Index does not seem to maintain expected sort order

[jusexton]

Problem

I am creating a compound index and specifying that items should be sorted in descending order by age. Mongomock does not seem to honor the sort order of the index.

Reproduce

import mongomock
import pymongo

client = mongomock.MongoClient()
collection = client['test_db']['test_collection']
collection.create_index([('name', pymongo.ASCENDING), ('age', pymongo.DESCENDING)])

data = [
    {'name': 'Foo', 'age': 5},
    {'name': 'Foo', 'age': 10}
]
collection.insert_many(data)

for person in collection.find({'name': 'Foo'}):
    print(person)

The above prints:

{'name': 'Foo', 'age': 5, '_id': ObjectId('64ef880e30cb3b4053d1c7c8')}
{'name': 'Foo', 'age': 10, '_id': ObjectId('64ef880e30cb3b4053d1c7c9')}

I would expect:

{'name': 'Foo', 'age': 10, '_id': ObjectId('64ef880e30cb3b4053d1c7c9')}
{'name': 'Foo', 'age': 5, '_id': ObjectId('64ef880e30cb3b4053d1c7c8')}

Am I doing anything wrong or is this a bug?

Version Info

pymongo = 4.4.0
mongomock = 4.1.2