diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f4e0828..d4758d0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,18 +1,21 @@
 name: CI
 
-on: push
+on:
+  push:
+    branches: [master, main]
+  pull_request:
 
 jobs:
-  build:
+  test:
     runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false
       matrix:
-        ruby-version: ['2.7', '3.0', '3.1', '3.2']
+        ruby-version: ['3.3', '3.4', '4.0']
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
@@ -22,6 +25,35 @@ jobs:
 
     - name: Run tests
       run: bundle exec rspec
+      env:
+        COVERAGE: 'true'
 
-    - name: Run mutant
-      run: bundle exec mutant run
+  rubocop:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '4.0'
+        bundler-cache: true
+
+    - name: Run RuboCop
+      run: bundle exec rubocop
+
+  audit:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '4.0'
+        bundler-cache: true
+
+    - name: Run bundler-audit
+      run: bundle exec bundler-audit check --update
diff --git a/.pelusa.yml b/.pelusa.yml
deleted file mode 100644
index c5c35ef..0000000
--- a/.pelusa.yml
+++ /dev/null
@@ -1,9 +0,0 @@
-sources: lib/**/*.rb
-lints:
-  InstanceVariables:
-    limit: 1
-  LineRestriction:
-    limit: 87
-  ElseClauses:
-    exclude:
-      - 'IceNine::Freezer'
diff --git a/.rubocop.yml b/.rubocop.yml
index 9c91d1f..9d77ada 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -1,8 +1,93 @@
+plugins:
+  - rubocop-performance
+  - rubocop-rspec
+
 AllCops:
+  NewCops: enable
+  TargetRubyVersion: 3.3
+  SuggestExtensions: false
   Exclude:
-    - 'Gemfile'
-    - 'Gemfile.devtools'
     - 'benchmarks/**/*'
-    - 'ice_nine.gemspec'
     - 'vendor/**/*'
-    - 'Guardfile'
+
+# This codebase favours a very dense, "one class/module per concept" style
+# with lots of tiny classes (e.g. lib/ice_nine/freezer/*.rb), so the
+# class-level documentation cop is enough; per-file/module-length limits
+# below are relaxed to match that style rather than forcing artificial
+# splits.
+Style/Documentation:
+  Enabled: true
+
+Style/ClassAndModuleChildren:
+  Exclude:
+    - 'spec/**/*_spec.rb'
+
+Metrics/ClassLength:
+  Max: 100
+
+Metrics/ModuleLength:
+  Max: 100
+  Exclude:
+    - 'spec/**/*'
+
+Metrics/BlockLength:
+  Exclude:
+    - 'spec/**/*'
+    - 'ice_nine.gemspec'
+
+# The library re-opens IceNine::Freezer for each supported Ruby core class,
+# so short single-purpose subclasses are idiomatic here, not a smell.
+Style/EmptyMethod:
+  EnforcedStyle: expanded
+
+Layout/LineLength:
+  Max: 100
+
+RSpec/MultipleMemoizedHelpers:
+  Enabled: false
+
+RSpec/NestedGroups:
+  Max: 5
+
+RSpec/ExampleLength:
+  Enabled: false
+
+RSpec/MultipleExpectations:
+  Enabled: false
+
+# The suite consistently defines a single `subject` per example group and
+# references it explicitly for readability in multi-line expectations
+# instead of relying on the implicit `is_expected` syntax.
+RSpec/NamedSubject:
+  Enabled: false
+
+# These doubles stand in for arbitrary opaque objects that are only ever
+# identity-compared (`be(...)`); there is no real interface to verify them
+# against.
+RSpec/VerifiedDoubles:
+  Enabled: false
+
+# element_reader_spec.rb intentionally defines and removes real global
+# constants (Hash::Test, Application::User, Mash::State, ...) to exercise
+# IceNine::Freezer's name-based constant lookup across namespaces -- that is
+# the exact behaviour under test, not a leaky-state accident stub_const
+# would paper over.
