chore: resolve 15 low-hanging-fruit tech debt issues

tests/unit/test_db_pool.py

@@ -0,0 +1,80 @@
+"""Tests for the thread-local SQLite ConnectionPool."""
+
+import sqlite3
+import threading
+from pathlib import Path
+
+import pytest
+
+from infrastructure.db_pool import ConnectionPool
+
+pytestmark = pytest.mark.unit
+
+
+def test_pool_creates_connection(tmp_path: Path):
+    """Test that the pool successfully creates a SQLite connection."""
+    db_file = tmp_path / "test.db"
+    pool = ConnectionPool(db_file)
+
+    conn = pool.get_connection()
+    assert isinstance(conn, sqlite3.Connection)
+
+    cursor = conn.execute("SELECT 1")
+    assert cursor.fetchone()[0] == 1
+
+
+def test_pool_reuses_connection_same_thread(tmp_path: Path):
+    """Test that multiple calls in the same thread return the same connection."""
+    db_file = tmp_path / "test.db"
+    pool = ConnectionPool(db_file)
+
+    conn1 = pool.get_connection()
+    conn2 = pool.get_connection()
+    assert conn1 is conn2
+
+
+def test_pool_different_connections_different_threads(tmp_path: Path):
+    """Test that different threads receive distinct connections."""
+    db_file = tmp_path / "test.db"
+    pool = ConnectionPool(db_file)
+
+    conn1 = pool.get_connection()
+    conn2_list = []
+
+    def _worker():
+        conn2_list.append(pool.get_connection())
+
+    thread = threading.Thread(target=_worker)
+    thread.start()
+    thread.join()
+
+    assert len(conn2_list) == 1
+    conn2 = conn2_list[0]
+    assert conn1 is not conn2
+
+
+def test_pool_close_connection(tmp_path: Path):
+    """Test that connection is closed and cleared from thread local."""
+    db_file = tmp_path / "test.db"
+    pool = ConnectionPool(db_file)
+
+    conn1 = pool.get_connection()
+    pool.close_connection()
+
+    # Getting a new connection should create a new object
+    conn2 = pool.get_connection()
+    assert conn1 is not conn2
+
+
+def test_pool_context_manager(tmp_path: Path):
+    """Test that the context manager yields a connection and closes it after."""
+    db_file = tmp_path / "test.db"
+    pool = ConnectionPool(db_file)
+
+    with pool.connection() as conn1:
+        assert isinstance(conn1, sqlite3.Connection)
+
+    # After exiting the context manager, the connection should be closed implicitly
+    # resulting in a new connection object for the next request.
+    conn2 = pool.get_connection()
+    assert conn1 is not conn2