Remove skip on tests that have been fixed.

Guard clause for id_kind in generator

Also move the method to the right class

Fix punctuation [ci skip]

Catch invalid UTF-8 querystring values and respond with BadRequest

FIX: Randomly failing test when running without GIL.

Remove no need `binds.empty?` checking

remove unnecessary readme in dummy application

`README` it is changed to `README.rdoc` in 6b126e23, it has been changed to` README.md` further 89a12c93.

[ci skip] Add more code examples for `Module#anonymous?` docs

`#exec_stmt` is private method and only called in `#exec_query`. it
means `binds` is provided always. No need `binds.empty?` checking.

In later code examples, it is better to write how `Module#anonymous?`
works.

Reason: That one is an Oxford comma, as per our guidelines. See:

     http://edgeguides.rubyonrails.org/api_documentation_guidelines.html#comma

This reverts commit f184cd34.

[ci skip] removed extra comma

[ci skip]

Use sufficient a regexp anchor to check `@response.content_type.to_s`

Refactored association preloader for performance

* less arrays created
* less complexity with only one level of nesting in loop

Change Integer#year to return a Fixnum instead of a Float to improve consistency

This commit follows up of ea9bc06c.
To check `@response.content_type.to_s` is ended with `"xml"`,
to use `\z` is sufficient.

Suppress warnings (warnings about AD::IntegrationTest HTTP request)

These warings have been appeared from
ea9bc06c.

Fix generated projection fields in group by query

* When tried to use `Company#accounts` test/models/company.rb I got:

```
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column:
accounts.company_id: SELECT COUNT(*) AS count_all, "companies"."firm_id"
AS companies_firm_id FROM "companies" INNER JOIN "accounts" ON
"accounts"."company_id" = "companies"."id" GROUP BY "companies"."firm_id"
```

* The refactor on Calculations class was just to simplify the code

Closes #21922

Let `Book(id, author_id)`, `Photo(id, book_id, author_id)` and `Author(id)`

Running `Book.group(:author_id).joins(:photos).count` will produce:

* Rails 4.2 - conflicts `author_id` in both projection and group by:
```sql
SELECT COUNT(*) AS count_all, author_id AS author_id
  FROM "books" INNER JOIN "photos" ON "photos"."book_id" = "books"."id"
 GROUP BY author_id
```

* Master (9d02a25d) - conflicts `author_id` only in projection:
```sql
SELECT COUNT(*) AS count_all, author_id AS author_id
  FROM "books" INNER JOIN "photos" ON "photos"."book_id" = "books"."id"
 GROUP BY "books"."author_id"
```

* With this fix:
```sql
SELECT COUNT(*) AS count_all, "books"."author_id" AS books_author_id
  FROM "books" INNER JOIN "photos" ON "photos"."book_id" = "books"."id"
 GROUP BY "books"."author_id"
```

Remove `#tables` extra args again

This issue was resolved by #21687 already. But re-add args by #18856.
`#tables` extra args was only using by `#table_exists?`. This is for
internal API. This commit will remove these extra args again.

remove unnecessary forwardable require

`Forwardable` has been used in the past

Extract native getter to attr_reader.