diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 7f98f8e..9004672 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -6,10 +6,16 @@ on: [push, pull_request]
 jobs:
   test-ruby:
     runs-on: ${{ matrix.os }}-latest
+    continue-on-error: ${{ matrix.experimental || false }}
     strategy:
+      fail-fast: false
       matrix:
         os: [ubuntu]
-        ruby-version: ["2.6", "2.7", "3.0", "3.1", "3.2", "3.3", "3.4"]
+        ruby-version: ["2.6", "2.7", "3.0", "3.1", "3.2", "3.3", "3.4", "4.0"]
+        include:
+          - os: ubuntu
+            ruby-version: "head"
+            experimental: true
     steps:
       - uses: actions/checkout@v2
       - name: Setup Ruby ${{ matrix.ruby-version }}
diff --git a/Gemfile b/Gemfile
index 52aa166..6d1cc79 100644
--- a/Gemfile
+++ b/Gemfile
@@ -7,5 +7,5 @@ git_source(:github) { |repo_name| "https://github.com/#{repo_name}" }
 # Specify your gem's dependencies in skunk.gemspec
 gemspec
 
-gem "reek", "~> 6.1"
-gem "rubocop", "~> 1.48"
+gem "reek"
+gem "rubocop"
diff --git a/skunk.gemspec b/skunk.gemspec
index 0252525..eb37979 100644
--- a/skunk.gemspec
+++ b/skunk.gemspec
@@ -38,12 +38,12 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
+  spec.add_dependency "ostruct", "~> 0.6"
   spec.add_dependency "path_expander", "< 2.0"
   spec.add_dependency "rubycritic", ">= 4.5.2", "< 5.0"
   spec.add_dependency "terminal-table", "~> 3.0"
 
   spec.add_development_dependency "codecov", "~> 0.1.16"
-  spec.add_development_dependency "debug"
   spec.add_development_dependency "minitest", "< 6"
   spec.add_development_dependency "minitest-around", "~> 0.5.0"
   spec.add_development_dependency "minitest-stub_any_instance", "~> 1.0.2"
diff --git a/test/lib/skunk/cli/options/argv_test.rb b/test/lib/skunk/cli/options/argv_test.rb
index 20bfb45..987b93b 100644
--- a/test/lib/skunk/cli/options/argv_test.rb
+++ b/test/lib/skunk/cli/options/argv_test.rb
@@ -26,6 +26,10 @@
   end
 
   describe "#formats" do
+    before do
+      Skunk::Config.reset
+    end
+
     after do
       Skunk::Config.reset
     end
diff --git a/test/lib/skunk/config_test.rb b/test/lib/skunk/config_test.rb
index a04e1c6..e708eae 100644
--- a/test/lib/skunk/config_test.rb
+++ b/test/lib/skunk/config_test.rb
@@ -11,6 +11,12 @@ def setup
       Config.reset
     end
 
+    # Reset again after each test so the global singleton does not leak
+    # mutated formats into tests in other files (minitest randomizes order)
+    def teardown
+      Config.reset
+    end
+
     def test_default_format
       assert_equal [:console], Config.formats
     end