          
  class ReadOnlyManyToManyTests(TestCase):
      def setUp(self):
          class ReadOnlyManyToManySerializer(serializers.ModelSerializer):
              rel =  serializers.ManyRelatedField(readonly=True)
              class Meta:
                  model = ReadOnlyManyToManyModel
  
          self.serializer_class = ReadOnlyManyToManySerializer
  
 
</s> remove             kwargs['default'] = model_field.default
 </s> add             kwargs['default'] = model_field.get_default() </s> remove             'title':'Some action item',
 </s> add             'title': 'Some action item',
            rel = serializers.ManyRelatedField(readonly=True)

          
  class ReadOnlyManyToManyTests(TestCase):
      def setUp(self):
          class ReadOnlyManyToManySerializer(serializers.ModelSerializer):
            rel = serializers.ManyRelatedField(readonly=True)

              class Meta:
                  model = ReadOnlyManyToManyModel
  
          self.serializer_class = ReadOnlyManyToManySerializer
  
keep keep keep keep replace keep keep keep keep keep
 Fix failing 'default' on ModelSerializer 
rest_framework/tests/serializer.py