Added missing test case for migrations when using sql structure
[ci skip] fix "note" syntax
[ci skip] less derogatory explanation of defaults
[ci skip] add fixture docs link to guides

The fixtures API docs are really comprehensive. We should either be driving people there, or perhaps making fixtures its own guide.
[ci skip] explain association behavior. 

When you manually specify `id:` attribute in a fixture Rails' built in association assignment feature will no longer work. http://stackoverflow.com/questions/23985675/incorrect-association-in-fixtures

This commit raises awareness of this behavior and encourages developers to look directly at the fixture documentation.
[ci skip] remove double "in your"
Restore test deliveries for ActionMailer.
Merge branch 'master' of github.com:rails/docrails
copy edits [ci skip]
Revert "Convert StrongParameters cache to a hash. This fixes an unbounded"

We cannot cache keys because arrays are mutable. We rather want to cache
the arrays. This behaviour is tailor-made for the usage pattern strongs
params is designed for.

In a forthcoming commit I am going to add a test that covers why we need
to cache by value.

Every strong params instance has a live span of a request, the cache goes
away with the object. Since strong params have such a concrete intention,
it would be interesting to see if there are actually any real-world use
cases that are an actual leak, one that practically may matter.

I am not convinced that the theoretical leak has any practical consequences,
but if it can be shown there are, then I believe we should either get rid of
the cache (which is an optimization), or else wipe it in the mutating API.

This reverts commit e63be2769c039e4e9ada523a8497ce3206cc8a9b.
adds a regression test for the strong params converted arrays cache

This is a regression test for 29844dd.
adds some details to the rationale of converted_arrays [ci skip]
Add array support when time zone aware attributes are enabled
Merge pull request #15556 from sgrif/sg-time-zone-aware-arrays

Add array support when time zone aware attributes are enabled
Don't query the database schema when calling `serialize`

We need to decorate the types lazily. This is extracted to a separate
API, as there are other refactorings that will be able to make use of
it, and to allow unit testing the finer points more granularly.
Rename `property` to `attribute`

For consistency with https://github.com/rails/rails/pull/15557
changelog for #15556 and credit @kuldeepaggarwal [Kuldeep Aggarwal]

This is a follow up to #15556

@kuldeepaggarwal did submit this patch way back (#13624).
Correct Example output in Rails guides [ci skip]
Don't rely on `Time.current` in tests

Millisecond inequality causes failures on Travis
Merge pull request #15557 from sgrif/sg-specify-time-zone

Specify a time zone when testing TZ aware attributes