test(base): Ensure viewsets are caching and using the serializer_class object

ref: #513 #518

app/api/tests/abstract/viewsets.py

@@ -660,3 +660,77 @@ class ViewSetModel(
         assert setter_not_called
         assert qs.call_count == 2
 
+
+
+    def test_view_func_get_serializer_class_cache_result(self):
+        """Viewset Test
+
+        Ensure that the `get_serializer_class` function caches the result under
+        attribute `<viewset>.serializer_class`
+        """
+
+        view_set = self.viewset()
+
+        view_set.kwargs = self.kwargs
+
+        view_set.action = 'list'
+
+        view_set.detail = False
+
+        assert view_set.serializer_class is None    # Must be empty before init
+
+        q = view_set.get_serializer_class()
+
+        assert view_set.serializer_class is not None    # Must not be empty after init
+
+        assert q == view_set.serializer_class
+
+
+    def test_view_func_get_serializer_class_cache_result_used(self):
+        """Viewset Test
+
+        Ensure that the `get_serializer_class` function caches the result under
+        attribute `<viewset>.serializer_class`
+        """
+
+        view_set = self.viewset()
+
+        view_set.kwargs = self.kwargs
+        view_set.action = 'list'
+        view_set.detail = False
+
+        mock_return = view_set.get_serializer_class()    # Real item to be used as mock return Some 
+                                                         # functions use `Queryset` for additional filtering
+
+        def bool_rtn(self):
+            return True
+
+        mock_return.__class__.__bool__ = bool_rtn    # Required for truthy if statments to work. i.e. `if self.queryset`
+
+        setter_not_called = True
+
+
+        with patch.object(self.viewset, 'serializer_class', new_callable=PropertyMock) as qs:
+
+            qs.return_value = mock_return
+
+            mocked_view_set = self.viewset()
+
+            mocked_view_set.kwargs = self.kwargs
+            mocked_view_set.action = 'list'
+            mocked_view_set.detail = False
+
+            qs.reset_mock()    # Just in case
+
+            mocked_setup = mocked_view_set.get_serializer_class()    # should only add two calls, if exists and the return
+
+
+            for mock_call in list(qs.mock_calls):    # mock_calls with args means setter was called
+
+                if len(mock_call.args) > 0:
+
+                    setter_not_called = False
+
+
+        assert setter_not_called
+        assert qs.call_count == 2