A test for 0 item adds().

taggit/managers.py

@@ -132,6 +132,8 @@ class _TaggableManager(models.Manager):
             if not isinstance(t, self.through.tag_model())
         ])
         tag_objs = set(tags) - str_tags
+        # If str_tags has 0 elements Django actually optimizes that to not do a
+        # query.  Malcolm is very smart.
         existing = self.through.tag_model().objects.filter(
             name__in=str_tags
         )

taggit/tests/tests.py

@@ -125,6 +125,8 @@ class TaggableManagerTestCase(BaseTaggingTestCase):
         # + 4 queries to create the intermeidary things (including SELECTs, to
         #   make sure we dont't double create.
         self.assert_num_queries(5, pear.tags.add, "green", "delicious")
+        
+        self.assert_num_queries(0, pear.tags.add)
 
     def test_require_pk(self):
         food_instance = self.food_model()