attempt.rb

require 'rails_helper'

describe 'MultiValueInput', type: :input do

  class Foo
    extend ActiveModel::Naming
    include ActiveModel::Conversion
    include ActiveModel::Validations
    def persisted?; false; end
    attr_accessor :bar
  end

  include RSpec::Rails::HelperExampleGroup

  def input_for(object, attribute_name, options={})
    helper.simple_form_for object, url: '' do |f|
      f.input attribute_name, options
    end
  end
end