FIX: ensures thread is cleared when closing it (#21264)

plugins/chat/spec/system/page_objects/chat/chat_side_panel.rb

@@ -6,6 +6,10 @@ module PageObjects
       def has_open_thread?(thread)
         has_css?(".chat-side-panel .chat-thread[data-id='#{thread.id}']")
       end
+
+      def has_no_open_thread?
+        !has_css?(".chat-side-panel .chat-thread")
+      end
     end
   end
 end

plugins/chat/spec/system/page_objects/chat/chat_thread.rb

@@ -11,6 +11,10 @@ module PageObjects
         header.find(".chat-thread__omu")
       end
 
+      def close
+        header.find(".chat-thread__close").click
+      end
+
       def has_header_content?(content)
         header.has_content?(content)
       end