diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7929a9840..5230ca2cf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,12 +8,16 @@ jobs:
     runs-on: ubuntu-latest
     name: Ruby ${{ matrix.ruby }} tests
     strategy:
+      fail-fast: false
       matrix:
-        ruby: [2.3, 2.4, 2.5, 2.6, 2.7, jruby-9.3]
+        # '4' is a prefix match resolved against the version list baked into the
+        # setup-ruby commit pinned below, so it only tracks new 4.x releases as far
+        # as that pin. Bump the pin to pick up newer ones.
+        ruby: ['2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3', '3.4', '4.0.5', '4', 'jruby-9.3']
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@a37ce9120846195fa4ece8f58b268e6043cb2f26 # v3
       - name: Setup ruby
-        uses: ruby/setup-ruby@v1
+        uses: ruby/setup-ruby@95ef2b042f9d7a56d8268cba8559e2842e2ad01b # v1.321.0
         with:
           ruby-version: ${{ matrix.ruby }}
       - run: ./scripts/build
diff --git a/.github/workflows/pr-review.yml b/.github/workflows/pr-review.yml
deleted file mode 100644
index 5239309ef..000000000
--- a/.github/workflows/pr-review.yml
+++ /dev/null
@@ -1,27 +0,0 @@
-name: PR Review
-
-on:
-  pull_request:
-    types:
-      - opened
-      - repoened
-      - edited
-      - synchronize
-      - labeled
-      - unlabeled
-
-concurrency: 
-  group: ${{ github.workflow }} - ${{ github.ref }}
-  cancel-in-progress: true
-
-jobs:
-  label-checker:
-    runs-on: ubuntu-latest
-    name: Label Checker
-    steps:
-      - name: Check Labels
-        uses: docker://agilepathway/pull-request-label-checker:latest
-        with:
-          one_of: V2
-          repo_token: ${{ secrets.GITHUB_TOKEN }}
- 
\ No newline at end of file
diff --git a/lib/recurly_v2/xml/nokogiri.rb b/lib/recurly_v2/xml/nokogiri.rb
index 8853b8994..04b55b47c 100644
--- a/lib/recurly_v2/xml/nokogiri.rb
+++ b/lib/recurly_v2/xml/nokogiri.rb
@@ -18,10 +18,10 @@ def each_element xpath = nil
         elements.each { |el| yield el }
       end
 
-      def each element = root
+      def each element = root, &block
         element.elements.each do |el|
-          yield el
-          each el, &Proc.new
+          block.call el
+          each el, &block
         end
       end
 
diff --git a/lib/recurly_v2/xml/rexml.rb b/lib/recurly_v2/xml/rexml.rb
index 7c25d5564..741f47812 100644
--- a/lib/recurly_v2/xml/rexml.rb
+++ b/lib/recurly_v2/xml/rexml.rb
@@ -19,10 +19,10 @@ def each_element xpath = nil
         root.each_element(xpath) { |el| yield el }
       end
 
-      def each element = root
+      def each element = root, &block
         element.each_element do |el|
-          yield el
-          each el, &Proc.new
+          block.call el
+          each el, &block
         end
       end
 
diff --git a/recurly.gemspec b/recurly.gemspec
index c3f89751e..8e0201b97 100644
--- a/recurly.gemspec
+++ b/recurly.gemspec
@@ -25,10 +25,24 @@ Gem::Specification.new do |s|
     s.add_development_dependency 'nokogiri', '~> 1.8', '>= 1.8.2'
   end
 
-  s.add_development_dependency 'rake', '~> 11.3'
-  s.add_development_dependency 'minitest', '~> 5.8', '>= 5.8.0'
+  # logger left the default gems in Ruby 4.0; spec_helper requires it.
+  s.add_development_dependency 'logger'
+  # rake 11 requires ostruct, gone from Ruby 4.0's default gems.
+  s.add_development_dependency 'rake', '>= 11.3'
+  # Held to the 5.x line: minitest 6 needs Ruby >= 3.2, dropped the global must_*
+  # expectations this suite is written in, and moved Minitest::Mock to a gem that
+  # itself needs Ruby >= 3.1 — none of which the old half of the matrix can meet.
+  s.add_development_dependency 'minitest', '~> 5.8'
+  # Restores must_* if a bundled minitest 6 wins activation over the pin above.
+  s.add_development_dependency 'minitest-global_expectations'
+  # On Ruby 4.0 the bundled minitest 6 does win, and it no longer ships
+  # Minitest::Mock. Earlier Rubies keep getting Mock from minitest 5 itself.
+  if RUBY_VERSION >= '4.0'
+    s.add_development_dependency 'minitest-mock'
+  end
   s.add_development_dependency 'addressable', '~> 2.4', '>= 2.4.0'
-  s.add_development_dependency 'webmock', '~> 2.3', '>= 2.3.2'
+  # webmock 2.x requires base64, gone from Ruby 3.4's default gems.
+  s.add_development_dependency 'webmock', '>= 2.3.2'
   s.add_development_dependency 'simplecov', '~> 0'
 
