The "-j" option was added 5 years ago (https://github.com/rails/rails/commit/d9c39c3a)
when we wanted to support prototype-rails and jquery-rails.
Prototype is not as popular and jQuery is not a requirement anymore.
Still the "-j" option can be used to install *any* gem that ends in "-rails".

This "might" open security issues and does not bring great benefits anymore.

If you know which "-rails"-ending gem you want to install, you can manually
add it to the Gemfile just like any other gem.

This is necessary only when updating to Rails 5.0, it is not necessary
for updating to 5.1.

Related #24243

It can not check correctly with `defined?`

```ruby
irb(main):001:0> Rails.application.config.active_record
=> {:maintain_test_schema=>true, :belongs_to_required_by_default=>true}
irb(main):002:0> defined?(Rails.application.config.active_record)
=> nil
```

Follow up to #28469

Instead of forcing new applications to carry an initializer that just
switches things to what their default "should" be, we can handle it
internally.

The initializer is then only used by upgraders: it shows what the new
default would be (commented out), while their upgraded application
continues to operate as it did before.

Under this model, a multiply-upgraded application could accumulate
several new_framework_defaults_*.rb files, for each release series it
has traversed. A given release series only needs to generate the latest,
though, because we don't support `rails app:upgrade` while skipping
releases.

`rails:update` was changed to `app:update` in 6fb31638.
Therefore, I think that it is better that the test name is also `app_update`.

ref this commit seems that has not been merged into 3.7 https://github.com/puma/puma/commit/42bec4600c51ab8a1c1ee5a0e1b738a4ffd82bf2

* Adds test case test
* Adds driver adapter test
* Adds tests for capybara seleium driver (testing the settings not
actually opening the browser to test capybara w/ selenium because that
would so so so slow)
* Adds tests for rack test driver
* Adds tests for generators

When specifying the `pretend` option, expect that no processing will be
done, so do not execute `git init` as well.

* If `--skip-git` is not specified initalize git repo
 when creating new rails app

This reverts commit 8cb3cdff, reversing
changes made to 3bc747bd.

Reason: This test already exists in `SharedGeneratorTests`.
Ref:
https://github.com/rails/rails/blob/master/railties/test/generators/shared_generator_tests.rb#L109..L112
https://github.com/rails/rails/blob/master/railties/test/generators/app_generator_test.rb#L55..L56

- No need to remove bin/yarn separately for API only apps because
  :skip_yarn is set to true for API only apps.
- Added a test for :skip_yarn config.

Follow up to 0d20530e

Move node_modules, package.json, and yarn.lock file to vendor

If `sprockets` is not loaded, `Rails.application.config.assets` is not defined.

Follow up to 92703a9e

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

Related to #26146

Closes #26145

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.