diff --git a/.gitignore b/.gitignore
index 7941b6dee2a35b..55a5659a8436ca 100644
--- a/.gitignore
+++ b/.gitignore
@@ -77,14 +77,12 @@
 **/vendor/bundle/ruby/*/gems/coderay-*/
 **/vendor/bundle/ruby/*/gems/colorize-*/
 **/vendor/bundle/ruby/*/gems/commander-*/
-**/vendor/bundle/ruby/*/gems/debug-*/
 **/vendor/bundle/ruby/*/gems/diff-lcs-*/
 **/vendor/bundle/ruby/*/gems/docile-*/
 **/vendor/bundle/ruby/*/gems/ecma-re-validator-*/
 **/vendor/bundle/ruby/*/gems/erubi-*/
 **/vendor/bundle/ruby/*/gems/hana-*/
 **/vendor/bundle/ruby/*/gems/highline-*/
-**/vendor/bundle/ruby/*/gems/irb-*/
 **/vendor/bundle/ruby/*/gems/jaro_winkler-*/
 **/vendor/bundle/ruby/*/gems/json-*/
 **/vendor/bundle/ruby/*/gems/json_schemer-*/
@@ -110,7 +108,6 @@
 **/vendor/bundle/ruby/*/gems/rbi-*/
 **/vendor/bundle/ruby/*/gems/rdoc-*/
 **/vendor/bundle/ruby/*/gems/regexp_parser-*/
-**/vendor/bundle/ruby/*/gems/reline-*/
 **/vendor/bundle/ruby/*/gems/rexml-*/
 **/vendor/bundle/ruby/*/gems/rspec-*/
 **/vendor/bundle/ruby/*/gems/rspec-core-*/
@@ -131,7 +128,6 @@
 !**/vendor/bundle/ruby/*/gems/sorbet-runtime-*/
 **/vendor/bundle/ruby/*/gems/spoom-*/
 **/vendor/bundle/ruby/*/gems/stackprof-*/
-**/vendor/bundle/ruby/*/gems/stringio-*/
 **/vendor/bundle/ruby/*/gems/strscan-*/
 **/vendor/bundle/ruby/*/gems/syntax_tree-*/
 **/vendor/bundle/ruby/*/gems/tapioca-*/
diff --git a/Library/Homebrew/Gemfile b/Library/Homebrew/Gemfile
index b4bedd6060e6e4..533593a96f4894 100644
--- a/Library/Homebrew/Gemfile
+++ b/Library/Homebrew/Gemfile
@@ -48,9 +48,7 @@ group :style, optional: true do
   gem "rubocop-sorbet", require: false
 end
 group :tests, optional: true do
-  gem "debug", require: false
   gem "parallel_tests", require: false
-  gem "psych", "< 5", require: false
   gem "rspec", require: false
   gem "rspec-github", require: false
   gem "rspec_junit_formatter", require: false
diff --git a/Library/Homebrew/Gemfile.lock b/Library/Homebrew/Gemfile.lock
index d5590b518180dd..04018f866b453b 100644
--- a/Library/Homebrew/Gemfile.lock
+++ b/Library/Homebrew/Gemfile.lock
@@ -10,9 +10,6 @@ GEM
     coderay (1.1.3)
     commander (4.6.0)
       highline (~> 2.0.0)
-    debug (1.9.2)
-      irb (~> 1.10)
-      reline (>= 0.3.8)
     diff-lcs (1.5.1)
     docile (1.4.0)
     elftools (1.3.0)
@@ -20,10 +17,6 @@ GEM
     erubi (1.12.0)
     hana (1.3.7)
     highline (2.0.3)
-    io-console (0.7.2)
-    irb (1.12.0)
-      rdoc
-      reline (>= 0.4.2)
     json (2.7.2)
     json_schemer (2.1.1)
       hana (~> 1.3)
@@ -54,19 +47,13 @@ GEM
     pry (0.14.2)
       coderay (~> 1.1)
       method_source (~> 1.0)
-    psych (4.0.6)
-      stringio
     public_suffix (5.0.5)
     racc (1.7.3)
     rainbow (3.1.1)
     rbi (0.1.10)
       prism (>= 0.18.0, < 0.25)
       sorbet-runtime (>= 0.5.9204)
-    rdoc (6.6.3.1)
-      psych (>= 4.0.0)
     regexp_parser (2.9.0)
-    reline (0.5.0)
-      io-console (~> 0.5)
     rexml (3.2.6)
     rspec (3.13.0)
       rspec-core (~> 3.13.0)
@@ -149,7 +136,6 @@ GEM
       sorbet-static-and-runtime (>= 0.5.10187)
       thor (>= 0.19.2)
     stackprof (0.2.26)
-    stringio (3.1.0)
     tapioca (0.13.3)
       bundler (>= 2.2.25)
       netrc (>= 0.11.0)
@@ -180,7 +166,6 @@ PLATFORMS
 DEPENDENCIES
   addressable
   bootsnap
-  debug
   json_schemer
   kramdown
   method_source
@@ -190,7 +175,6 @@ DEPENDENCIES
   patchelf
   plist
   pry
-  psych (< 5)
   rexml
   rspec
   rspec-github
diff --git a/Library/Homebrew/dev-cmd/tests.rb b/Library/Homebrew/dev-cmd/tests.rb
index 342f155f139d21..f99ab7e6a846ef 100644
--- a/Library/Homebrew/dev-cmd/tests.rb
+++ b/Library/Homebrew/dev-cmd/tests.rb
@@ -45,6 +45,8 @@ def run
         # Given we might be testing various commands, we probably want everything (except sorbet-static)
         Homebrew.install_bundler_gems!(groups: Homebrew.valid_gem_groups - ["sorbet"])
 
