title: AttributeError: This QueryDict instance is immutable for test cases
body: <p>I am trying to change my request.data dict to remove some additional field.
  It is working completely fine in views.
  But when I run test cases for the same, I get this error:</p>
  
  <p>AttributeError: This QueryDict instance is immutable</p>
  
  <p>Here is my viewset:</p>
  
  <pre><code>    def create(self, request, *args, **kwargs):
  
          context = {'view': self, 'request': request}
  
          addresses = request.data.pop("addresses", None)
          serializer = self.get_serializer(data=request.data, context=context)
          serializer.is_valid(raise_exception=True)
          response = super(WarehouseViewSet, self).create(request, *args, **kwargs)
          if addresses is None:
              pass
          else:
              serializer = self.get_serializer(data=request.data, context=context)
              serializer.is_valid(raise_exception=True)
              addresses = serializer.update_warehouse_address(request, addresses, response.data["id"])
              response.data["addresses"] = addresses
          return Response(data=response.data, status=status.HTTP_201_CREATED)
  </code></pre>
  
  <p>and here is my test case for the same view:</p>
  
  <pre><code>    def test_create_warehouse_authenticated(self):
          response = client.post(
              reverse('warehouse_list_create'),
              data={
                  'name': self.test_warehouse['test_warehouse']['name'],
                  'branch': self.test_warehouse['test_warehouse']['branch'],
              },
              **{'HTTP_AUTHORIZATION': 'Bearer {}'.format(
                  self.test_users['test_user']['access_token']
              )},
          )
  
          self.assertEqual(response.status_code, status.HTTP_201_CREATED)
  </code></pre>
  
  <p>How to fix this error?</p>