test for namespaced associations + bug fixed

test/unit/active_model/serializer/associations/build_serializer_test.rb

@@ -7,6 +7,7 @@ module ActiveModel
         def setup
           @association = Association::HasOne.new('post', serializer: PostSerializer)
           @post = Post.new({ title: 'Title 1', body: 'Body 1', date: '1/1/2000' })
+          @user = User.new
         end
 
         def test_build_serializer_for_array_called_twice
@@ -15,6 +16,20 @@ module ActiveModel
             assert_instance_of(PostSerializer, serializer)
           end
         end
+
+        def test_build_serializer_from_in_a_namespace
+          assoc      = Association::HasOne.new('profile')
+          serializer = TestNamespace::UserSerializer.new(@user).build_serializer(assoc)
+
+          assert_instance_of(TestNamespace::ProfileSerializer, serializer)
+        end
+
+        def test_build_serializer_with_prefix
+          assoc      = Association::HasOne.new('profile', prefix: :short)
+          serializer = UserSerializer.new(@user).build_serializer(assoc)
+
+          assert_instance_of(ShortProfileSerializer, serializer)
+        end
       end
     end
   end