Change validation scope and Fix tests

spec/models/vote_spec.rb

@@ -8,12 +8,10 @@ describe Vote do
   let(:vote) { create(:vote, event: event, user: user) }
 
   describe 'validation' do
+    it { is_expected.to validate_uniqueness_of(:user_id).scoped_to(:event_id) }
+
     it 'has a valid factory' do
       expect(build(:vote)).to be_valid
     end
-
-    it 'validates uniqueness of event in scope of user' do
-      expect(build(:vote, event: vote.event, user: vote.user)).not_to be_valid
-    end
   end
 end