Presumably the assert.neq() here should be on dbs[i], not just 'dbs'.

https://github.com/mongodb/mongo/blob/73d3473f/jstests/sharding/drop_sharded_db.js#L42

    // Drop the non-suffixed db and ensure that it is the only one that was dropped.
    dbA.dropDatabase();
    var dbs = mongos.getDBNames();
    for (var i = 0; i < dbs.length; i++) {
        assert.neq(dbs, "" + dbA);
    }

Also, we should assert.commandWorked() on the dropDatabase().

Failing to assert.commandWorked() can lead to the test failing on a later line, as in BF-4953:

https://github.com/mongodb/mongo/blob/73d3473f/jstests/sharding/drop_sharded_db.js#L45

    assert.eq(0, config.databases.count({_id: dbA.getName()}));

It's particularly misleading because the for-loop with the 'dbs' bug fails to catch when the db was not actually deleted, so it seems like an issue with the count().