/usr/lib/ is in ruby-test-unit 2.5.5-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/
/usr/lib/ruby/vendor_ruby/
/usr/lib/ruby/vendor_ruby/test/
/usr/lib/ruby/vendor_ruby/test/unit.rb
/usr/lib/ruby/vendor_ruby/test/unit/
/usr/lib/ruby/vendor_ruby/test/unit/assertions.rb
/usr/lib/ruby/vendor_ruby/test/unit/testcase.rb
/usr/lib/ruby/vendor_ruby/test/unit/assertionfailederror.rb
/usr/lib/ruby/vendor_ruby/test/unit/code-snippet-fetcher.rb
/usr/lib/ruby/vendor_ruby/test/unit/priority.rb
/usr/lib/ruby/vendor_ruby/test/unit/error.rb
/usr/lib/ruby/vendor_ruby/test/unit/testsuitecreator.rb
/usr/lib/ruby/vendor_ruby/test/unit/exceptionhandler.rb
/usr/lib/ruby/vendor_ruby/test/unit/attribute-matcher.rb
/usr/lib/ruby/vendor_ruby/test/unit/fixture.rb
/usr/lib/ruby/vendor_ruby/test/unit/diff.rb
/usr/lib/ruby/vendor_ruby/test/unit/pending.rb
/usr/lib/ruby/vendor_ruby/test/unit/attribute.rb
/usr/lib/ruby/vendor_ruby/test/unit/testsuite.rb
/usr/lib/ruby/vendor_ruby/test/unit/autorunner.rb
/usr/lib/ruby/vendor_ruby/test/unit/util/
/usr/lib/ruby/vendor_ruby/test/unit/util/backtracefilter.rb
/usr/lib/ruby/vendor_ruby/test/unit/util/method-owner-finder.rb
/usr/lib/ruby/vendor_ruby/test/unit/util/output.rb
/usr/lib/ruby/vendor_ruby/test/unit/util/procwrapper.rb
/usr/lib/ruby/vendor_ruby/test/unit/util/observable.rb
/usr/lib/ruby/vendor_ruby/test/unit/version.rb
/usr/lib/ruby/vendor_ruby/test/unit/failure.rb
/usr/lib/ruby/vendor_ruby/test/unit/color.rb
/usr/lib/ruby/vendor_ruby/test/unit/data.rb
/usr/lib/ruby/vendor_ruby/test/unit/fault-location-detector.rb
/usr/lib/ruby/vendor_ruby/test/unit/collector/
/usr/lib/ruby/vendor_ruby/test/unit/collector/xml.rb
/usr/lib/ruby/vendor_ruby/test/unit/collector/descendant.rb
/usr/lib/ruby/vendor_ruby/test/unit/collector/objectspace.rb
/usr/lib/ruby/vendor_ruby/test/unit/collector/load.rb
/usr/lib/ruby/vendor_ruby/test/unit/collector/dir.rb
/usr/lib/ruby/vendor_ruby/test/unit/omission.rb
/usr/lib/ruby/vendor_ruby/test/unit/color-scheme.rb
/usr/lib/ruby/vendor_ruby/test/unit/testresult.rb
/usr/lib/ruby/vendor_ruby/test/unit/ui/
/usr/lib/ruby/vendor_ruby/test/unit/ui/testrunner.rb
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/usr/lib/ruby/vendor_ruby/test/unit/ui/testrunnerutilities.rb
/usr/lib/ruby/vendor_ruby/test/unit/ui/console/
/usr/lib/ruby/vendor_ruby/test/unit/ui/console/outputlevel.rb
/usr/lib/ruby/vendor_ruby/test/unit/ui/console/testrunner.rb
/usr/lib/ruby/vendor_ruby/test/unit/ui/testrunnermediator.rb
/usr/lib/ruby/vendor_ruby/test/unit/ui/xml/
/usr/lib/ruby/vendor_ruby/test/unit/ui/xml/testrunner.rb
/usr/lib/ruby/vendor_ruby/test/unit/runner/
/usr/lib/ruby/vendor_ruby/test/unit/runner/xml.rb
/usr/lib/ruby/vendor_ruby/test/unit/runner/emacs.rb
/usr/lib/ruby/vendor_ruby/test/unit/runner/console.rb
/usr/lib/ruby/vendor_ruby/test/unit/notification.rb
/usr/lib/ruby/vendor_ruby/test/unit/collector.rb
/usr/lib/ruby/vendor_ruby/test-unit.rb