Currency update fix (#4303)

* Call function rather than just looking at it

* Simple unit test POSTs to currency refresh endpoint

* Check if rates have been updated

InvenTree/common/api.py

@@ -154,7 +154,7 @@ class CurrencyRefreshView(APIView):
 
         from InvenTree.tasks import update_exchange_rates
 
-        update_exchange_rates
+        update_exchange_rates()
 
         return Response({
             'success': 'Exchange rates updated',

InvenTree/common/tests.py

@@ -912,3 +912,16 @@ class CurrencyAPITests(InvenTreeAPITestCase):
 
         self.assertIn('base_currency', response.data)
         self.assertIn('exchange_rates', response.data)
+
+    def test_refresh_endpoint(self):
+        """Call the 'refresh currencies' endpoint"""
+
+        from djmoney.contrib.exchange.models import Rate
+
+        # Delete any existing exchange rate data
+        Rate.objects.all().delete()
+
+        self.post(reverse('api-currency-refresh'))
+
+        # There should be some new exchange rate objects now
+        self.assertTrue(Rate.objects.all().exists())