DRIVER-153: tests for ExecuteMessage use_metadata_id flag and sentinel behaviour

- test_execute_message_scylla_metadata_id_v4: require use_metadata_id=True
  to reflect the new API (field is gated on the flag, not on non-None value)
- test_execute_message_scylla_metadata_id_none_writes_sentinel: new test —
  extension active but result_metadata_id=None writes empty sentinel b''
  (\x00\x00 + b'') keeping the frame layout correct for LWT / mixed-cluster
- test_response_future skip_meta tests: assert message.use_metadata_id to
  cover all four cases (extension on/off, metadata id present/absent, LWT,
  protocol v5)

Author: nikagra

tests/unit/test_protocol.py

@@ -83,9 +83,10 @@ def test_execute_message_skip_meta_flag(self):
         self._check_calls(mock_io, [(b'\x00\x01',), (b'1',), (b'\x00\x04',), (b'\x03',), (b'\x00\x00',)])
 
     def test_execute_message_scylla_metadata_id_v4(self):
-        """result_metadata_id should be written on protocol v4 when set (Scylla extension)."""
+        """result_metadata_id should be written on protocol v4 when use_metadata_id=True (Scylla extension)."""
         message = ExecuteMessage('1', [], 4)
         message.result_metadata_id = b'foo'
+        message.use_metadata_id = True
         mock_io = Mock()
 
         message.send_body(mock_io, 4)
@@ -94,6 +95,23 @@ def test_execute_message_scylla_metadata_id_v4(self):
                                     (b'\x00\x03',), (b'foo',),
                                     (b'\x00\x04',), (b'\x01',), (b'\x00\x00',)])
 
+    def test_execute_message_scylla_metadata_id_none_writes_sentinel(self):
+        """
+        When use_metadata_id=True but result_metadata_id is None (e.g. LWT statement or
+        mixed cluster), send_body must still write the field as an empty string sentinel
+        (\\x00\\x00) so the frame layout matches what the server expects.
+        """
+        message = ExecuteMessage('1', [], 4)
+        message.use_metadata_id = True
+        # result_metadata_id intentionally left as None
+        mock_io = Mock()
+
+        message.send_body(mock_io, 4)
+        # empty sentinel: \x00\x00 (zero-length short) + b'' (zero bytes), then normal query params
+        self._check_calls(mock_io, [(b'\x00\x01',), (b'1',),
+                                    (b'\x00\x00',), (b'',),
+                                    (b'\x00\x04',), (b'\x01',), (b'\x00\x00',)])
+
     def test_recv_results_prepared_scylla_extension_reads_metadata_id(self):
         """
         When use_metadata_id is True (Scylla extension), result_metadata_id must be

tests/unit/test_response_future.py

@@ -904,8 +904,7 @@ def test_query_sets_skip_meta_with_scylla_extension(self):
 
         assert rf.message.skip_meta is True
         assert rf.message.result_metadata_id == b'meta_hash'
-
-    def test_query_no_skip_meta_without_extension(self):
+        assert rf.message.use_metadata_id is True
         """
         When the connection does NOT have SCYLLA_USE_METADATA_ID (and protocol
         is v4), _query() must leave skip_meta=False and result_metadata_id=None.
@@ -929,6 +928,7 @@ def test_query_no_skip_meta_without_extension(self):
 
         assert rf.message.skip_meta is False
         assert rf.message.result_metadata_id is None
+        assert rf.message.use_metadata_id is False
 
     def test_query_no_skip_meta_when_prepared_statement_has_no_metadata_id(self):
         """
@@ -955,6 +955,7 @@ def test_query_no_skip_meta_when_prepared_statement_has_no_metadata_id(self):
 
         assert rf.message.skip_meta is False
         assert rf.message.result_metadata_id is None
+        assert rf.message.use_metadata_id is True  # extension active — field must still appear on wire
 
     def test_query_sets_skip_meta_for_protocol_v5(self):
         """
@@ -981,6 +982,7 @@ def test_query_sets_skip_meta_for_protocol_v5(self):
 
         assert rf.message.skip_meta is True
         assert rf.message.result_metadata_id == b'v5_hash'
+        assert rf.message.use_metadata_id is False  # v5 native path; Scylla extension not active
 
     def test_query_no_skip_meta_when_result_metadata_is_none(self):
         """
@@ -1015,3 +1017,4 @@ def test_query_no_skip_meta_when_result_metadata_is_none(self):
 
         assert rf.message.skip_meta is False
         assert rf.message.result_metadata_id is None
+        assert rf.message.use_metadata_id is True  # extension active — sentinel b'' will be written