code: function (cb) {
            if (opts.dropCollection) {
              db.listCollections({name: collectionName})
                .toArray(function (err, items) {
                  if (err) return cb(err)
                  if (items.length) return coll.drop(cb)
                  cb()
                })
            } else cb()
          }
docs: Drop collection if option is set and collection exists