test: move assert to internal function

Author: LeoPatOZ

src/robust_provider/subscription.rs

@@ -388,6 +388,8 @@ mod tests {
         sleep(SHORT_TIMEOUT + extra_delay + BUFFER_TIME).await;
         let err = stream.next().await.unwrap().unwrap_err();
         assert_backend_gone_or_timeout(err);
+        let next = stream.next().await;
+        assert!(next.is_none(), "Expected stream to be finished, got: {next:?}");
     }
 
     #[tokio::test]
@@ -419,9 +421,6 @@ mod tests {
         // Verify: HTTP fallback can't provide subscription, so we get an error
         assert_timeout_error(&mut stream, Duration::ZERO).await;
 
-        let next = stream.next().await;
-        assert!(next.is_none(), "Expected stream to be finished, got: {next:?}");
-
         Ok(())
     }