   if RUBY_PLATFORM != 'java' && !ENV['CI']
diff --git a/spec/environment.rb b/spec/environment.rb
index 4d76a48eb..2d276afeb 100644
--- a/spec/environment.rb
+++ b/spec/environment.rb
@@ -3,8 +3,12 @@
 require 'stringio'
 old_stderr, $stderr = $stderr, StringIO.new
 at_exit do
-  $stderr.rewind
-  $stderr.lines.each { |line| old_stderr.puts line if line.include? lib }
+  # Warnings from anywhere but lib are noise, but suppressing them unconditionally
+  # also swallows load errors and leaves a failing run with no output at all.
+  failing = !$!.nil? && !($!.is_a?(SystemExit) && $!.success?)
+  buffered, $stderr = $stderr, old_stderr
+  buffered.rewind
+  buffered.each_line { |line| old_stderr.puts line if failing || line.include?(lib) }
 end
 
 case ENV['XML']
diff --git a/spec/recurly_v2/adjustment_spec.rb b/spec/recurly_v2/adjustment_spec.rb
index 0c1c531d6..9fe79b840 100644
--- a/spec/recurly_v2/adjustment_spec.rb
+++ b/spec/recurly_v2/adjustment_spec.rb
@@ -85,7 +85,7 @@
       juris_detail.tax_in_cents[:USD].must_equal 115
       juris_detail.rate.must_equal 0.056
       juris_detail.description.must_equal 'Sales Tax'
-      juris_detail.jurisdiction_name.must_equal nil
+      juris_detail.jurisdiction_name.must_be_nil
     end
 
     it "must raise an exception when unavailable" do
@@ -107,7 +107,7 @@
       stub_api_request :get, 'adjustments/abcdef1234567890', 'adjustments/show-200-nosub'
 
       adjustment = Adjustment.find 'abcdef1234567890'
-      adjustment.subscription.must_equal nil
+      adjustment.subscription.must_be_nil
     end
 
     describe '#marshal_dump' do
@@ -117,7 +117,7 @@
         adjustment = Adjustment.find 'abcdef1234567890'
         adjustment_from_dump = Marshal.load(Marshal.dump(adjustment))
 
-        adjustment.instance_variables.must_equal adjustment_from_dump.instance_variables
+        adjustment.instance_variables.sort.must_equal adjustment_from_dump.instance_variables.sort
       end
 
       it 'must return the same values' do
diff --git a/spec/recurly_v2/api/errors_spec.rb b/spec/recurly_v2/api/errors_spec.rb
index 97553fc46..6dc630aa7 100644
--- a/spec/recurly_v2/api/errors_spec.rb
+++ b/spec/recurly_v2/api/errors_spec.rb
@@ -8,12 +8,12 @@
       let(:error) { RecurlyV2::API::ResponseError.new nil, nil }
 
       it "must return nil" do
-        error.send(:xml).must_equal nil
+        error.send(:xml).must_be_nil
       end
     end
 
     describe "when response assigned" do
-      let(:response) { MiniTest::Mock.new }
+      let(:response) { Minitest::Mock.new }
       let(:error) { RecurlyV2::API::ResponseError.new nil, response }
 
       describe "when xml already cached" do
@@ -28,7 +28,7 @@
         before { response.expect :body, nil }
 
         it "must return nil" do
-          error.send(:xml).must_equal nil
+          error.send(:xml).must_be_nil
         end
       end
 
@@ -36,7 +36,7 @@
         before { 2.times { response.expect :body, '' } }
 
         it "must return nil" do
-          error.send(:xml).must_equal nil
+          error.send(:xml).must_be_nil
         end
       end
 
@@ -54,7 +54,7 @@
         before { 3.times { response.expect :body, html } }
 
         it "must return nil" do
-          error.send(:xml).must_equal nil
+          error.send(:xml).must_be_nil
         end
       end
     end
diff --git a/spec/recurly_v2/billing_info_spec.rb b/spec/recurly_v2/billing_info_spec.rb
index 394cf986f..b43432dc0 100644
--- a/spec/recurly_v2/billing_info_spec.rb
+++ b/spec/recurly_v2/billing_info_spec.rb
@@ -129,7 +129,7 @@
 
       it "is accessible as an attribute" do
         billing_info_without_cc_bin_country = BillingInfo.find 'without-cc-bin'
-        billing_info_without_cc_bin_country.cc_bin_country.must_equal nil
+        billing_info_without_cc_bin_country.cc_bin_country.must_be_nil
 
         billing_info_with_cc_bin_country = BillingInfo.find 'with-cc-bin'
         billing_info_with_cc_bin_country.cc_bin_country.must_equal 'US'
@@ -229,7 +229,7 @@
       billing_info = BillingInfo.find 'abcdef1234567890'
       billing_info_from_dump = Marshal.load(Marshal.dump(billing_info))
 
