Fix test failing due to race condition in scheduling the heartbeat timer

Author: davidsteiner

crates/hotfix/tests/session_tests.rs

@@ -37,6 +37,7 @@ async fn test_heartbeats() {
         .await;
     // counterparty responds with a logon to establish a happy session
     mock_counterparty.send_logon().await;
+    tokio::time::advance(std::time::Duration::from_millis(5)).await;
 
     // let's wait enough time for a heartbeat and assert that the heartbeat was sent
     tokio::time::advance(std::time::Duration::from_secs(HEARTBEAT_INTERVAL + 1)).await;