```ruby
module Litmus
  class EmailTest < Test
    def self.list
      super.reject{|test| test["service"] != 'email'}
    end

    def self.create(email={}, name = nil, sandbox = false)
      builder = Builder::XmlMarkup.new
      builder.instruct! :xml, :version=>"1.0"
      builder.test_set do |test_set|
        test_set.use_defaults true
        test_set.save_defaults false
        test_set.name name if name
        test_set.sandbox true if sandbox
        
        unless email.empty?
          test_set.email_source do |email_source|
            email_source.subject email[:subject]
            email_source.body do |body|
              body.cdata! email[:body]
            end
          end
        end
      end
      post('/emails.xml', :body => builder.target!, :headers => {"Content-type" => "application/xml"})["test_set"]
    end
  end
end
```

Add support for application codes
user
```ruby
module Litmus
  class EmailTest < Test
    def self.list
      super.reject{|test| test["service"] != 'email'}
    end

    def self.create(email={}, name = nil, sandbox = false, application_codes=[])
      builder = Builder::XmlMarkup.new
      builder.instruct! :xml, :version=>"1.0"
      builder.test_set do |test_set|
        if application_codes
          application_codes.each do |application_code|
            test_set.tag!("applications", {type: "array"}) do |applications|
              applications.application do |application|
                application.code application_code
              end
            end
          end
        end

        test_set.use_defaults application_codes.empty?
        test_set.save_defaults false
        test_set.name name if name
        test_set.sandbox true if sandbox
        
        unless email.empty?
          test_set.email_source do |email_source|
            email_source.subject email[:subject]
            email_source.body do |body|
              body.cdata! email[:body]
            end
          end
        end
      end
      post('/emails.xml', :body => builder.target!, :headers => {"Content-type" => "application/xml"})["test_set"]
    end
  end
end
```
assistant