Feature: add Wait::purged() to wait for purged to become the expected

openraft/src/metrics/wait.rs

@@ -5,6 +5,7 @@ use tokio::sync::watch;
 use tokio::time::Instant;
 
 use crate::core::ServerState;
+use crate::display_ext::DisplayOption;
 use crate::metrics::RaftMetrics;
 use crate::node::Node;
 use crate::LogId;
@@ -190,4 +191,14 @@ where
         )
         .await
     }
+
+    /// Wait for `purged` to become `want` or timeout.
+    #[tracing::instrument(level = "trace", skip(self), fields(msg=msg.to_string().as_str()))]
+    pub async fn purged(&self, want: Option<LogId<NID>>, msg: impl ToString) -> Result<RaftMetrics<NID, N>, WaitError> {
+        self.metrics(
+            |x| x.purged == want,
+            &format!("{} .purged -> {}", msg.to_string(), DisplayOption(&want)),
+        )
+        .await
+    }
 }

openraft/src/metrics/wait_test.rs

@@ -10,6 +10,7 @@ use crate::core::ServerState;
 use crate::log_id::LogIdOptionExt;
 use crate::metrics::Wait;
 use crate::metrics::WaitError;
+use crate::testing::log_id;
 use crate::vote::CommittedLeaderId;
 use crate::LogId;
 use crate::Membership;
@@ -170,6 +171,24 @@ async fn test_wait() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 8)]
+async fn test_wait_purged() -> anyhow::Result<()> {
+    let (init, w, tx) = init_wait_test::<u64, ()>();
+
+    let h = tokio::spawn(async move {
+        sleep(Duration::from_millis(10)).await;
+        let mut update = init.clone();
+        update.purged = Some(log_id(1, 2, 3));
+        let rst = tx.send(update);
+        assert!(rst.is_ok());
+    });
+    let got = w.purged(Some(log_id(1, 2, 3)), "purged").await?;
+    h.await?;
+    assert_eq!(Some(log_id(1, 2, 3)), got.purged);
+
+    Ok(())
+}
+
 pub(crate) type InitResult<NID, N> = (RaftMetrics<NID, N>, Wait<NID, N>, watch::Sender<RaftMetrics<NID, N>>);
 
 /// Build a initial state for testing of Wait: