[Testing guide] Use "Fixtures API" instead of "fixture api".
[Testing guide] Using "Fixtures API" consistently

- In guides, "API" is used consistently instead of "api".
- Reason behind replacing "fixtures API" to "Fixtures API" is because
  here we are referring to the concept of "fixtures". In other places in
  the guide "fixture" OR "fixtures" is referred to the single or
  multiple instances of test data.
- This is also followup of https://github.com/rails/docrails/commit/aa9d1332b20305dd860b21a7ada06c5252bebad5#commitcomment-8497376.
Fix grammar on ActiveRecord::AttributeMethods doc.

[ci skip]
allow 'all' for :domain option in addition to :all
Don't remove mailer layouts files
Remove custom errors page section from the guides

This pattern is too problematic and introduces a lot of edge cases:

  * On 4.2, the issue https://github.com/rails/rails/issues/15124 is
    back again.
  * needs to define each action for each http status otherwise the
    router raises ActionController::RoutingError (No route matches).
  * If the router has `match "/*username",...` and some action is
    missing, Rails will pick up the "match" and try to do its job.
  * encourages people to copy & paste programming. Not DRY.

[ci skip]
Fix Sidekiq ActiveJob integration setup

* .connect on a Redis connection wasn't valid
* Reset logger after we're done testing for redis connection to avoid
  "closed stream" error when starting server for real from a fork
Hide potentially sensitive ActiveJob params from logs

* Show GlobalID instead of full object .inspect output
Merge branch 'master' of github.com:rails/rails
Only filter GIDable objects; remove cosmetic changes
Add `#verified` and `#valid_message?` to MessageVerifier

This commit adds a `#verified` method to
`ActiveSupport::MessageVerifier` which will return either `false` when
it encounters an error or the message. `#verify` continues to raise an
`InvalidSignature` exception on error.

This commit also adds a convenience boolean method on `MessageVerifier`
as a way to check if a message is valid without performing the
decoding.
Silence Minitest for plugin tests.

Fixes https://github.com/rails/rails/issues/17340.

Use Minitest::BacktraceFilter instead of removing all silencers. This
will allow the backtrace for all libraries in the plugin to be shown
while removing noise generated by Minitest's backtrace.
Allow failures for mysql adapter tests
Merge pull request #17862 from lucasmazza/lm-hide-action

`_generate_paths_by_default` should always be private.
Merge pull request #17867 from tgxworld/silence_minitest_plugins

Silence Minitest for plugin tests.
Merge pull request #17727 from lleger/lleger-add-methods-to-message-verifier

Add new methods to MessageVerifier
Refactor debug view
Avoid logic in ERB and use helpers
Merge pull request #17873 from kirs/refactor-debug-erb

Refactor debug view
Prefer object/nil over `true`/`false`

This is the project guideline and the reasons are:

* That follows standard Ruby semantics.
* Allows the implementation to avoid artificial code like !! or something ? true : false
* You do not need to rely on the exact type of 3rd party code. For
example, if your method returns str.end_with?('foo') you do not need to
make sure end_with? returns a singleton. Your predicate just propagates
predicate semantics up regardless of what end_with? returns.
Allow to unscope where conditions using `arel_table` with Symbol

This commit fixes the following case.

    User.where(User.arel_table[:created_at].lteq(1.year.ago)).unscope(where :created_at)