adds extra specs for debate's cache

spec/models/debate_spec.rb

@@ -286,6 +286,16 @@ describe Debate do
       .to change { debate.updated_at }
     end
 
+    it "should expire cache when hidden" do
+      expect { debate.hide }
+      .to change { debate.updated_at }
+    end
+
+    it "should expire cache when the author is hidden" do
+      expect { debate.author.hide }
+      .to change { [debate.reload.updated_at, debate.author.updated_at] }
+    end
+
     it "should expire cache when its author changes" do
       expect { debate.author.update(username: "Eva") }
       .to change { [debate.reload.updated_at, debate.author.updated_at] }