Verifying that at least one oplog entry has replicated

These steps must be performed on each secondary in the replica set:

1. Use the mongo shell to connect to each secondary in the replica set:

mongo --host <address of secondary>

2. Once connected to the secondary, run the rs.status(); command and check the values of the optimes::appliedOpTime::t key.
3. Repeat this for each secondary and confirm that the t value is greater than -1. This tells us that at least one oplog entry has replicated from the primary to all secondaries.