Add interaction tests (#15251)

Content.Server/Construction/ConstructionSystem.Graph.cs

@@ -352,6 +352,10 @@ namespace Content.Server.Construction
                 }
             }
 
+            var entChangeEv = new ConstructionChangeEntityEvent(newUid, uid);
+            RaiseLocalEvent(uid, entChangeEv);
+            RaiseLocalEvent(newUid, entChangeEv, broadcast: true);
+
             QueueDel(uid);
 
             return newUid;
@@ -384,4 +388,20 @@ namespace Content.Server.Construction
             return ChangeNode(uid, userUid, nodeId, performActions, construction);
         }
     }
+
+    /// <summary>
+    ///     This event gets raised when an entity changes prototype / uid during construction. The event is raised
+    ///     directed both at the old and new entity.
+    /// </summary>
+    public sealed class ConstructionChangeEntityEvent : EntityEventArgs
+    {
+        public readonly EntityUid New;
+        public readonly EntityUid Old;
+
+        public ConstructionChangeEntityEvent(EntityUid newUid, EntityUid oldUid)
+        {
+            New = newUid;
+            Old = oldUid;
+        }
+    }
 }