We want to come up with a plan for how we can comprehensively test replication components in unit tests. In order to do this we want to define the types of tests we would like to be able to accomplish and then determine what fixtures / mocks we would need to make that happen.

This ticket should focus on the thought experiment of what use cases we want to be able to test for different replication components (replication coordinator, oplog, initial sync, transactions, etc) and if there is any missing infrastructure we need to create to allow them to happen.