It's annoying to have to specify a different org.mongodb.test.uri system property every time you want to test against a replica set, especially when executing single tests in an IDE. This could be made easier by having the testing framework (if no system property is provided) interrogate the server running at localhost:27017 to determine whether it's a replica set member, and if it is then change the default URI to mongodb://localhost/?replicaSet=<setName from isMaster response>.