text: /**
   * Verifies that the $collStats aggregation stage includes the shard and hostname for each output
   * document when run via mongoS, and that the former is absent when run on a non-shard mongoD.
   */
  (function() {
      "use strict";
  
      // Test mongoD behaviour using the standalone started by resmoke.py.
      let testDB = db.getSiblingDB(jsTestName());
      let testColl = testDB.test;
  
      // getHostName() doesn't include port, db.getMongo().host is 127.0.0.1:<port>
      const hostName = (getHostName() + ":" + db.getMongo().host.split(":")[1]);
  
      // Test that the shard field is absent and the host field is present when run on mongoD.
      assert.eq(testColl
                    .aggregate([
                        {$collStats: {latencyStats: {histograms: true}}},
                        {$group: {_id: {shard: "$shard", host: "$host"}}}
                    ])
                    .toArray(),
                [{_id: {host: hostName}}]);
  
      // Test that both shard and hostname are present for $collStats results on a sharded cluster.
      const st = new ShardingTest({name: jsTestName(), shards: 2});
  
      st.stopBalancer();
  
      testDB = st.s.getDB(jsTestName());
      testColl = testDB.test;
  
      assert.commandWorked(testDB.dropDatabase());
  
      // Enable sharding on the test database.
      assert.commandWorked(testDB.adminCommand({enableSharding: testDB.getName()}));
  
      // Shard 'testColl' on {_id: 'hashed'}. This will automatically presplit the collection and
      // place chunks on each shard.
      assert.commandWorked(
          testDB.adminCommand({shardCollection: testColl.getFullName(), key: {_id: "hashed"}}));
  
      // Group $collStats result by $shard and $host to confirm that both fields are present.
      assert.eq(testColl
                    .aggregate([
                        {$collStats: {latencyStats: {histograms: true}}},
                        {$group: {_id: {shard: "$shard", host: "$host"}}},
                        {$sort: {_id: 1}}
                    ])
                    .toArray(),
                [
                  {_id: {shard: "shard0000", host: st.shard0.host}},
                  {_id: {shard: "shard0001", host: st.shard1.host}},
                ]);
  
      st.stop();
  })();