add include_hidden option to collection_check_boxes helper
Minor grammer, code conventions fix [ci skip]

Conflicts:
	activesupport/lib/active_support/core_ext/hash/conversions.rb
Merge pull request #14394 from zoltankiss/fix_typo

Minor grammer, code conventions fix [ci skip]
Fix MailerPreview broken tests

`BaseMailerPreview.welcome` is an instance method, so we need to stub the
method on a instance level and not on Class. The stub is important to make
sure the Message object is the same in the other expectations.
This was working randomly because Mocha uses == to compare two objects
on the `with()` expectation and even if the Mail::Message objects were
not the same object they are equal, but thats not the case in 100% of
the runs. So we need to make sure we use `.any_instance` method and have
the right message object.
Merge pull request #12662 from nashby/include-hidden-collection

add include_hidden option to collection_check_boxes helper

Conflicts:
	actionview/CHANGELOG.md
	actionview/test/template/form_collections_helper_test.rb
Merge pull request #14395 from arthurnn/fix_mailer_preview_test

Fix MailerPreview broken tests
Reword 5.6 strong parameters and private method stuff [ci skip]
Merge pull request #14396 from afshinator/master

Reword 5.6 strong parameters and private method stuff [ci skip]
Extend fixture label replacement to allow string interpolation

Allows fixtures to use their $LABEL as part of a string instead
of limiting use to the entire value.

    mark:
      first_name: $LABEL
      username: $LABEL1973
      email: $LABEL@$LABELmail.com

    users(:mark).first_name # => mark
    users(:mark).username   # => mark1973
    users(:mark).email      # => mark@markmail.com
Merge pull request #14399 from genericsteele/fixture-label-string-interpolation

Extend fixture label replacement to allow string interpolation
Let COMMAND_WHITELIST be an Array, not a String
Remove extra white-spaces [ci skip]

Follow up to 024e5e31
Use nested_scope? not shallow? to determine whether to copy options

The method `shallow?` returns false if the parent resource is a singleton so
we need to check if we're not inside a nested scope before copying the :path
and :as options to their shallow equivalents.

Fixes #14388.
Avoid concurrent test collision on the same memcache server by namespacing keys
Add an explicit require for 4ece124396669d3580e7f229ab407a0d4882727a rather than assume SecureRandom is available