Add test for --external option.

    end

  end

  describe :external_classes do

    it "contains JavaScript builtins by default" do

      exts = parse().external_classes

      %w(Object String Number Boolean RegExp Function Array Arguments Date).each do |name|

        exts.should include(name)

      end

    end

    it "contains JavaScript builtin error classes by default" do

      exts = parse().external_classes

      exts.should include("Error")

      %w(Eval Range Reference Syntax Type URI).each do |name|

        exts.should include("#{name}Error")

      end

    end

    it "contains the special anything-goes Mixed type" do

      parse().external_classes.should include("Mixed")

    end

    it "can be used multiple times" do

      exts = parse("--external", "MyClass", "--external", "YourClass").external_classes

      exts.should include("MyClass")

      exts.should include("YourClass")

    end

    it "can be used with comma-separated list" do

      exts = parse("--external", "MyClass,YourClass").external_classes

      exts.should include("MyClass")

      exts.should include("YourClass")

    end

  end

  # Turns :attribute_name into "--option-name" or "--no-option-name"

  def opt(attr, negate=false)

    (negate ? "--no-" : "--") + attr.to_s.gsub(/_/, '-')