Initial production analytics foundation

tests/test_domain_models.py

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+from datetime import UTC, datetime, timedelta
+import unittest
+
+from production_analytics.domain import SourceRange
+
+
+class SourceRangeTests(unittest.TestCase):
+    def test_accepts_ordered_timestamps(self) -> None:
+        start = datetime(2026, 1, 1, tzinfo=UTC)
+        source_range = SourceRange(start=start, end=start + timedelta(minutes=1))
+
+        self.assertEqual(source_range.start, start)
+
+
+    def test_rejects_reverse_interval(self) -> None:
+        end = datetime(2026, 1, 1, tzinfo=UTC)
+
+        with self.assertRaisesRegex(ValueError, "must not precede"):
+            SourceRange(start=end + timedelta(seconds=1), end=end)