diff --git a/federate/federate-core/src/lib.rs b/federate/federate-core/src/lib.rs
index 3df5619..e7c9443 100644
--- a/federate/federate-core/src/lib.rs
+++ b/federate/federate-core/src/lib.rs
@@ -76,6 +76,9 @@ pub trait Federate: Sync + Send {
 
     /// publish results in tar ball
     async fn tar(&self) -> Result<PathBuf, Self::Error>;
+
+    /// get latest tar ball
+    async fn latest_tar(&self) -> Result<PathBuf, Self::Error>;
 }
 
 pub fn get_hostname(url: &Url) -> &str {
diff --git a/federate/federate-core/src/tests.rs b/federate/federate-core/src/tests.rs
index 5a2fc80..fed217b 100644
--- a/federate/federate-core/src/tests.rs
+++ b/federate/federate-core/src/tests.rs
@@ -53,7 +53,9 @@ pub async fn adding_forge_works<'a, T: Federate>(
         .unwrap());
 
     // tar()
-    ff.tar().await.unwrap();
+    let tar = ff.tar().await.unwrap();
+    let latest = ff.latest_tar().await.unwrap();
+    assert_eq!(tar, latest);
 
     // delete repository
     ff.delete_repository(add_repo_msg.owner, add_repo_msg.name, &add_repo_msg.url)