check uds_stream it is no longer readable

tokio/tests/uds_stream.rs

@@ -317,6 +317,9 @@ async fn try_read_buf() -> std::io::Result<()> {
         }
 
         assert_eq!(read, written);
+
+        let mut readable = task::spawn(server.readable());
+        assert_pending!(readable.poll());
     }
 
     // Now, we listen for shutdown