Allow authentication header to not have to specify 'token=' key.

Fixes: https://github.com/rails/rails/issues/17108.
Correct test description for large integer test
[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.
Simplify rake test vs rake test:all

Renames `rake test:all` to `rake test` by changing old `rake test:run` to previous version of `rake test:all`.  Removes old definition of `rake test`. Also renames `rake test:all:db` to `rake test:db` and deprecates `rake test:all` & `rake test:all:db`
Replace "behaviour" with "behavior"

Update to consistently use American English [ci skip]
Merge pull request #17588 from djpowers/patch-1

[ci skip] Use American English and replace "behaviour" with "behavior".
Fix Rails::Paths::Path.unshift interface
Merge pull request #17348 from DavidGeukers/rake_test_all

simplify rake test vs rake test:all
Follow the coding conventions
Merge pull request #17596 from aderyabin/follow_convension

Follow the coding conventions
Merge pull request #17593 from igas/paths-unshift-arity

Fix Rails::Paths::Path.unshift interface
Improve railties changelog entry and move latest to the top [ci skip]
Abstract encoding strategy for ActiveSupport::MessageVerifier
Allow habtm class_name option to be consistent with other associations
Merge pull request #17604 from rymohr/message-verifier-case-sensitivity

Abstract encoding strategy for ActiveSupport::MessageVerifier
[ci skip] Add one more example to routing testing, and highlight association
name keywords
Merge branch 'sandipransing-master'
[ci skip] Capybara added to other testing approaches
Merge pull request #17612 from sandipransing/testing-guide

[ci skip] Capybara added to other testing approaches