Document rules and enforce price value uniqueness

modules/purchase_trade/tests/test_module.py

@@ -6,7 +6,9 @@ from datetime import date
 from types import SimpleNamespace
 from unittest.mock import Mock, patch
 
+from trytond.model.exceptions import ValidationError
 from trytond.pool import Pool
+from trytond.modules.price.price_value import PriceValue
 from trytond.tests.test_tryton import ModuleTestCase, with_transaction
 from trytond.modules.purchase_trade.pricing import ImportPrices
 
@@ -306,6 +308,37 @@ class PurchaseTradeTestCase(ModuleTestCase):
         self.assertIn('Errors:', message)
         self.assertIn('Row 2 - LME Copper / 2026-03-27', message)
 
+    def test_price_value_unique_rejects_duplicate_create(self):
+        'price value uniqueness rejects duplicate model creation'
+        price_value = SimpleNamespace(
+            id=None,
+            price=SimpleNamespace(id=1),
+            price_date=date(2026, 3, 27),
+            )
+
+        with patch.object(
+                PriceValue, 'search',
+                return_value=[SimpleNamespace(id=2)]):
+            with self.assertRaises(ValidationError):
+                PriceValue.check_unique_price_date([price_value])
+
+    def test_price_value_unique_rejects_duplicate_write(self):
+        'price value uniqueness excludes current record on write'
+        price_value = SimpleNamespace(
+            id=2,
+            price=SimpleNamespace(id=1),
+            price_date=date(2026, 3, 27),
+            )
+
+        with patch.object(
+                PriceValue, 'search',
+                return_value=[SimpleNamespace(id=3)]) as search:
+            with self.assertRaises(ValidationError):
+                PriceValue.check_unique_price_date([price_value])
+
+        domain = search.call_args[0][0]
+        self.assertIn(('id', '!=', 2), domain[1])
+
 
 class _FakePriceModel: