serialized Type should delegate `type_cast_for_write` to underlying Type

This adds a regression test for #14411, which was fixed by #15503.

Closes #14411
Closes #14595

activerecord/lib/active_record/type/serialized.rb

@@ -20,7 +20,7 @@ def type_cast(value)
       def type_cast_for_write(value)
         return if value.nil?
         unless is_default_value?(value)
-          coder.dump(value)
+          super coder.dump(value)
         end
       end
 

activerecord/test/cases/adapters/postgresql/hstore_test.rb

@@ -294,6 +294,41 @@ def test_update_all
       Hstore.update_all tags: { }
       assert_equal({ }, hstore.reload.tags)
     end
+
+    # FIXME: remove this lambda once `serialize` no longer issues a db connection.
+    LAZY_MODELS = lambda do
+      return if defined?(TagCollection)
+
+      class TagCollection
+        def initialize(hash); @hash = hash end
+        def to_hash; @hash end
+        def self.load(hash); new(hash) end
+        def self.dump(object); object.to_hash end
+      end
+
+      class HstoreWithSerialize < Hstore
+        serialize :tags, TagCollection
+      end
+    end
+
+    def test_hstore_with_serialized_attributes
+      LAZY_MODELS.call
+      HstoreWithSerialize.create! tags: TagCollection.new({"one" => "two"})
+      record = HstoreWithSerialize.first
+      assert_instance_of TagCollection, record.tags
+      assert_equal({"one" => "two"}, record.tags.to_hash)
+      record.tags = TagCollection.new("three" => "four")
+      record.save!
+      assert_equal({"three" => "four"}, HstoreWithSerialize.first.tags.to_hash)
+    end
+
+    def test_clone_hstore_with_serialized_attributes
+      LAZY_MODELS.call
+      HstoreWithSerialize.create! tags: TagCollection.new({"one" => "two"})
+      record = HstoreWithSerialize.first
+      dupe = record.dup
+      assert_equal({"one" => "two"}, dupe.tags.to_hash)
+    end
   end
 
   private