Refactor database module and add testing utilities

Simplify database module by re-organizing engine creation, session handling, and removing redundant methods. Introduce SQLite compatibility for testing and add a utility module for test database setup and teardown. Integrate initial unit tests for user models and update dependencies for security and testing.

backend/app/utils/test_utils.py

@@ -0,0 +1,45 @@
+import logging
+from sqlalchemy import create_engine, event
+from sqlalchemy.orm import sessionmaker, clear_mappers
+from sqlalchemy.pool import StaticPool
+
+from app.core.database import Base
+
+logger = logging.getLogger(__name__)
+
+def get_test_engine():
+    """Create an SQLite in-memory engine specifically for testing"""
+    test_engine = create_engine(
+        "sqlite:///:memory:",
+        connect_args={"check_same_thread": False},
+        poolclass=StaticPool,  # Use static pool for in-memory testing
+        echo=False
+    )
+
+    return test_engine
+
+def setup_test_db():
+    """Create a test database and session factory"""
+    # Create a new engine for this test run
+    test_engine = get_test_engine()
+
+    # Create tables
+    Base.metadata.create_all(test_engine)
+
+    # Create session factory
+    TestingSessionLocal = sessionmaker(
+        autocommit=False,
+        autoflush=False,
+        bind=test_engine,
+        expire_on_commit=False
+    )
+
+    return test_engine, TestingSessionLocal
+
+def teardown_test_db(engine):
+    """Clean up after tests"""
+    # Drop all tables
+    Base.metadata.drop_all(engine)
+
+    # Dispose of engine
+    engine.dispose()