grandpa: fix slow gossip test (#4440)

substrate/client/finality-grandpa/src/communication/tests.rs

@@ -274,16 +274,25 @@ fn good_commit_leads_to_relay() {
 			let sender_id = id.clone();
 			let send_message = tester.filter_network_events(move |event| match event {
 				Event::EventStream(sender) => {
+					// Add the sending peer and send the commit
 					let _ = sender.unbounded_send(NetworkEvent::NotificationStreamOpened {
 						remote: sender_id.clone(),
 						engine_id: GRANDPA_ENGINE_ID,
 						roles: Roles::FULL,
 					});
+
 					let _ = sender.unbounded_send(NetworkEvent::NotificationsReceived {
 						remote: sender_id.clone(),
 						messages: vec![(GRANDPA_ENGINE_ID, commit_to_send.clone().into())],
 					});
 
+					// Add a random peer which will be the recipient of this message
+					let _ = sender.unbounded_send(NetworkEvent::NotificationStreamOpened {
+						remote: sc_network::PeerId::random(),
+						engine_id: GRANDPA_ENGINE_ID,
+						roles: Roles::FULL,
+					});
+
 					true
 				}
 				_ => false,