M8-R11: make business timezone deterministic

tests/test_meter_cost_api.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 from datetime import UTC, datetime, timedelta
 from decimal import Decimal
 from unittest.mock import patch
+from zoneinfo import ZoneInfo
 
 import pytest
 from fastapi.testclient import TestClient
@@ -139,7 +140,9 @@ def test_meter_cost_summary_empty_and_recompute_csrf_window_validation(meter_cos
     ).status_code == 422
 
 
-def test_meter_cost_summary_returns_five_fixed_components_and_totals(meter_cost_client) -> None:
+def test_meter_cost_summary_returns_five_fixed_components_and_totals(
+    meter_cost_client, monkeypatch: pytest.MonkeyPatch
+) -> None:
     client, engine = meter_cost_client
     now = datetime.now(UTC)
     values = {
@@ -166,8 +169,10 @@ def test_meter_cost_summary_returns_five_fixed_components_and_totals(meter_cost_
         db.add_all((heating, water))
         db.commit()
     _login(client)
-    with patch("app.api.routes.api.meter_costs.local_now", return_value=datetime(2026, 6, 25, 2, tzinfo=UTC)):
-        response = client.get("/api/energy/meter-costs/summary?scope=thermal&start=2026-06-23T00:00:00Z&end=2026-06-24T00:00:00Z")
+    monkeypatch.setattr("app.services.timezone.local_tz", lambda: ZoneInfo("Europe/Amsterdam"))
+    response = client.get(
+        "/api/energy/meter-costs/summary?scope=thermal&start=2026-06-23T00:00:00Z&end=2026-06-24T00:00:00Z"
+    )
     assert response.status_code == 200
     body = response.json()
     assert body["heating"] == "1.000000000" and body["hot_water_heating"] == "0.8"