+        require "debug" if args.debug?
+
         HOMEBREW_LIBRARY_PATH.cd do
           setup_environment!
 
diff --git a/Library/Homebrew/standalone/init.rb b/Library/Homebrew/standalone/init.rb
index fafbaa2ab576c0..45368cb1fadc2b 100644
--- a/Library/Homebrew/standalone/init.rb
+++ b/Library/Homebrew/standalone/init.rb
@@ -39,6 +39,10 @@
   ENV["HOMEBREW_SKIP_INITIAL_GEM_INSTALL"] = "1"
 end
 
+if Pathname.new(RbConfig.ruby).to_s.include?("/vendor/portable-ruby/")
+  $LOAD_PATH.unshift "#{RbConfig::CONFIG["rubylibprefix"]}/gems/#{RbConfig::CONFIG["ruby_version"]}/gems/debug-1.6.3/lib"
+end
+
 unless $LOAD_PATH.include?(HOMEBREW_LIBRARY_PATH.to_s)
   # Insert the path after any existing Homebrew paths (e.g. those inserted by tests and parent processes)
   last_homebrew_path_idx = $LOAD_PATH.rindex do |path|
diff --git a/Library/Homebrew/test/migrator_spec.rb b/Library/Homebrew/test/migrator_spec.rb
index 87fadd5e955558..4494b919b73450 100644
--- a/Library/Homebrew/test/migrator_spec.rb
+++ b/Library/Homebrew/test/migrator_spec.rb
@@ -69,6 +69,8 @@
       tab.source["tap"] = "homebrew/core"
       tab.write
 
+      binding.b
+
       expect do
         described_class.new(new_formula, "oldname")
       end.to raise_error(Migrator::MigratorDifferentTapsError)
diff --git a/Library/Homebrew/test/spec_helper.rb b/Library/Homebrew/test/spec_helper.rb
index c36ea110f3482e..517acadb8cc260 100644
--- a/Library/Homebrew/test/spec_helper.rb
+++ b/Library/Homebrew/test/spec_helper.rb
@@ -29,7 +29,6 @@
 require "rspec/sorbet"
 require "rubocop/rspec/support"
 require "find"
-require "debug"
 require "timeout"
 
