code: function createInvalidInterfaceError(message, ui) {
    var err = new Error(message);
    err.code = 'ERR_MOCHA_INVALID_INTERFACE';
    err.interface = ui;
    return err;
  }
docs: Creates an error object to be thrown when the interface specified in the options was not found.
  
  @public
  @param {string} message - Error message to be displayed.
  @param {string} ui - User-specified interface value.
  @returns {Error} instance detailing the error condition