Add validation for undo_vote_for to avoid a crash

lib/helpers.rb

@@ -63,7 +63,9 @@ helpers do
 
   def undo_vote_for(obj)
     raise ArgumentError, t(:user_id_is_required) unless user
-    user.unvote(obj)
+    if user.voted?(obj)
+      user.unvote(obj)
+    end
     obj.reload.to_hash.to_json
   end
   

spec/api/vote_spec.rb

@@ -49,6 +49,18 @@ describe "app" do
         comment.up_votes_count.should == prev_up_votes - 1
         comment.down_votes_count.should == prev_down_votes
       end
+      it "unvote on the comment is idempotent" do
+        user = User.first
+        comment = Comment.first
+        prev_up_votes = comment.up_votes_count
+        prev_down_votes = comment.down_votes_count
+        delete "/api/v1/comments/#{comment.id}/votes", user_id: user.id
+        # multiple calls to unvote endpoint should not change the data
+        delete "/api/v1/comments/#{comment.id}/votes", user_id: user.id
+        comment = Comment.find(comment.id)
+        comment.up_votes_count.should == prev_up_votes - 1
+        comment.down_votes_count.should == prev_down_votes
+      end
       it "returns 400 when the comment does not exist" do
         delete "/api/v1/comments/does_not_exist/votes", user_id: User.first.id
         last_response.status.should == 400
@@ -71,6 +83,17 @@ describe "app" do
         thread.up_votes_count.should == prev_up_votes - 1
         thread.down_votes_count.should == prev_down_votes + 1
       end
+      it "vote on the thread is idempotent" do
+        user = User.first
+        thread = CommentThread.first
+        prev_up_votes = thread.up_votes_count
+        prev_down_votes = thread.down_votes_count
+        put "/api/v1/threads/#{thread.id}/votes", user_id: user.id, value: "down"
+        put "/api/v1/threads/#{thread.id}/votes", user_id: user.id, value: "down"
+        thread = CommentThread.find(thread.id)
+        thread.up_votes_count.should == prev_up_votes - 1
+        thread.down_votes_count.should == prev_down_votes + 1
+      end
       it "returns 400 when the thread does not exist" do
         put "/api/v1/threads/does_not_exist/votes", user_id: User.first.id, value: "down"
         last_response.status.should == 400