Test: block until membership changed for add_learner_with_set_nodes()

tests/tests/membership/t11_add_learner.rs

@@ -181,11 +181,13 @@ async fn add_learner_with_set_nodes() -> Result<()> {
         let raft = router.get_raft_handle(&0)?;
         raft.change_membership(ChangeMembers::SetNodes(btreemap! {2=>(), 4=>()}), true).await?;
 
-        // TODO: Flaky: there is chance that the log is committed but metrics is not updated.
-        //       Because metrics is updated in the next loop in the `runtime_loop`
-        let metrics = router.get_raft_handle(&0)?.metrics().borrow().clone();
-        let node_ids = metrics.membership_config.membership().nodes().map(|x| *x.0).collect::<Vec<_>>();
-        assert_eq!(vec![0, 1, 2, 4], node_ids);
+        router
+            .wait(&0, timeout())
+            .metrics(
+                |m| m.membership_config.membership().nodes().map(|x| *x.0).collect::<Vec<_>>() == vec![0, 1, 2, 4],
+                "set node 2 and 4",
+            )
+            .await?;
     }
 
     Ok(())