+RSpec/RemoveConst:
+  Exclude:
+    - 'spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb'
+
+RSpec/LeakyConstantDeclaration:
+  Exclude:
+    - 'spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb'
+
+RSpec/BeforeAfterAll:
+  Exclude:
+    - 'spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb'
+
+Lint/ConstantDefinitionInBlock:
+  Exclude:
+    - 'spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb'
+
+Lint/EmptyClass:
+  Exclude:
+    - 'spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb'
diff --git a/.ruby-version b/.ruby-version
new file mode 100644
index 0000000..d13e837
--- /dev/null
+++ b/.ruby-version
@@ -0,0 +1 @@
+4.0.6
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 333b403..4a8550b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -7,5 +7,5 @@ Contributing
   * Follow this [style guide](https://github.com/dkubb/styleguide).
 * Add specs for it. This is important so I don't break it in a future version unintentionally. Tests must cover all branches within the code, and code must be fully covered.
 * Commit, do not mess with Rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
-* Run "rake ci". This must pass and not show any regressions in the metrics for the code to be merged.
+* Run `bundle exec rake`. This runs the spec suite (with 100% line/branch coverage enforced) and RuboCop, and must pass with no regressions for the code to be merged.
 * Send me a pull request. Bonus points for topic branches.
diff --git a/Gemfile b/Gemfile
index ea82bc2..b00b4c3 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,15 +1,23 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 source 'https://rubygems.org'
 
 gemspec
 
 group :development, :test do
-  gem 'rspec',        '~> 3.8', '>= 3.8.0'
-  gem 'mutant',       github: 'mbj/mutant'
-  gem 'mutant-rspec', github: 'mbj/mutant'
+  gem 'rake',  '~> 13.2'
+  gem 'rspec', '~> 3.13'
 
-  source 'https://oss:sxCL1o1navkPi2XnGB5WYBrhpY9iKIPL@gem.mutant.dev' do
-    gem 'mutant-license'
-  end
+  # No longer bundled with Ruby by default since 3.4; the numeric freezer
+  # specs exercise BigDecimal explicitly.
+  gem 'bigdecimal', '~> 3.1'
+
+  gem 'rubocop', '~> 1.75', require: false
+  gem 'rubocop-performance', '~> 1.24', require: false
+  gem 'rubocop-rspec', '~> 3.6', require: false
+
+  gem 'simplecov', '~> 0.22', require: false
+  gem 'yard',      '~> 0.9',  require: false
+
+  gem 'bundler-audit', '~> 0.9', require: false
 end
diff --git a/Gemfile.devtools b/Gemfile.devtools
deleted file mode 100644
index 09ebbfe..0000000
--- a/Gemfile.devtools
+++ /dev/null
@@ -1,72 +0,0 @@
-# encoding: utf-8
-
-group :development do
-  gem 'rake',       '~> 10.4.0'
-  gem 'rspec',      '~> 3.1.0'
-  gem 'rspec-core', '~> 3.1.7'
-  gem 'rspec-its',  '~> 1.1.0'
-  gem 'yard',       '~> 0.8.7.6'
-
-  platform :rbx do
-    gem 'rubysl-singleton', '~> 2.0.0'
-  end
-end
-
-group :yard do
-  gem 'kramdown', '~> 1.5.0'
-end
-
-group :guard do
-  gem 'guard',         '~> 2.10.1'
-  gem 'guard-bundler', '~> 2.0.0'
-  gem 'guard-rspec',   '~> 4.3.1'
-  gem 'guard-rubocop', '~> 1.2.0'
-
-  # file system change event handling
-  gem 'listen',     '~> 2.8.1'
-  gem 'rb-fchange', '~> 0.0.6', require: false
-  gem 'rb-fsevent', '~> 0.9.4', require: false
-  gem 'rb-inotify', '~> 0.9.5', require: false
-
-  # notification handling
-  gem 'libnotify',               '~> 0.8.4', require: false
