test: upgrade backend test suite, implement unit tests, and modernize CRUD patterns

backend/tests/test_database.py

@@ -0,0 +1,29 @@
+import pytest
+from unittest.mock import patch
+from sqlalchemy.ext.asyncio import create_async_engine
+from sqlalchemy import text
+from sqlmodel import SQLModel
+from app.database import init_db
+
+@pytest.mark.asyncio
+async def test_init_db_creates_tables():
+    """Verifies that init_db() successfully creates all necessary tables.
+
+    This test uses a patched in-memory SQLite engine to ensure isolation
+    and verify the database initialization logic.
+    """
+    # Use an in-memory SQLite engine for testing to avoid any impact on real data
+    test_engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    
+    # Patch the engine in app.database so init_db uses our test engine
+    with patch("app.database.engine", test_engine):
+        await init_db()
+        
+        # Check if the expected table "sleep_session" exists in the schema
+        async with test_engine.connect() as conn:
+            result = await conn.execute(text("SELECT name FROM sqlite_master WHERE type='table' AND name='sleep_session';"))
+            row = result.fetchone()
+            assert row is not None, "Table 'sleep_session' was not created by init_db()"
+            assert row[0] == "sleep_session"
+
+    await test_engine.dispose()