Add a test for update notifications

visions/server/src/core.rs

@@ -208,4 +208,23 @@ mod test {
             assert_eq!(background_image, Some(AssetId::from("asset_1")));
         });
     }
+
+    #[tokio::test]
+    async fn it_sends_notices_to_clients_on_tabletop_change() {
+        let core = test_core();
+        let client_id = core.register_client();
+        let mut receiver = core.connect_client(client_id);
+
+        assert_matches!(core.set_background_image(AssetId::from("asset_1")), Ok(()));
+        match receiver.recv().await {
+            Some(Message::UpdateTabletop(Tabletop {
+                background_color,
+                background_image,
+            })) => {
+                assert_eq!(background_color, DEFAULT_BACKGROUND_COLOR);
+                assert_eq!(background_image, Some(AssetId::from("asset_1")));
+            }
+            None => panic!("receiver did not get a message"),
+        }
+    }
 }