code: function messageFormat (type, inspect) {
    var msg = this.detailed
      ? 'expect %s `%s`, but %s `%s` given'
      : 'expect `%s`, but `%s` given'
    return this.detailed
      ? util.format(msg, type.expected, inspect.expected, type.actual, inspect.actual)
      : util.format(msg, type.expected, type.actual)
  }
docs: > Default message formatting function.
  
  @param  {Object} `type`
  @param  {Object} `inspect`
  @return {String}