Comment out this return to simulate a refresh failing for a reason other than the sessions collection not existing, e.g. interrupted by a stepdown. Then run this test (the test file must have a name that sorts after "config"): // Note this requires a jstest name that is sorted "after" the shard id "config" because that is // used as the shard name for the non config shard and this relies on the the "config" shard being // the "first" shard in a sorted order. const st = new ShardingTest({shards: 2, configShard: true}); const configShardName = st.shard0.shardName; const otherShardName = st.shard1.shardName; // // Transition config shard to dedicated mode, which requires draining config.system.sessions. // let removeRes = assert.commandWorked(st.s.adminCommand({transitionToDedicatedConfigServer: 1})); assert.eq(removeRes.state, "started", tojson(removeRes)); assert.commandWorked(st.s.adminCommand({ moveChunk: "config.system.sessions", find: {_id: 0}, to: otherShardName, _waitForDelete: true })); removeRes = assert.commandWorked(st.s.adminCommand({transitionToDedicatedConfigServer: 1})); assert.eq(removeRes.state, "completed", tojson(removeRes)); // // Transition back to config shard mode and trigger a session cache refresh, which will fail with // InvalidUUID and create a new local config.system.sessions collection on the config server. // assert.commandWorked(st.s.adminCommand({transitionFromDedicatedConfigServer: 1})); // Fails with InvalidUUID. assert.commandWorked(st.configRS.getPrimary().adminCommand({refreshLogicalSessionCacheNow: 1})); st.stop();