          self.assertEquals(serializer.is_valid(), True)
          self.assertEquals(serializer.object, expected)
          self.assertFalse(serializer.object is expected)
  
      def test_update(self):
          serializer = CommentSerializer(self.data, instance=self.comment)
          expected = self.comment
 
</s> remove         serializer = CommentSerializer(instance=self.comment)
        expected = self.data
        self.assertEquals(serializer.data, expected)
 </s> add         serializer = CommentSerializer(instance=self.comment)        
        self.assertEquals(serializer.data, self.expected) </s> remove 
 </s> add     sub_comment = serializers.Field(source='get_sub_comment.sub_comment')
    
        self.assertEquals(serializer.data['sub_comment'], 'And Merry Christmas!')
          self.assertEquals(serializer.is_valid(), True)
          self.assertEquals(serializer.object, expected)
          self.assertFalse(serializer.object is expected)
        self.assertEquals(serializer.data['sub_comment'], 'And Merry Christmas!')
  
      def test_update(self):
          serializer = CommentSerializer(self.data, instance=self.comment)
          expected = self.comment
keep keep add keep keep keep keep
 Added tests for dotted notation in serializer field source 
rest_framework/tests/serializer.py