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/company/models.py

@@ -704,7 +704,7 @@ def after_save_supplier_price(sender, instance, created, **kwargs):
     if InvenTree.ready.canAppAccessDatabase() and not InvenTree.ready.isImportingData():
 
         if instance.part and instance.part.part:
-            instance.part.part.pricing.schedule_for_update()
+            instance.part.part.schedule_pricing_update()
 
 
 @receiver(post_delete, sender=SupplierPriceBreak, dispatch_uid='post_delete_supplier_price_break')
@@ -714,4 +714,4 @@ def after_delete_supplier_price(sender, instance, **kwargs):
     if InvenTree.ready.canAppAccessDatabase() and not InvenTree.ready.isImportingData():
 
         if instance.part and instance.part.part:
-            instance.part.part.pricing.schedule_for_update()
+            instance.part.part.schedule_pricing_update()