          serializer.save()
  
          # Ensure source 1 is updated, and everything else is as expected
          queryset = ManyToManySource.objects.all()
          serializer = ManyToManySourceSerializer(instance=queryset)
          expected = [
                  {'id': 1, 'name': u'source-1', 'targets': [1, 2, 3]},
                  {'id': 2, 'name': u'source-2', 'targets': [1, 2]},
                  {'id': 3, 'name': u'source-3', 'targets': [1, 2, 3]}
          ]
 
</s> remove         serializer = self.serializer_class(data)
 </s> add         serializer = self.serializer_class(data=data) </s> remove         serializer = self.not_blank_model_serializer_class(self.data)
 </s> add         serializer = self.not_blank_model_serializer_class(data=self.data) </s> remove         serializer = CommentSerializer(self.data, instance=self.comment)
 </s> add         serializer = CommentSerializer(self.comment, data=self.data)
        serializer = ManyToManySourceSerializer(queryset)
          serializer.save()
  
          # Ensure source 1 is updated, and everything else is as expected
          queryset = ManyToManySource.objects.all()
        serializer = ManyToManySourceSerializer(queryset)
          expected = [
                  {'id': 1, 'name': u'source-1', 'targets': [1, 2, 3]},
                  {'id': 2, 'name': u'source-2', 'targets': [1, 2]},
                  {'id': 3, 'name': u'source-3', 'targets': [1, 2, 3]}
          ]
keep keep keep keep replace keep keep keep keep keep
 Swap position of `instance` and `data` keyword arguments. 
rest_framework/tests/pk_relations.py