tests and docs updates

Author: stefannibrasil

lib/shoulda/matchers/active_record/association_matcher.rb

@@ -1012,7 +1012,7 @@ def have_delegated_type(name)
       # ##### deprecated
       #
       # Use `deprecated` to assert that the `:deprecated` option was specified.
-      # (Rails 8.1+).
+      # (Enabled by default in Rails 8.1+)
       #
       #     class Player < ActiveRecord::Base
       #       has_many :games, deprecated: true
@@ -1643,11 +1643,11 @@ def join_table(join_table_name)
         end
 
         def deprecated(deprecated = true)
-          if Rails::VERSION::STRING >= '8.1'
+          if ::ActiveRecord::VERSION::STRING >= '8.1'
             @options[:deprecated] = deprecated
             self
           else
-            raise NotImplementedError, "`deprecated` association matcher is only available on Rails version >= 8.1."
+            raise NotImplementedError, "`deprecated` association matcher is only available on Active Record >= 8.1."
           end
         end
 

spec/unit/shoulda/matchers/active_record/association_matcher_spec.rb

@@ -6,9 +6,11 @@
   if rails_version <= 8.1
     context "using the deprecated matcher" do
       it 'raises a NotImplementedError' do
+        message = "`deprecated` association matcher is only available on Active Record >= 8.1."
+
         expect do
           expect(having_many_children(deprecated: false)).to have_many(:children).deprecated(false)
-        end.to fail_with_message("hello")
+        end.to fail_with_message(message)
       end
     end
   end