Apply suggestions from code review

Co-authored-by: Phil Pirozhkov <[email protected]>

Author: wata727

lib/rubocop/cop/rails/private_transaction_option.rb

@@ -25,7 +25,7 @@ module Rails
       #   ActiveRecord::Base.transaction(requires_new: true)
       #
       class PrivateTransactionOption < Base
-        MSG = 'Do not use `ActiveRecord::Base.transaction(joinable: _)`.'
+        MSG = 'Use a negated `requires_new` option instead of the internal `joinable`.'
         RESTRICT_ON_SEND = %i[transaction].freeze
 
         # @!method match_transaction_with_joinable(node)

spec/rubocop/cop/rails/private_transaction_option_spec.rb

@@ -1,16 +1,29 @@
 # frozen_string_literal: true
 
 RSpec.describe RuboCop::Cop::Rails::PrivateTransactionOption, :config do
-  it 'registers an offense when using `joinable: false`' do
+  it 'registers an offense when using `ActiveRecord::Base.joinable: false`' do
     expect_offense(<<~RUBY)
-      ActiveRecord::Base.transaction(requires_new: true, joinable: false)
-                                                         ^^^^^^^^^^^^^^^ Do not use `ActiveRecord::Base.transaction(joinable: _)`.
+      ActiveRecord::Base.transaction(requires_new: true, joinable: false) do
+                                                         ^^^^^^^^^^^^^^^ Use a negated `requires_new` option instead of the internal `joinable`.
+        # ...
+      end
+    RUBY
+  end
+
+  it 'registers an offense when using `Account.transaction(joinable: false)`' do
+    expect_offense(<<~RUBY)
+      Account.transaction(requires_new: true, joinable: false) do
+                                              ^^^^^^^^^^^^^^^ Use a negated `requires_new` option instead of the internal `joinable`.
+        # ...
+      end
     RUBY
   end
 
   it 'does not register an offense when using only `requires_new: true`' do
     expect_no_offenses(<<~RUBY)
-      ActiveRecord::Base.transaction(requires_new: true)
+      ActiveRecord::Base.transaction(requires_new: true) do
+        # ...
+      end
     RUBY
   end
 end