Fix: recv returns an Option<Ticket>

exercises/07_threads/07_ack/tests/insert.rs

@@ -34,7 +34,10 @@ fn insert_works() {
         .send(command)
         .expect("Did you actually spawn a thread? The channel is closed!");
 
-    let ticket: Ticket = response_receiver.recv().expect("No response received!");
+    let ticket: Ticket = response_receiver
+        .recv()
+        .expect("No response received!")
+        .unwrap();
     assert_eq!(ticket_id, ticket.id);
     assert_eq!(ticket.status, Status::ToDo);
     assert_eq!(ticket.title, draft.title);