test: enhance admin API tests with database session mocking

- Introduced a mock database session for admin API tests to prevent real database access during CI.
- Updated test cases for the `/api/admin/me` endpoint to ensure consistent behavior without a real database.
- Improved error handling and clarity in tests by utilizing dependency overrides for session management.
- Ensured proper cleanup of dependency overrides after tests to maintain test isolation.

tests/test_admin_api.py

@@ -4,8 +4,10 @@ from unittest.mock import ANY, MagicMock, patch
 
 import pytest
 from fastapi.testclient import TestClient
+from sqlalchemy.orm import Session
 
 from duty_teller.api.app import app
+from duty_teller.api.dependencies import get_db_session
 
 
 @pytest.fixture
@@ -13,15 +15,31 @@ def client():
     return TestClient(app)
 
 
+def _override_get_db_session(mock_session: MagicMock):
+    """Dependency override that returns mock_session (no real DB). Used as get_db_session override."""
+
+    def _override() -> Session:
+        return mock_session
+
+    return _override
+
+
 # --- GET /api/admin/me ---
 
 
 @patch("duty_teller.api.dependencies.config.MINI_APP_SKIP_AUTH", True)
 def test_admin_me_skip_auth_returns_is_admin_false(client):
     """With MINI_APP_SKIP_AUTH, GET /api/admin/me returns is_admin: false (no real user)."""
+    # Override get_db_session so the endpoint does not open the real DB (CI has no data/ dir).
+    mock_session = MagicMock()
+    mock_session.query.return_value.filter.return_value.first.return_value = None
+    app.dependency_overrides[get_db_session] = _override_get_db_session(mock_session)
+    try:
         r = client.get("/api/admin/me")
         assert r.status_code == 200
         assert r.json() == {"is_admin": False}
+    finally:
+        app.dependency_overrides.pop(get_db_session, None)
 
 
 @patch("duty_teller.api.app.is_admin_for_telegram_user")
@@ -245,9 +263,8 @@ def test_admin_reassign_400_when_user_not_found(
     )
     mock_session = MagicMock()
     mock_session.get.return_value = None  # User not found
-    with patch("duty_teller.api.app.get_db_session") as mock_db:
-        mock_db.return_value.__enter__.return_value = mock_session
-        mock_db.return_value.__exit__.return_value = None
+    app.dependency_overrides[get_db_session] = _override_get_db_session(mock_session)
+    try:
         r = client.patch(
             "/api/admin/duties/1",
             json={"user_id": 999},
@@ -255,6 +272,8 @@ def test_admin_reassign_400_when_user_not_found(
                 "X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x"
             },
         )
+    finally:
+        app.dependency_overrides.pop(get_db_session, None)
     assert r.status_code == 400
     mock_update.assert_not_called()
     mock_invalidate.assert_not_called()
@@ -301,9 +320,8 @@ def test_admin_reassign_200_updates_and_invalidates(
     mock_update_duty_user.return_value = updated_duty
     mock_session = MagicMock()
     mock_session.get.return_value = SimpleNamespace(id=2)  # User exists
-    with patch("duty_teller.api.app.get_db_session") as mock_db:
-        mock_db.return_value.__enter__.return_value = mock_session
-        mock_db.return_value.__exit__.return_value = None
+    app.dependency_overrides[get_db_session] = _override_get_db_session(mock_session)
+    try:
         r = client.patch(
             "/api/admin/duties/1",
             json={"user_id": 2},
@@ -311,6 +329,8 @@ def test_admin_reassign_200_updates_and_invalidates(
                 "X-Telegram-Init-Data": "auth_date=1&user=%7B%22id%22%3A1%7D&hash=x"
             },
         )
+    finally:
+        app.dependency_overrides.pop(get_db_session, None)
     assert r.status_code == 200
     data = r.json()
     assert data["id"] == 1