Require the test helper directly instead of injecting it via ruby_opts

Rakefile

@@ -2,8 +2,6 @@ require "bundler/gem_tasks"
 require "rake/testtask"
 
 Rake::TestTask.new(:test) do |t|
-  t.libs << "test/lib"
-  t.ruby_opts << "-rhelper"
   t.test_files = FileList["test/**/test_*.rb"]
 end
 

test/drb/drbtest.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: false
-require 'test/unit'
+require_relative '../lib/helper'
 require 'envutil'
 require 'drb/drb'
 require 'drb/extservm'

test/drb/test_acl.rb

@@ -5,7 +5,7 @@
 # acltest.rb is copyrighted free software by Masatoshi SEKI.
 # You can redistribute it and/or modify it under the same terms as Ruby.
 
-require 'test/unit'
+require_relative '../lib/helper'
 require 'drb/acl'
 
 module DRbTests

test/drb/test_drbobject.rb

@@ -1,4 +1,4 @@
-require 'test/unit'
+require_relative '../lib/helper'
 require 'envutil'
 require 'drb'
 require 'drb/timeridconv'