Stock: More unit tests

- Add some more tests (would have caught a bug that was there already, darn it)

InvenTree/stock/test_api.py

@@ -81,6 +81,59 @@ class StockItemTest(StockAPITestCase):
         response = self.client.get(self.list_url, format='json')
         self.assertEqual(response.status_code, status.HTTP_200_OK)
 
+    def test_stock_item_create(self):
+        """
+        Test creation of a StockItem via the API
+        """
+
+        # POST with an empty part reference
+
+        response = self.client.post(
+            self.list_url,
+            data={
+                'quantity': 10,
+                'location': 1
+            }
+        )
+
+        self.assertContains(response, 'This field is required', status_code=status.HTTP_400_BAD_REQUEST)
+        
+        # POST with an invalid part reference
+
+        response = self.client.post(
+            self.list_url,
+            data={
+                'quantity': 10,
+                'location': 1,
+                'part': 10000000,
+            }
+        )
+
+        self.assertContains(response, 'does not exist', status_code=status.HTTP_400_BAD_REQUEST)
+
+        # POST without quantity
+        response = self.client.post(
+            self.list_url,
+            data={
+                'part': 1,
+                'location': 1,
+            }
+        )
+
+        self.assertContains(response, 'This field is required', status_code=status.HTTP_400_BAD_REQUEST)
+
+        # POST with quantity and part and location
+        response = self.client.post(
+            self.list_url,
+            data={
+                'part': 1,
+                'location': 1,
+                'quantity': 10,
+            }
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_201_CREATED)
+
 
 class StocktakeTest(StockAPITestCase):
     """