This test https://github.com/DmitryLukyanov/mongo-csharp-driver/commit/14955fef00249202923def96665cec546a95932c#diff-e77a195401fcf5cb1245e1e5d264d1d5R30 creates indexes (including unique), but doesn't remove them after launching. It should be fixed, otherwise, some other test will fail since they don't expect any indexes on test collection.