test(tcp): add coverage for remote_has_sack in SYN-SENT state

Author: XOR-op

src/socket/tcp.rs

@@ -3725,6 +3725,63 @@ mod test {
         assert_eq!(s.state, State::Closed);
     }
 
+    #[test]
+    fn test_syn_sent_sack_option() {
+        let mut s = socket_syn_sent();
+        recv!(
+            s,
+            [TcpRepr {
+                control: TcpControl::Syn,
+                seq_number: LOCAL_SEQ,
+                ack_number: None,
+                max_seg_size: Some(BASE_MSS),
+                window_scale: Some(0),
+                sack_permitted: true,
+                ..RECV_TEMPL
+            }]
+        );
+        send!(
+            s,
+            TcpRepr {
+                control: TcpControl::Syn,
+                seq_number: REMOTE_SEQ,
+                ack_number: Some(LOCAL_SEQ + 1),
+                max_seg_size: Some(BASE_MSS - 80),
+                window_scale: Some(0),
+                sack_permitted: true,
+                ..SEND_TEMPL
+            }
+        );
+        assert!(s.remote_has_sack);
+
+        let mut s = socket_syn_sent();
+        recv!(
+            s,
+            [TcpRepr {
+                control: TcpControl::Syn,
+                seq_number: LOCAL_SEQ,
+                ack_number: None,
+                max_seg_size: Some(BASE_MSS),
+                window_scale: Some(0),
+                sack_permitted: true,
+                ..RECV_TEMPL
+            }]
+        );
+        send!(
+            s,
+            TcpRepr {
+                control: TcpControl::Syn,
+                seq_number: REMOTE_SEQ,
+                ack_number: Some(LOCAL_SEQ + 1),
+                max_seg_size: Some(BASE_MSS - 80),
+                window_scale: Some(0),
+                sack_permitted: false,
+                ..SEND_TEMPL
+            }
+        );
+        assert!(!s.remote_has_sack);
+    }
+
     #[test]
     fn test_syn_sent_win_scale_buffers() {
         for (buffer_size, shift_amt) in &[