-  gem 'rb-notifu',               '~> 0.0.4', require: false
-  gem 'terminal-notifier-guard', '~> 1.6.4', require: false
-end
-
-group :metrics do
-  gem 'coveralls', '~> 0.7.2'
-  gem 'flay',      '~> 2.5.0'
-  gem 'flog',      '~> 4.3.0'
-  gem 'reek',      '~> 1.5.0'
-  gem 'rubocop',   '~> 0.27.1'
-  gem 'simplecov', '~> 0.9.1'
-  gem 'yardstick', '~> 0.9.9'
-
-  platforms :mri do
-    gem 'mutant',       '~> 0.6.7', git: 'https://github.com/mbj/mutant.git'
-    gem 'mutant-rspec', '~> 0.6.7', git: 'https://github.com/mbj/mutant.git'
-  end
-
-  platforms :ruby_19, :ruby_20 do
-    gem 'yard-spellcheck', '~> 0.1.5'
-  end
-
-  platform :rbx do
-    gem 'json',               '~> 1.8.1'
-    gem 'racc',               '~> 1.4.12'
-    gem 'rubysl-logger',      '~> 2.1.0'
-    gem 'rubysl-open-uri',    '~> 2.0.0'
-    gem 'rubysl-prettyprint', '~> 2.0.3'
-  end
-end
-
-group :benchmarks do
-  gem 'rbench', '~> 0.2.3'
-end
-
-platform :jruby do
-  group :jruby do
-    gem 'jruby-openssl', '~> 0.9.4'
-  end
-end
diff --git a/Guardfile b/Guardfile
deleted file mode 100644
index 2218cb6..0000000
--- a/Guardfile
+++ /dev/null
@@ -1,24 +0,0 @@
-# encoding: utf-8
-
-guard :bundler do
-  watch('Gemfile')
-end
-
-# rubocop:disable LineLength
-guard :rspec, cli: File.read('.rspec').split.join(' '), keep_failed: false do
-  # run all specs if configuration is modified
-  watch('Guardfile')           { 'spec' }
-  watch('Gemfile.lock')        { 'spec' }
-  watch('spec/spec_helper.rb') { 'spec' }
-
-  # run all specs if supporting files files are modified
-  watch(%r{\Aspec/(?:lib|support|shared)/.+\.rb\z}) { 'spec' }
-
-  # run unit specs if associated lib code is modified
-  watch(/\Alib\/(.+)\.rb/)                                            { |m| Dir["spec/unit/#{m[1]}"]         }
-  watch(%r{\Alib/(.+)/support/(.+)\.rb\z})                            { |m| Dir["spec/unit/#{m[1]}/#{m[2]}"] }
-  watch("lib/#{File.basename(File.expand_path('../', __FILE__))}.rb") { 'spec'                               }
-
-  # run a spec if it is modified
-  watch(%r{\Aspec/(?:unit|integration)/.+_spec\.rb\z})
-end
diff --git a/README.md b/README.md
index 08e19c7..4a75ba2 100644
--- a/README.md
+++ b/README.md
@@ -5,15 +5,9 @@ Deep freeze ruby objects
 
 [![Gem Version](https://badge.fury.io/rb/ice_nine.svg)][gem]
 [![Build Status](https://github.com/dkubb/ice_nine/actions/workflows/ci.yml/badge.svg)][ci]
-[![Code Climate](https://codeclimate.com/github/dkubb/ice_nine.png)][codeclimate]
-[![Inline docs](http://inch-ci.org/github/dkubb/ice_nine.svg?branch=master)][inch]
 
 [gem]: https://rubygems.org/gems/ice_nine
 [ci]: https://github.com/dkubb/ice_nine/actions/
-[travis]: https://travis-ci.org/dkubb/ice_nine
-[gemnasium]: https://gemnasium.com/dkubb/ice_nine
-[codeclimate]: https://codeclimate.com/github/dkubb/ice_nine
-[inch]: http://inch-ci.org/github/dkubb/ice_nine
 
 Examples
 --------
@@ -40,6 +34,25 @@ object = Object.new
 object.deep_freeze
 ```
 
+Requirements
+------------
+
+ice_nine requires Ruby 3.3 or newer, and is tested against Ruby 3.3, 3.4
+and 4.0.
+
+Development
+-----------
+
+```shell
+bundle install
+bundle exec rake      # runs the spec suite and RuboCop
+bundle exec rspec     # spec suite only
+bundle exec rubocop   # lint only
+```
+
+Set `COVERAGE=true` when running the spec suite to generate a SimpleCov
+report under `coverage/`; the suite enforces 100% line and branch coverage.
