Having something like "assert number of queries" on mongo

I was thinking to open a ticket in Jira, but I thought to first post it here to open it up for discussion. 

It would be a nice thing to be able, while testing some services doing several operations, to be able to test that it makes a certain number of calls to the database (and eventually optimize), like it is possible with SQL DBs. I searched for it and found nothing.

I think it could still be possible to use some db infos in mongo, but it may interesting to have a helper for that (maybe simply implemented at the driver level ?)