DRIVERS-2816 : Summary of necessary driver changes Modify the unified test runner to collect the cluster time from the internal MongoClient following initialData operations, and use it to advance cluster times of all session entities created during the subsequent test. See mongodb/specifications@fd6ae12 for implementation details. Context for other referenced/linked tickets SERVER-82353 addressed a correctness issue for sharded clusters, which requires gossipping the cluster time between mongos hsots (particularly the server used to create collections and other(s) used to execute transactions) in order to avoid a MigrationConflict error.