Consolidate JSON parsing in serializers specs (#27693)

spec/controllers/emojis_controller_spec.rb

@@ -8,13 +8,11 @@ describe EmojisController do
   let(:emoji) { Fabricate(:custom_emoji) }
 
   describe 'GET #show' do
-    subject(:body) { JSON.parse(response.body, symbolize_names: true) }
-
     let(:response) { get :show, params: { id: emoji.id, format: :json } }
 
     it 'returns the right response' do
       expect(response).to have_http_status 200
-      expect(body[:name]).to eq ':coolcat:'
+      expect(body_as_json[:name]).to eq ':coolcat:'
     end
   end
 end