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_object_tree.rb
    path of file: ./repos/origami/test
    
    the code of the file until where you have to start completion: require 'minitest/autorun'
require 'stringio'

class TestPDFObjectTree < Minitest::Test

    def setup
        @pdf = PDF.new.append_page
        @contents = ContentStream.new("abc")
        @pdf.pages.first.Contents 
    
    def test_pdf_object_tree
        assert_instance_of Catalog, @pdf.Catalog
        assert_nil @pdf.Catalog.parent

        @pdf.each_object(recursive: true) do |obj|
            assert_kind_of Origami::Object, obj
            assert_equal obj.document, @pdf

            unless obj.indirect?
                assert_kind_of Origami::Object, obj.parent
                assert_equal obj.parent.document, @pdf
            end
        end