Idiot forgot datetime was immutable

metrik/targets/mongo.py

@@ -38,8 +38,7 @@ class MongoTarget(Target):
         # Because MongoDB isn't microsecond-accurate, we need to set the
         # microseconds to 0 to ensure consistency
         present_deref = present if present is not None else datetime.now()
-        present_deref.replace(microsecond=0)
-        id_dict['_created_at'] = present_deref
+        id_dict['_created_at'] = present_deref.replace(microsecond=0)
 
         with self.get_db() as db:
             return db[self.collection].insert_one(id_dict).inserted_id

test/targets/test_mongo_target.py

@@ -54,8 +54,8 @@ class MongoTargetTest(MongoTest):
         r = t.retrieve()
         self.assertGreaterEqual(present, r['_created_at'])
 
-        one_second_past = present - timedelta(seconds=1)
+        second_prior = (present - timedelta(seconds=1)).replace(microsecond=0)
         t = MongoTarget('test_collection', 1235)
-        t.persist({}, present=one_second_past)
+        t.persist({}, present=second_prior)
         r = t.retrieve()
-        self.assertEqual(one_second_past, r['_created_at'])
+        self.assertEqual(second_prior, r['_created_at'])