Add `to_json` to `represent` method call

app/controllers/concerns/boards_responses.rb

@@ -69,7 +69,7 @@ module BoardsResponses
   end
 
   def serialize_as_json(resource)
-    serializer.represent(resource)
+    serializer.represent(resource).to_json
   end
 
   def respond_with(resource)

spec/controllers/concerns/boards_responses_spec.rb

@@ -15,9 +15,9 @@ describe BoardsResponses do
     let!(:board) { create(:board) }
 
     it 'serializes properly' do
-      expected = { id: board.id }
+      expected = { "id" => board.id }
 
-      expect(subject.serialize_as_json(board).to_h).to include(expected)
+      expect(JSON.parse(subject.serialize_as_json(board))).to include(expected)
     end
   end
 end