connection.quote_table_name('foo') << '!!'
=> "`foo`!!!!"
irb(main):003:0> ActiveRecord::Base.connection.quote_table_name('foo') << '!!'
=> "`foo`!!!!!!"
```

To avoid relying on the connection adapter for type casting binds.

[ci skip] Add documentation for error using select with order

Fix accessing provider_job_id inside active jobs for sidekiq adapter

Updated getting_started.md guide source text to reflect the change in error message …

See https://github.com/nex3/rb-inotify/pull/49

Correctly return `associated_table` when `associated_with?` is true

[Rafael Mendonça França + Takeshi AKIMA]

Remove circular join references in join_dependency

Add rationale for checking auth_tag length for AEAD ciphers

Fix keyed defaults with root

Decouple statement cache from connection adapter

Fixes #25653.

Updated getting_started guide to reflect the change in error message for ActionController::UnknownFromat in ArticlesController#new

Restored texts about XML and JS template handlers. [ci skip]

Before this change, posted parameters would leak across requests. The included
test case failed like so:

      1) Failure:
    TestCaseTest#test_multiple_mixed_method_process_should_scrub_rack_input:
    --- expected
    +++ actual
    @@ -1 +1 @@
    -{"bar"=>"an bar", "controller"=>"test_case_test/test", "action"=>"test_params"}
    +{"foo"=>"an foo", "bar"=>"an bar", "controller"=>"test_case_test/test", "action"=>"test_params"}

An argument could be made that this situation isn't encountered often and that
one should limit the number of requests per test case, but I still think the
parameter leaking is an unexpected side-effect.

Add rationale for manually checking auth_tag length, which got lost when #25874 was squashed before merging [skip ci]

Add an assertion to the tests that should be loaded the target.

Quoting booleans should return a frozen string