[Fix rubocop#778] Fix a false positive for Rails/DynamicFindBy

Fixes rubocop#778.

This PR fixes a false positive for `Rails/DynamicFindBy`
when using `page.find_by_id` as a Capybara testing API.
This default setting emphasizes suppressing false positive over false negative.

Author: koic

changelog/fix_false_positive_for_rails_dynamic_find_by.md

@@ -0,0 +1 @@
+* [#778](https://github.com/rubocop/rubocop-rails/issues/778): Fix a false positive for `Rails/DynamicFindBy` when using `page.find_by_id` as a Capybara testing API. ([@koic][])

config/default.yml

@@ -352,6 +352,7 @@ Rails/DynamicFindBy:
     - find_by_sql
   AllowedReceivers:
     - Gem::Specification
+    - page # Prevents a warning for `page.find_by_id`. See: https://github.com/rubocop/rubocop-rails/issues/778
 
 Rails/EagerEvaluationLogMessage:
   Description: 'Checks that blocks are used for interpolated strings passed to `Rails.logger.debug`.'

lib/rubocop/cop/rails/dynamic_find_by.rb

@@ -29,12 +29,14 @@ module Rails
       #   # good
       #   User.find_by_sql(users_sql)
       #
-      # @example AllowedReceivers: ['Gem::Specification'] (default)
+      # @example AllowedReceivers: ['Gem::Specification', 'page'] (default)
       #   # bad
       #   Specification.find_by_name('backend').gem_dir
+      #   page.find_by_id('a_dom_id').click
       #
       #   # good
       #   Gem::Specification.find_by_name('backend').gem_dir
+      #   page.find_by_id('a_dom_id').click
       class DynamicFindBy < Base
         include ActiveRecordHelper
         extend AutoCorrector