Add unit test for deleting part which has pricing information (#3986)

* Add unit test for deleting part which has pricing information

* Test delete of part without pricing

* Deal with post_delete errors

1. Deleting a Part deleted related objects (e.g. InternalPriceBreak)
2. post_delete signal is called for InternalPriceBreak
3. Subsequent updates to Part / PartPricing throw error

* Add unit test for deleting a Part via the API

- Add InternalPriceBreak so the previous error condition is checked

* Fix for unit test

* More unit test fixes

(cherry picked from commit fa346257f5)

* Ensure unique part names for unit testing

* Further unit test fixes

InvenTree/part/test_pricing.py

@@ -328,3 +328,44 @@ class PartPricingTests(InvenTreeTestCase):
 
         self.assertEqual(pricing.purchase_cost_min, Money('1.333333', 'USD'))
         self.assertEqual(pricing.purchase_cost_max, Money('1.764706', 'USD'))
+
+    def test_delete_with_pricing(self):
+        """Test for deleting a part which has pricing information"""
+
+        # Create some pricing data
+        self.create_price_breaks()
+
+        # Check that pricing does exist
+        pricing = self.part.pricing
+
+        pricing.update_pricing()
+        pricing.save()
+
+        self.assertIsNotNone(pricing.overall_min)
+        self.assertIsNotNone(pricing.overall_max)
+
+        self.part.active = False
+        self.part.save()
+
+        # Remove the part from the database
+        self.part.delete()
+
+        # Check that the pricing was removed also
+        with self.assertRaises(part.models.PartPricing.DoesNotExist):
+            pricing.refresh_from_db()
+
+    def test_delete_without_pricing(self):
+        """Test that we can delete a part which does not have pricing information"""
+
+        pricing = self.part.pricing
+
+        self.assertIsNone(pricing.pk)
+
+        self.part.active = False
+        self.part.save()
+
+        self.part.delete()
+
+        # Check that part was actually deleted
+        with self.assertRaises(part.models.Part.DoesNotExist):
+            self.part.refresh_from_db()