code: function dropCollections (db, each, fn) {
    if (each && !fn) { fn = each; each = null }
    var conn = db.connection
      , cols = Object.keys(conn.collections)
  
    cols.forEach(function (name, k) {
      console.log('name: ', name, k)
      conn.collections[name].drop(function (err) {
        if (err == 'ns not found') {
          err = null
        }
        each && each(err, name)
      })
    })
    fn && fn(null)
  }
docs: Drop all collections in a database