const dbName = 'testDB'; const collName = 'testColl'; const bucketsCollName = 'system.buckets.' + collName; const timeField = 'time'; const metaField = 'hostid'; // Connections.   const st = new ShardingTest({mongos: 2, shards: 2, rs: {nodes: 2}}); const mongos0 = st.s0.getDB(dbName); const mongos1 = st.s1.getDB(dbName); const shard0DB = st.shard0.getDB(dbName); const shard1DB = st.shard1.getDB(dbName);   // Insert some dummy data using 'mongos1' as the router, so that the cache is // initialized on the mongos while the collection is unsharded. assert.commandWorked( mongos1.adminCommand({shardCollection: `${dbName}.${collName}`, key: {_id: 1}})); assert.commandWorked(mongos1.getCollection(collName).insert({_id: "aaa"}));   // Drop and shard the collection with 'mongos0' as the router. assert(mongos0.getCollection(collName).drop());   const shardKey = { [metaField]: 1 } ; assert.commandWorked(mongos0.adminCommand({ shardCollection: `${dbName}.${collName}`, key: shardKey, timeseries: {timeField: timeField, metaField: metaField} }));   let cmdObj = {createIndexes: collName, indexes: [{key: {[timeField]: 1} , name: "index_on_time"}]}; assert.commandWorked(mongos1.runCommand(cmdObj));   st.stop();