Add rake test description

No behavior change
Fix changelog indent, remove self from method call in changelog/doc examples

[ci skip]
Refactored nested associations so they are more readable. Added comments
which make it clearer about what's going on.
Merge pull request #9614 from wangjohn/refactoring_nested_associations_for_readability

Refactored nested associations so they are more readable.
Merge pull request #8670 from sanemat/fix/rake-desc

Add rake test description