Feature: mongodb as replica set (single node)

What are you trying to do?

Unit testing of Mongodb transactions.

Why should it be done this way?

mongomock can often be used in unit testing of mongodb-related functionality. It's faster and easier than using docker containers for such tests. But perhaps one of the most important scenarios in which mongomock is not applicable is testing the functionality using MongoDB transactions. At the moment, transaction mocking is not implemented in mongomock. But even if support for this was implemented there, such sensitive functionality (using transactions) would like to be checked "naturally". But as you know, transactions are possible only for replica sets, which the default MongoDB container is not. It is possible to configure mongodb as a replicaset (although with one node, but I think this is not critical for testing).

If you find this functionality useful here in the public, I can provide a PR (either as a separate Mongodb container, or extend the current MongoDbContainer with configuration options). What do you think about it?

Start with the current MongoDbContainer and the default MongoDB container setup. Check how a single-node replica set can be configured for container-based tests, then verify that MongoDB transactions can run through the resulting container. Done means users can use the container to test transaction functionality without configuring an external replica set.