+
 Contributing
 ------------
 
diff --git a/Rakefile b/Rakefile
index b4ca397..50845e9 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,15 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
-Rake.application.load_imports
+require 'bundler/gem_tasks'
+require 'rspec/core/rake_task'
+
+RSpec::Core::RakeTask.new(:spec)
+
+begin
+  require 'rubocop/rake_task'
+  RuboCop::RakeTask.new(:rubocop)
+rescue LoadError
+  nil
+end
+
+task default: %i[spec rubocop]
diff --git a/benchmarks/speed.rb b/benchmarks/speed.rb
index 2a00c32..d760962 100755
--- a/benchmarks/speed.rb
+++ b/benchmarks/speed.rb
@@ -1,16 +1,15 @@
 #!/usr/bin/env ruby
-
-# encoding: utf-8
+# frozen_string_literal: true
 
 # benchmark speed of deep freeze
 
-$LOAD_PATH.unshift File.expand_path('../../lib', __FILE__)
+$LOAD_PATH.unshift File.expand_path('../lib', __dir__)
 
-require 'rbench'
+require 'benchmark'
 require 'ice_nine'
 
 # @return [Hash]
-def self.nested(depth, width, array_length)
+def nested(depth, width, array_length)
   hash = {}
 
   1.upto(width) do |n|
@@ -18,17 +17,17 @@ def self.nested(depth, width, array_length)
   end
 
   unless depth == 1
-    hash[(width - 1).to_s] = array_length.times.map { nested(depth - 1, width, array_length) }
+    hash[(width - 1).to_s] = Array.new(array_length) { nested(depth - 1, width, array_length) }
     hash[width.to_s] = nested(depth - 1, width, array_length)
   end
 
   hash
 end
 
-hash = nested(3, 5, 500)
+hash  = nested(3, 5, 500)
 hash2 = nested(3, 5, 500)
 
-RBench.run do
-  report('deep_freeze')  { IceNine.deep_freeze(hash)   }
-  report('deep_freeze!') { IceNine.deep_freeze!(hash2) }
+Benchmark.bmbm do |x|
+  x.report('deep_freeze')  { IceNine.deep_freeze(hash)   }
+  x.report('deep_freeze!') { IceNine.deep_freeze!(hash2) }
 end
diff --git a/config/devtools.yml b/config/devtools.yml
deleted file mode 100644
index dbdc79a..0000000
--- a/config/devtools.yml
+++ /dev/null
@@ -1,2 +0,0 @@
----
-unit_test_timeout: 0.1
diff --git a/config/flay.yml b/config/flay.yml
deleted file mode 100644
index 50ae2d5..0000000
--- a/config/flay.yml
+++ /dev/null
@@ -1,3 +0,0 @@
----
-threshold: 8
-total_score: 52
diff --git a/config/flog.yml b/config/flog.yml
deleted file mode 100644
index aa98167..0000000
--- a/config/flog.yml
+++ /dev/null
@@ -1,2 +0,0 @@
----
-threshold: 5.5
diff --git a/config/mutant.yml b/config/mutant.yml
deleted file mode 100644
index 54be0c4..0000000
--- a/config/mutant.yml
+++ /dev/null
@@ -1,12 +0,0 @@
----
-integration:
-  name: rspec
-requires:
-  - ice_nine
-matcher:
-  subjects:
-    - IceNine*
-mutation:
-  timeout: 1.0
-coverage_criteria:
-  timeout: true
diff --git a/config/reek.yml b/config/reek.yml
deleted file mode 100644
index ef42f14..0000000
--- a/config/reek.yml
+++ /dev/null
@@ -1,105 +0,0 @@
----
-Attribute:
-  enabled: true
-  exclude: []
-BooleanParameter:
-  enabled: true
-  exclude: []
-ClassVariable:
-  enabled: true
-  exclude: []
-ControlParameter:
-  enabled: true
-  exclude: []
-DataClump:
-  enabled: true
-  exclude: []
-  max_copies: 2
