Update Ruby::Box context-mode test

Author: st0012

test/irb/test_irb.rb

@@ -994,6 +994,11 @@ class ContextModeTest < TestIRB::IntegrationTestCase
     def test_context_mode_ruby_box
       omit if RUBY_VERSION < "4.0.0"
       @envs['RUBY_BOX'] = '1'
+      # Ruby::Box now initializes RubyGems per box upstream. Avoid loading bundler context into test execution context.
+      %w[BUNDLER_SETUP BUNDLER_VERSION BUNDLE_BIN_PATH BUNDLE_GEMFILE RUBYOPT].each do |env|
+        @envs[env] = nil
+      end
+      @envs['RUBYLIB'] = Gem.loaded_specs.fetch('reline').full_require_paths.join(File::PATH_SEPARATOR)
 
       write_rc <<~'RUBY'
         IRB.conf[:CONTEXT_MODE] = 5
@@ -1007,11 +1012,13 @@ def test_context_mode_ruby_box
       RUBY
 
       output = run_ruby_file(timeout: TIMEOUT_SEC) do
+        type 'p gem_specification: defined?(Gem::Specification)'
         type 'class Integer; def +(_other) = 42; end'
         type 'p answer1: 1 + 2'
         type 'exit'
       end
 
+      assert_include(output, '{gem_specification: "constant"}')
       assert_include(output, '{answer1: 42}')
       assert_include(output, '{answer2: 3}')
     end