ApplicationRecord documentation pass

This is a pass over the documentation which fills the missing gaps of
`ApplicationRecord`.

[ci skip]

1 files changed, 1 insertions, 1 deletions

diff --git a/guides/source/testing.md b/guides/source/testing.md
index 58524fd6c5..a4b62955c5 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -177,7 +177,7 @@ Saved the article without a title
 Now to get this test to pass we can add a model level validation for the _title_ field.
 
 ```ruby
-class Article < ActiveRecord::Base
+class Article < ApplicationRecord
   validates :title, presence: true
 end
 ```