-  min_clump_size: 2
-DuplicateMethodCall:
-  enabled: true
-  exclude: []
-  max_calls: 1
-  allow_calls: []
-FeatureEnvy:
-  enabled: true
-  exclude:
-  - IceNine::RecursionGuard::Frozen#guard
-IrresponsibleModule:
-  enabled: true
-  exclude: []
-LongParameterList:
-  enabled: true
-  exclude: []
-  max_params: 2
-  overrides:
-    initialize:
-      max_params: 3
-LongYieldList:
-  enabled: true
-  exclude: []
-  max_params: 2
-NestedIterators:
-  enabled: true
-  exclude: []
-  max_allowed_nesting: 1
-  ignore_iterators: []
-NilCheck:
-  enabled: true
-  exclude: []
-RepeatedConditional:
-  enabled: true
-  exclude: []
-  max_ifs: 1
-TooManyInstanceVariables:
-  enabled: true
-  exclude: []
-  max_instance_variables: 3
-TooManyMethods:
-  enabled: true
-  exclude: []
-  max_methods: 10
-TooManyStatements:
-  enabled: true
-  exclude:
-  - each
-  max_statements: 5
-UncommunicativeMethodName:
-  enabled: true
-  exclude: []
-  reject:
-  - !ruby/regexp /^[a-z]$/
-  - !ruby/regexp /[0-9]$/
-  - !ruby/regexp /[A-Z]/
-  accept: []
-UncommunicativeModuleName:
-  enabled: true
-  exclude: []
-  reject:
-  - !ruby/regexp /^.$/
-  - !ruby/regexp /[0-9]$/
-  accept: []
-UncommunicativeParameterName:
-  enabled: true
-  exclude: []
-  reject:
-  - !ruby/regexp /^.$/
-  - !ruby/regexp /[0-9]$/
-  - !ruby/regexp /[A-Z]/
-  accept: []
-UncommunicativeVariableName:
-  enabled: true
-  exclude: []
-  reject:
-  - !ruby/regexp /^.$/
-  - !ruby/regexp /[0-9]$/
-  - !ruby/regexp /[A-Z]/
-  accept: []
-UnusedParameters:
-  enabled: true
-  exclude: []
-UtilityFunction:
-  enabled: true
-  exclude:
-  - IceNine::RecursionGuard::Frozen#guard
-  max_helper_calls: 0
diff --git a/config/roodi.yml b/config/roodi.yml
deleted file mode 100644
index 242e8be..0000000
--- a/config/roodi.yml
+++ /dev/null
@@ -1,16 +0,0 @@
----
-AbcMetricMethodCheck:            { score: 1 }
-AssignmentInConditionalCheck:    { }
-CaseMissingElseCheck:            { }
-ClassLineCountCheck:             { line_count: 88 }
-ClassNameCheck:                  { pattern: !ruby/regexp '/\A(?:[A-Z]+|[A-Z][a-z](?:[A-Z]?[a-z])+)\z/' }
-ClassVariableCheck:              { }
-CyclomaticComplexityBlockCheck:  { complexity: 3 }
-CyclomaticComplexityMethodCheck: { complexity: 1 }
-EmptyRescueBodyCheck:            { }
-ForLoopCheck:                    { }
-MethodLineCountCheck:            { line_count: 1 }
-MethodNameCheck:                 { pattern: !ruby/regexp '/\A(?:[a-z\d](?:_?[a-z\d])+[?!=]?|\[\]=?|==|<=>|<<|[+*&|-])\z/' }
-ModuleLineCountCheck:            { line_count: 92 }
-ModuleNameCheck:                 { pattern: !ruby/regexp '/\A(?:[A-Z]+|[A-Z][a-z](?:[A-Z]?[a-z])+)\z/' }
-ParameterNumberCheck:            { parameter_count: 0 }
diff --git a/config/rubocop.yml b/config/rubocop.yml
deleted file mode 100644
index 18eeafd..0000000
--- a/config/rubocop.yml
+++ /dev/null
@@ -1,114 +0,0 @@
-inherit_from: ../.rubocop.yml
-
-# Avoid parameter lists longer than five parameters.
-ParameterLists:
-  Max: 3
-  CountKeywordArgs: true
-
-# Avoid more than `Max` levels of nesting.
