Get a basic first test working, and lots of changes to supporting code to facilitate this

backend/telemetry_core/src/feed_message.rs

@@ -231,4 +231,4 @@ impl FeedMessageWrite for AddedNode<'_> {
             &node.startup_time(),
         ));
     }
-}
+}

backend/telemetry_core/src/main.rs

@@ -308,17 +308,3 @@ where
     // loop ended; give socket back to parent:
     (tx_to_aggregator, websocket)
 }
-
-#[cfg(test)]
-pub mod test {
-
-    use test_utils::test_simple;
-
-    #[test]
-    fn test_feed_connection () {
-
-
-
-    }
-
-}