Inconsistent behavior of list_collection_names() with and without filter

[adrienballsonos]

Summary

When calling list_collection_names() with a filter, mongomock will list "created" and "non-created" collections as opposed to what it does when no filter is provided in which case only "created" collections are listed.

Here is a small test which exposes the isssue:

def test_list_collection_names():
    client = mongomock.MongoClient()
    db = client["my_db"]
    assert db.list_collection_names() == []  # OK
    # Run an update operation on a non existent collection
    db["my_collection"].update_many({}, {"$set": {"a": 1}})
    assert db.list_collection_names() == []  # OK
    assert db.list_collection_names(filter={"name": "my_collection"}) == []  # KO

This test produces the following output:

def test_list_collection_names():
        client = mongomock.MongoClient()
        db = client["my-db"]
        assert db.list_collection_names() == []
        db["non_existing_collection"].update_many({}, {"$set": {"a": 1}})
        assert db.list_collection_names() == []
>       assert db.list_collection_names(filter={"name": "non_existing_collection"}) == []
E       AssertionError: assert ['non_existing_collection'] == []
E         Left contains one more item: 'non_existing_collection'
E         Full diff:
E         - []
E         + ['non_existing_collection']

When looking at the underlying code, mongomock relies on self._get_created_collections() when no filter is provided (here), whereas it uses self._store._collections when a filter is passed (here). I would have expected self._get_created_collections() to be used in both cases.

The current behavior does not match the one of MongoDB.

Python version: 3.9.9
mongomock version: 4.1.2