-BlockNesting:
-  Max: 3
-
-# Align with the style guide.
-CollectionMethods:
-  PreferredMethods:
-    collect:  'map'
-    inject:   'reduce'
-    find:     'detect'
-    find_all: 'select'
-
-# Do not force public/protected/private keyword to be indented at the same
-# level as the def keyword. My personal preference is to outdent these keywords
-# because I think when scanning code it makes it easier to identify the
-# sections of code and visually separate them. When the keyword is at the same
-# level I think it sort of blends in with the def keywords and makes it harder
-# to scan the code and see where the sections are.
-AccessModifierIndentation:
-  Enabled: false
-
-# Limit line length
-LineLength:
-  Max: 79
-
-# Disable documentation checking until a class needs to be documented once
-Documentation:
-  Enabled: false
-
-# Do not always use &&/|| instead of and/or.
-AndOr:
-  Enabled: false
-
-# Do not favor modifier if/unless usage when you have a single-line body
-IfUnlessModifier:
-  Enabled: false
-
-# Allow case equality operator (in limited use within the specs)
-CaseEquality:
-  Enabled: false
-
-# Constants do not always have to use SCREAMING_SNAKE_CASE
-ConstantName:
-  Enabled: false
-
-# Not all trivial readers/writers can be defined with attr_* methods
-TrivialAccessors:
-  Enabled: false
-
-# Allow empty lines around class body
-EmptyLinesAroundClassBody:
-  Enabled: false
-
-# Allow empty lines around module body
-EmptyLinesAroundModuleBody:
-  Enabled: false
-
-# Allow multiple line operations to not require indentation
-MultilineOperationIndentation:
-  Enabled: false
-
-# Prefer String#% over Kernel#sprintf
-FormatString:
-  Enabled: false
-
-# Use square brackets for literal Array objects
-PercentLiteralDelimiters:
-  PreferredDelimiters:
-    '%':  ()
-    '%i': '[]'
-    '%q': ()
-    '%Q': ()
-    '%r': '{}'
-    '%s': ()
-    '%w': '[]'
-    '%W': '[]'
-    '%x': ()
-
-# Align if/else blocks with the variable assignment
-EndAlignment:
-  AlignWith: variable
-
-# Do not always align parameters when it is easier to read
-AlignParameters:
-  Exclude:
-    - spec/**/*_spec.rb
-
-# Prefer #kind_of? over #is_a?
-ClassCheck:
-  EnforcedStyle: kind_of?
-
-# Do not prefer double quotes to be used when %q or %Q is more appropriate
-UnneededPercentQ:
-  Enabled: false
-
-# Allow a maximum ABC score
-Metrics/AbcSize:
-  Max: 6.08
-
-# Allow modules to be qualified with a "::" prefix
-ClassAndModuleChildren:
-  Exclude:
-    - spec/**/*_spec.rb
-
-# Allow additional spaces
-ExtraSpacing:
-  Enabled: false
diff --git a/config/yardstick.yml b/config/yardstick.yml
deleted file mode 100644
index a6b63e8..0000000
--- a/config/yardstick.yml
+++ /dev/null
@@ -1,2 +0,0 @@
----
-threshold: 100
diff --git a/ice_nine.gemspec b/ice_nine.gemspec
index fcb0c57..8a9bcfe 100644
--- a/ice_nine.gemspec
+++ b/ice_nine.gemspec
@@ -1,6 +1,7 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
-require File.expand_path('../lib/ice_nine/version', __FILE__)
+require 'English'
+require_relative 'lib/ice_nine/version'
 
 Gem::Specification.new do |gem|
   gem.name        = 'ice_nine'
@@ -13,12 +14,13 @@ Gem::Specification.new do |gem|
   gem.license     = 'MIT'
 
   gem.require_paths    = %w[lib]
-  gem.files            = `git ls-files`.split($/)
-  gem.test_files       = `git ls-files -- spec/{unit,integration}`.split($/)
+  gem.files            = `git ls-files -- lib LICENSE README.md TODO`.split($INPUT_RECORD_SEPARATOR)
   gem.extra_rdoc_files = %w[LICENSE README.md TODO]
 
-  gem.required_ruby_version = '>= 2.7.3'
