You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: message_tag_spec.rb
    path of file: ./repos/savon/spec/savon/features
    
    the code of the file until where you have to start completion: # frozen_string_literal: true
require 'spec_helper'

RSpec.describe Savon do

  it 'knows the message tag for :authentication' do
    message_tag = message_tag_for(:authentication, :authenticate)
    expect(message_tag).to eq(['http://v1_0.ws.auth.order.example.com/', 'authenti
    
  def message_tag_for(fixture, operation_name)
    globals     = Savon::GlobalOptions.new(:log => false)
    wsdl        = Wasabi::Document.new Fixture.wsdl(fixture)
    operation   = Savon::Operation.create(operation_name, wsdl, globals)
    request_xml = operation.build.to_s

    nsid, local = extract_message_tag_from_request(request_xml)
    namespace   = extract_namespace_from_request(nsid, request_xml)

    [namespace, local]
  end