Go to one of your collections listed on Special:Gather that is not your watchlist and click edit.
Inside the edit screen go to edit the description (cog icon)
Type text in title/description
Click the back icon in the top left
Actual: You lose the changes - clicking the cog again the things you inputted are lost
Expected: it should warn you about losing save changes using a confirm prompt. When the user says no they are returned to the editor screen
Note: this is a good opportunity to generalise the code in EditOverlay and TalkOverlay