test(managed): verify blocking owner lifecycle

crates/irtt-client/src/managed/blocking.rs

@@ -84,14 +84,22 @@ impl BlockingManagedClient {
     }
 
     fn join_worker(&mut self) -> Result<ManagedOutcome, BlockingManagedJoinError> {
-        self.worker
-            .take()
-            .expect("blocking managed worker is joined at most once")
-            .join()
-            .map_err(|_| BlockingManagedJoinError::WorkerPanicked)
+        join_worker(
+            self.worker
+                .take()
+                .expect("blocking managed worker is joined at most once"),
+        )
     }
 }
 
+pub(super) fn join_worker(
+    worker: JoinHandle<ManagedOutcome>,
+) -> Result<ManagedOutcome, BlockingManagedJoinError> {
+    worker
+        .join()
+        .map_err(|_| BlockingManagedJoinError::WorkerPanicked)
+}
+
 impl Drop for BlockingManagedClient {
     fn drop(&mut self) {
         if self.worker.is_some() {