-      billing_info.instance_variables.must_equal billing_info_from_dump.instance_variables
+      billing_info.instance_variables.sort.must_equal billing_info_from_dump.instance_variables.sort
     end
 
     it 'must return the same values' do
diff --git a/spec/recurly_v2/credit_payment_spec.rb b/spec/recurly_v2/credit_payment_spec.rb
index fb795cb64..613670219 100644
--- a/spec/recurly_v2/credit_payment_spec.rb
+++ b/spec/recurly_v2/credit_payment_spec.rb
@@ -34,7 +34,7 @@
       credit_payment = CreditPayment.find('12345')
 
       credit_payment_from_dump = Marshal.load(Marshal.dump(credit_payment))
-      credit_payment.instance_variables.must_equal credit_payment_from_dump.instance_variables
+      credit_payment.instance_variables.sort.must_equal credit_payment_from_dump.instance_variables.sort
     end
 
     it 'must return the same values' do
diff --git a/spec/recurly_v2/gift_card_spec.rb b/spec/recurly_v2/gift_card_spec.rb
index 169800f00..d60e3a8cc 100644
--- a/spec/recurly_v2/gift_card_spec.rb
+++ b/spec/recurly_v2/gift_card_spec.rb
@@ -36,8 +36,8 @@
       gift_card.balance_in_cents.must_equal 1_000
       gift_card.currency.must_equal "USD"
       gift_card.created_at.must_equal DateTime.parse("2016-07-28T00:01:48Z")
-      gift_card.canceled_at.must_equal nil
-      gift_card.delivered_at.must_equal nil
+      gift_card.canceled_at.must_be_nil
+      gift_card.delivered_at.must_be_nil
       gift_card.id.must_equal 2004005808969875135
       gift_card.product_code.must_equal "gift_card"
       gift_card.redeemed_at.must_equal DateTime.parse("2016-07-28T00:01:46Z")
@@ -54,7 +54,7 @@
 
       delivery.must_be_instance_of RecurlyV2::Delivery
       delivery.method.must_equal "email"
-      delivery.deliver_at.must_equal nil
+      delivery.deliver_at.must_be_nil
       delivery.email_address.must_equal "john@example.com"
       delivery.first_name.must_equal "John"
       delivery.last_name.must_equal "Smith"
@@ -64,7 +64,7 @@
       address = delivery.address
 
       address.address1.must_equal "400 Alabama St"
-      address.address2.must_equal nil
+      address.address2.must_be_nil
       address.city.must_equal "San Francisco"
       address.state.must_equal "CA"
       address.zip.must_equal "94110"
diff --git a/spec/recurly_v2/resource_spec.rb b/spec/recurly_v2/resource_spec.rb
index 2102673c5..3fb8b060c 100644
--- a/spec/recurly_v2/resource_spec.rb
+++ b/spec/recurly_v2/resource_spec.rb
@@ -569,12 +569,12 @@ def record.to_param() 1 end
       it "must return nil if persisted with changes" do
         record.persist!
         record[:uuid] = 'changed'
-        record.valid?.must_equal nil
+        record.valid?.must_be_nil
       end
 
       it "must return nil if not persisted with changes and no errors" do
         record[:uuid] = 'changed'
-        record.valid?.must_equal nil
+        record.valid?.must_be_nil
       end
 
       it "must return false if it has errors" do
diff --git a/spec/recurly_v2/subscription_spec.rb b/spec/recurly_v2/subscription_spec.rb
index 7ec9cdede..06dc8dcca 100644
--- a/spec/recurly_v2/subscription_spec.rb
+++ b/spec/recurly_v2/subscription_spec.rb
@@ -347,7 +347,7 @@
         stub_api_request :get, 'subscriptions/abcdef1234567890', 'subscriptions/show-200-noinvoice'
 
         subscription = Subscription.find 'abcdef1234567890'
-        subscription.invoice.must_equal nil
+        subscription.invoice.must_be_nil
       end
     end
   end
@@ -405,12 +405,12 @@
 
     it "should be able to pause and resume a subscription" do
       sub = RecurlyV2::Subscription.find('abcdef1234567890')
-      sub.paused_at.must_equal nil
+      sub.paused_at.must_be_nil
       sub.pause(1).must_equal true
       sub.paused_at.must_be_instance_of DateTime
       sub.remaining_pause_cycles.must_equal 1
       sub.resume.must_equal true
-      sub.remaining_pause_cycles.must_equal nil
+      sub.remaining_pause_cycles.must_be_nil
     end
   end
 
diff --git a/spec/recurly_v2/transaction_spec.rb b/spec/recurly_v2/transaction_spec.rb
index dea2a1bf1..19264af1b 100644
--- a/spec/recurly_v2/transaction_spec.rb
+++ b/spec/recurly_v2/transaction_spec.rb
@@ -62,7 +62,7 @@
       transaction = Transaction.find 'abcdef1234567890'
       transaction_from_dump = Marshal.load(Marshal.dump(transaction))
 
-      transaction.instance_variables.must_equal transaction_from_dump.instance_variables
+      transaction.instance_variables.sort.must_equal transaction_from_dump.instance_variables.sort
     end
 
     it 'must return the same values' do
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index f43ae66d2..59a7c01b4 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -6,6 +6,8 @@
 require 'cgi'
 require 'minitest/autorun'
 require 'minitest/spec'
+require 'minitest/global_expectations'
+require 'minitest/mock'
 require 'webmock'
 
 WebMock.enable!