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: test_io_buffer.rb
    path of file: ./repos/truffleruby/test/mri/tests/ruby
    
    the code of the file until where you have to start completion: # frozen_string_literal: false

require 'tempfile'

class TestIOBuffer < Test::Unit::TestCase
  # TruffleRuby: no IO::Buffer yet
  # experimental = Warning[:experimental]
  # begin
  #   Warning[:experimental] 
    
  def test_new_readonly
    buffer = IO::Buffer.new(128, IO::Buffer::INTERNAL|IO::Buffer::READONLY)
    assert buffer.readonly?

    assert_raise IO::Buffer::AccessError do
      buffer.set_string("")
    end

    assert_raise IO::Buffer::AccessError do
      buffer.set_string("!", 1)
    end
  end