chore: add tests for keep connection feature (#27)

* fix: move `db_path` & `_connection` setup ahead of any fallible ops

`db_path` and `_connection` are now initialized before running code that
could raise, ensuring `__del__` never touches undefined attributes even
if later steps fail.

Author: ktanaka101

src/mcp_server_duckdb/server.py

@@ -17,6 +17,8 @@
 class DuckDBDatabase:
     def __init__(self, config: Config):
         self.config = config
+        self.db_path = config.db_path
+        self._connection = None
 
         dir_path = config.db_path.parent
         if not dir_path.exists():
@@ -33,9 +35,6 @@ def __init__(self, config: Config):
             logger.info(f"Creating DuckDB database: {config.db_path}")
             duckdb.connect(config.db_path).close()
 
-        self.db_path = config.db_path
-        self._connection = None
-
     def connect(self):
         if self.config.keep_connection:
             if self._connection is None:

tests/test_server.py

@@ -137,3 +137,22 @@ def test_readonly_flag_behavior():
 
         result = db_ro.execute_query("SHOW TABLES;")
         assert result == [("ro_test",)]
+
+
+def test_temp_table_persists_with_keep_connection():
+    with tempfile.TemporaryDirectory() as tmpdir:
+        cfg = Config(db_path=Path(tmpdir) / "test.db", keep_connection=True, readonly=False)
+        db = DuckDBDatabase(cfg)
+
+        db.execute_query("CREATE TEMP TABLE t AS SELECT 1 AS v")
+        assert db.execute_query("SELECT v FROM t") == [(1,)]
+
+
+def test_temp_table_does_not_persist_without_keep_connection():
+    with tempfile.TemporaryDirectory() as tmpdir:
+        cfg = Config(db_path=Path(tmpdir) / "test.db", keep_connection=False, readonly=False)
+        db = DuckDBDatabase(cfg)
+
+        db.execute_query("CREATE TEMP TABLE t AS SELECT 1 AS v")
+        with pytest.raises(duckdb.Error):
+            db.execute_query("SELECT v FROM t")