Replace assert with proper InternalError for protocol checks

assert statements are stripped with python -O. Use explicit if/raise
with InternalError for a clear error message in optimized deployments.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitedbapi/aio/cursor.py

@@ -3,7 +3,7 @@
 from collections.abc import Sequence
 from typing import TYPE_CHECKING, Any
 
-from dqlitedbapi.exceptions import InterfaceError
+from dqlitedbapi.exceptions import InterfaceError, InternalError
 
 if TYPE_CHECKING:
     from dqlitedbapi.aio.connection import AsyncConnection
@@ -89,14 +89,16 @@ async def execute(
         )
 
         if is_query:
-            assert conn._protocol is not None and conn._db_id is not None
+            if conn._protocol is None or conn._db_id is None:
+                raise InternalError("Connection protocol not initialized")
             columns, rows = await conn._protocol.query_sql(conn._db_id, operation, params)
             self._description = [(name, None, None, None, None, None, None) for name in columns]
             self._rows = [tuple(row) for row in rows]
             self._row_index = 0
             self._rowcount = len(rows)
         else:
-            assert conn._protocol is not None and conn._db_id is not None
+            if conn._protocol is None or conn._db_id is None:
+                raise InternalError("Connection protocol not initialized")
             last_id, affected = await conn._protocol.exec_sql(conn._db_id, operation, params)
             self._lastrowid = last_id
             self._rowcount = affected

src/dqlitedbapi/cursor.py

@@ -3,7 +3,7 @@
 from collections.abc import Sequence
 from typing import TYPE_CHECKING, Any
 
-from dqlitedbapi.exceptions import InterfaceError
+from dqlitedbapi.exceptions import InterfaceError, InternalError
 
 if TYPE_CHECKING:
     from dqlitedbapi.connection import Connection
@@ -101,14 +101,16 @@ async def _execute_async(self, operation: str, parameters: Sequence[Any] | None
         )
 
         if is_query:
-            assert conn._protocol is not None and conn._db_id is not None
+            if conn._protocol is None or conn._db_id is None:
+                raise InternalError("Connection protocol not initialized")
             columns, rows = await conn._protocol.query_sql(conn._db_id, operation, params)
             self._description = [(name, None, None, None, None, None, None) for name in columns]
             self._rows = [tuple(row) for row in rows]
             self._row_index = 0
             self._rowcount = len(rows)
         else:
-            assert conn._protocol is not None and conn._db_id is not None
+            if conn._protocol is None or conn._db_id is None:
+                raise InternalError("Connection protocol not initialized")
             last_id, affected = await conn._protocol.exec_sql(conn._db_id, operation, params)
             self._lastrowid = last_id
             self._rowcount = affected

tests/test_cursor_protocol_check.py

@@ -0,0 +1,52 @@
+"""Tests that cursor raises InternalError when protocol is not initialized."""
+
+import asyncio
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+from dqlitedbapi.cursor import Cursor
+from dqlitedbapi.exceptions import InternalError
+
+
+def _make_mock_connection_no_protocol() -> MagicMock:
+    """Create a mock Connection where _protocol is None."""
+    mock_async_conn = AsyncMock()
+    mock_async_conn._protocol = None
+    mock_async_conn._db_id = None
+
+    mock_conn = MagicMock()
+
+    async def get_async_conn() -> AsyncMock:
+        return mock_async_conn
+
+    mock_conn._get_async_connection = get_async_conn
+
+    def run_sync(coro: object) -> object:
+        loop = asyncio.new_event_loop()
+        try:
+            return loop.run_until_complete(coro)
+        finally:
+            loop.close()
+
+    mock_conn._run_sync = run_sync
+
+    return mock_conn
+
+
+class TestCursorProtocolCheck:
+    def test_execute_query_raises_internal_error_when_protocol_none(self) -> None:
+        """execute() should raise InternalError, not AssertionError, when protocol is None."""
+        mock_conn = _make_mock_connection_no_protocol()
+        cursor = Cursor(mock_conn)
+
+        with pytest.raises(InternalError, match="Connection protocol not initialized"):
+            cursor.execute("SELECT 1")
+
+    def test_execute_dml_raises_internal_error_when_protocol_none(self) -> None:
+        """execute() should raise InternalError for DML when protocol is None."""
+        mock_conn = _make_mock_connection_no_protocol()
+        cursor = Cursor(mock_conn)
+
+        with pytest.raises(InternalError, match="Connection protocol not initialized"):
+            cursor.execute("INSERT INTO t VALUES (1)")