Should check enum value on argument.

[Zapata]

Enum should work on arguments also.

With this code:

require 'rubygems'
require 'thor'

class EnumArgument < Thor

  argument :fruit, :enum => %w{banana, apple}

  desc 'salad fruit', 'Only like fruit salad'
  def salad
    puts fruit
  end
end

EnumArgument.start

We expect to have an error when executing:

$ ruby enum_argument.rb salad tomato

It does not with thor-0.18.1.