Add sensor freshness checks

tests/test_data_quality.py

@@ -0,0 +1,40 @@
+"""Timestamp boundaries and UI translation coverage without HA dependencies."""
+import importlib.util
+import json
+import unittest
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parents[1] / 'custom_components' / 'heating_mpc'
+spec = importlib.util.spec_from_file_location('quality', ROOT / 'data_quality.py')
+quality = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(quality)
+
+
+class FreshnessTests(unittest.TestCase):
+    def test_age_boundaries(self):
+        now = datetime(2026, 10, 26, tzinfo=timezone.utc)
+        for seconds, expected in ((0, 'valid'), (1800, 'valid'), (1801, 'stale'), (-1, 'future_timestamp')):
+            with self.subTest(seconds=seconds):
+                result = quality.freshness(now - timedelta(seconds=seconds), now, 1800)
+                self.assertEqual(result['status'], expected)
+                self.assertEqual(result['age_seconds'], seconds)
+
+    def test_missing_naive_and_malformed_times(self):
+        now = datetime.now(timezone.utc)
+        for timestamp in (None, 'bad', datetime.now()):
+            self.assertEqual(quality.freshness(timestamp, now, 1800)['status'], 'invalid_timestamp')
+
+    def test_invalid_limits_rejected(self):
+        now = datetime.now(timezone.utc)
+        for limit in (0, -1, float('inf'), float('nan')):
+            with self.assertRaises(ValueError):
+                quality.freshness(now, now, limit)
+
+    def test_freshness_settings_translated(self):
+        for name in ('strings.json', 'translations/en.json', 'translations/ro.json'):
+            data = json.loads((ROOT / name).read_text())
+            for section, step in (('config', 'user'), ('options', 'init')):
+                labels = data[section]['step'][step]['data']
+                for key in ('room_max_age_minutes', 'weather_max_age_minutes'):
+                    self.assertTrue(labels[key])