Произвел проверку на платформах: 
* p10-education-10.1-x86-64
* p10-education-10.1-x86-64-kde
* p10-kworkstation-10.1-x86-64
* p10-server-10-x86-64
* p10-workstation-10-x86-64

Версия пакета: 
* gem-libxml-ruby-3.2.3-alt2

Шаги воспроизведения:
1. Установить пакет
# apt-get install gem-libxml-ruby
2. Перейти в папку с тестами и запустить их:

$ cd /usr/lib/ruby/gems/*/gems/libxml-ruby-*/test

$ ruby test_suite.rb

Ожидаемый результат:
Тесты проходят
$ ruby test_suite.rb
Run options: --seed 7217

# Running:

..........................................    ELEMENT bands
      ATTRIBUTE genre
        TEXT
          content=metal
      ELEMENT m#C3#B6tley_cr#C3#BCe
        ATTRIBUTE country
          TEXT
            content=us
        TEXT
          content=M#C3#B6tley Cr#C3#BCe is an American heavy metal...
      ELEMENT iron_maiden
        ATTRIBUTE country
          TEXT
            content=uk
        TEXT
          content=Iron Maiden is a British heavy metal ban...
.........Parser.register_error_handler is deprecated.  Use Error.set_handler instead
...............Thread completed
...F..........................................F....................................................................F...............DOCUMENT
version=1.0
encoding=utf-8
URL=/usr/lib/ruby/gems/2.7.0/gems/libxml-rub...
standalone=true
  ELEMENT bands
    ATTRIBUTE genre
      TEXT
        content=metal
    ELEMENT m#C3#B6tley_cr#C3#BCe
      ATTRIBUTE country
        TEXT interned
          content=us
      TEXT
        content=M#C3#B6tley Cr#C3#BCe is an American heavy metal...
    ELEMENT iron_maiden
      ATTRIBUTE country
        TEXT interned
          content=uk
      TEXT
        content=Iron Maiden is a British heavy metal ban...
.....................................................................................................................................................

Finished in 4.359658s, 79.3640 runs/s, 9696.1732 assertions/s.

  1) Failure:
TestParser#test_error [/usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.1.0/test/test_parser.rb:278]:
Expected: 20
  Actual: 18

  2) Failure:
TestReader#test_bytes_consumed [/usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.1.0/test/test_reader.rb:254]:
Expected: 428
  Actual: 416

  3) Failure:
TestParserContext#test_parse_error [/usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.1.0/test/test_parser_context.rb:188]:
Expected: 17
  Actual: 0

346 runs, 42272 assertions, 3 failures, 0 errors, 0 skips


Фактический результат: 
$ ruby test_suite.rb
There was an error while trying to write to `/usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.2.3/Gemfile.lock`. It is likely that you need to grant write permissions for that path.

При попытке запустить от рут:
# ruby test_suite.rb
Traceback (most recent call last):
	6: from test_suite.rb:8:in `<main>'
	5: from /usr/lib/ruby/rubygems/core_ext/kernel_require.rb:83:in `require'
	4: from /usr/lib/ruby/rubygems/core_ext/kernel_require.rb:83:in `require'
	3: from /usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.2.3/test/test_attr.rb:3:in `<top (required)>'
	2: from /usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.2.3/test/test_attr.rb:3:in `require_relative'
	1: from /usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.2.3/test/test_helper.rb:6:in `<top (required)>'
/usr/lib/ruby/gems/2.7.0/gems/libxml-ruby-3.2.3/test/test_helper.rb:6:in `require': cannot load such file -- minitest/autorun (LoadError)