refactor: update test fixtures for improved database session management and isolation

tests/conftest.py

@@ -6,6 +6,7 @@ import pytest
 from httpx import ASGITransport, AsyncClient
 from sqlalchemy import text
 from sqlalchemy.exc import ProgrammingError
+from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import engine, test_engine, get_test_db, get_db
 from app.main import app
@@ -64,16 +65,43 @@ async def start_db():
     await test_engine.dispose()
 
 
-@pytest.fixture(scope="session")
-async def client(start_db) -> AsyncGenerator[AsyncClient, Any]:  # noqa: ARG001
-    transport = ASGITransport(
-        app=app,
-    )
+@pytest.fixture(scope="function")
+async def db_session(start_db) -> AsyncGenerator[AsyncSession, Any]:
+    """
+    Provide a transactional database session for each test function.
+    Rolls back changes after the test.
+    """
+    connection = await test_engine.connect()
+    transaction = await connection.begin()
+    session = AsyncSession(bind=connection)
+
+    yield session
+
+    await session.close()
+    await transaction.rollback()
+    await connection.close()
+
+
+@pytest.fixture(scope="function")
+async def client(db_session: AsyncSession) -> AsyncGenerator[AsyncClient, Any]:
+    """
+    Provide a test client for making API requests.
+    Uses the function-scoped db_session for test isolation.
+    """
+
+    def get_test_db_override():
+        yield db_session
+
+    app.dependency_overrides[get_db] = get_test_db_override
+    app.redis = await get_redis()
+
+    transport = ASGITransport(app=app)
     async with AsyncClient(
         base_url="http://testserver/v1",
         headers={"Content-Type": "application/json"},
         transport=transport,
     ) as test_client:
-        app.dependency_overrides[get_db] = get_test_db
-        app.redis = await get_redis()
         yield test_client
+
+    # Clean up dependency overrides
+    del app.dependency_overrides[get_db]