 $LOAD_PATH.unshift(File.expand_path("#{ENV.fetch("HOMEBREW_LIBRARY")}/Homebrew/test/support/lib"))
diff --git a/Library/Homebrew/vendor/bundle/bundler/setup.rb b/Library/Homebrew/vendor/bundle/bundler/setup.rb
index 913cc12511a2a3..5a696f1f252c65 100644
--- a/Library/Homebrew/vendor/bundle/bundler/setup.rb
+++ b/Library/Homebrew/vendor/bundle/bundler/setup.rb
@@ -38,17 +38,6 @@ def self.extension_api_version
 $:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/coderay-1.1.3/lib")
 $:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/highline-2.0.3/lib")
 $:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/commander-4.6.0/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/extensions/arm64-darwin-20/#{Gem.extension_api_version}/stringio-3.1.0")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/stringio-3.1.0/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/extensions/arm64-darwin-20/#{Gem.extension_api_version}/psych-4.0.6")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/psych-4.0.6/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/rdoc-6.6.3.1/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/extensions/arm64-darwin-20/#{Gem.extension_api_version}/io-console-0.7.2")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/io-console-0.7.2/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/reline-0.5.0/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/irb-1.12.0/lib")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/extensions/arm64-darwin-20/#{Gem.extension_api_version}/debug-1.9.2")
-$:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/debug-1.9.2/lib")
 $:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/diff-lcs-1.5.1/lib")
 $:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/docile-1.4.0/lib")
 $:.unshift File.expand_path("#{__dir__}/../#{RUBY_ENGINE}/#{Gem.ruby_api_version}/gems/elftools-1.3.0/lib")
diff --git a/completions/fish/brew.fish b/completions/fish/brew.fish
index c5ec5801a856e5..ecb629d6556426 100644
--- a/completions/fish/brew.fish
+++ b/completions/fish/brew.fish
@@ -1467,7 +1467,7 @@ __fish_brew_complete_arg 'test' -a '(__fish_brew_suggest_formulae_installed)'
 __fish_brew_complete_cmd 'tests' 'Run Homebrew\'s unit and integration tests'
 __fish_brew_complete_arg 'tests' -l changed -d 'Only runs tests on files that were changed from the master branch'
 __fish_brew_complete_arg 'tests' -l coverage -d 'Generate code coverage reports'
-__fish_brew_complete_arg 'tests' -l debug -d 'Display any debugging information'
+__fish_brew_complete_arg 'tests' -l debug -d 'Enable debugging using ruby/debug, or surface the standard `odebug` output'
 __fish_brew_complete_arg 'tests' -l fail-fast -d 'Exit early on the first failing test'
 __fish_brew_complete_arg 'tests' -l generic -d 'Run only OS-agnostic tests'
 __fish_brew_complete_arg 'tests' -l help -d 'Show this message'
diff --git a/completions/zsh/_brew b/completions/zsh/_brew
index 69bdbe7c35e896..e7536ef77e41f9 100644
--- a/completions/zsh/_brew
+++ b/completions/zsh/_brew
@@ -1817,7 +1817,7 @@ _brew_tests() {
   _arguments \
     '(--only)--changed[Only runs tests on files that were changed from the master branch]' \
     '--coverage[Generate code coverage reports]' \
-    '--debug[Display any debugging information]' \
+    '--debug[Enable debugging using ruby/debug, or surface the standard `odebug` output]' \
     '--fail-fast[Exit early on the first failing test]' \
     '--generic[Run only OS-agnostic tests]' \
     '--help[Show this message]' \
diff --git a/docs/Manpage.md b/docs/Manpage.md
index a001fde3dfd1d8..b4b42f9e8c25ef 100644
--- a/docs/Manpage.md
+++ b/docs/Manpage.md
@@ -2650,6 +2650,10 @@ Run Homebrew's unit and integration tests.
 : Include tests that use the GitHub API and tests that use any of the taps for
   official external commands.
 
+`--debug`
+
+: Enable debugging using ruby/debug, or surface the standard `odebug` output.
+
 `--changed`
 
 : Only runs tests on files that were changed from the master branch.
diff --git a/manpages/brew.1 b/manpages/brew.1
index 9716af71e1bee5..2415dca39a57ad 100644
--- a/manpages/brew.1
+++ b/manpages/brew.1
@@ -1687,6 +1687,9 @@ Run only OS\-agnostic tests\.
 \fB\-\-online\fP
 Include tests that use the GitHub API and tests that use any of the taps for official external commands\.
 .TP
+\fB\-\-debug\fP
+Enable debugging using ruby/debug, or surface the standard \fBodebug\fP output\.
+.TP
 \fB\-\-changed\fP
 Only runs tests on files that were changed from the master branch\.
 .TP