+  gem.required_ruby_version = '>= 3.3'
 
-  gem.add_development_dependency('bundler', '~> 2.2',  '>= 2.2.33')
-  gem.add_development_dependency('rake',    '~> 13.0', '>= 13.0.6')
+  gem.metadata['rubygems_mfa_required'] = 'true'
+  gem.metadata['changelog_uri']         = "#{gem.homepage}/blob/master/README.md"
+  gem.metadata['source_code_uri']       = gem.homepage
+  gem.metadata['bug_tracker_uri']       = "#{gem.homepage}/issues"
 end
diff --git a/lib/ice_nine.rb b/lib/ice_nine.rb
index a659785..72a5f8b 100644
--- a/lib/ice_nine.rb
+++ b/lib/ice_nine.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'ice_nine/support/recursion_guard'
 
@@ -20,7 +20,6 @@
 
 # Base IceNine module
 module IceNine
-
   # Deep Freeze an object
   #
   # @example
@@ -55,5 +54,4 @@ def self.deep_freeze(object)
   def self.deep_freeze!(object)
     Freezer.deep_freeze!(object)
   end
-
-end # IceNine
+end
diff --git a/lib/ice_nine/core_ext/object.rb b/lib/ice_nine/core_ext/object.rb
index 7e541fd..1ff5b7e 100644
--- a/lib/ice_nine/core_ext/object.rb
+++ b/lib/ice_nine/core_ext/object.rb
@@ -1,13 +1,10 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
-
   # Core Ruby extensions
   module CoreExt
-
     # Extend Object with deep freezing
     module Object
-
       # Deep freeze an object
       #
       # @example
@@ -33,10 +30,9 @@ def deep_freeze
       def deep_freeze!
         IceNine.deep_freeze!(self)
       end
-
-    end # Object
-  end # CoreExt
-end # IceNine
+    end
+  end
+end
 
 # Add Object#deep_freeze
 Object.instance_eval { include IceNine::CoreExt::Object }
diff --git a/lib/ice_nine/freezer.rb b/lib/ice_nine/freezer.rb
index 035e928..80aeb99 100644
--- a/lib/ice_nine/freezer.rb
+++ b/lib/ice_nine/freezer.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
-
   # The default class that handles freezing objects
   class Freezer
-
     # Cache the Freezer classes returned for each type
     @freezer_cache = Hash.new do |cache, mod|
       freezer = nil
@@ -68,7 +66,7 @@ def self.find(name)
       freezer = name.split('::').reduce(self) do |mod, const|
         mod.const_lookup(const) or break mod
       end
-      freezer if freezer < self  # only return a descendant freezer
+      freezer if freezer < self # only return a descendant freezer
     end
 
     private_class_method :find
@@ -104,6 +102,5 @@ def self.guarded_deep_freeze(object, recursion_guard)
     class << self
       protected :const_lookup, :guarded_deep_freeze
     end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/array.rb b/lib/ice_nine/freezer/array.rb
index e8d7d16..c155fb5 100644
--- a/lib/ice_nine/freezer/array.rb
+++ b/lib/ice_nine/freezer/array.rb
@@ -1,11 +1,9 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # A freezer class for handling Array objects
     class Array < Object
-
       # Deep Freeze an Array
       #
       # @example
@@ -22,7 +20,6 @@ def self.guarded_deep_freeze(array, recursion_guard)
           Freezer.guarded_deep_freeze(entry, recursion_guard)
         end
       end
-
-    end # Array
-  end # Freezer
-end # IceNine
+    end
+  end
+end
diff --git a/lib/ice_nine/freezer/false_class.rb b/lib/ice_nine/freezer/false_class.rb
index f5774db..ff64daa 100644
--- a/lib/ice_nine/freezer/false_class.rb
+++ b/lib/ice_nine/freezer/false_class.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # Skip freezing false objects
     class FalseClass < NoFreeze; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/hash.rb b/lib/ice_nine/freezer/hash.rb
index d180284..ce5e126 100644
--- a/lib/ice_nine/freezer/hash.rb
+++ b/lib/ice_nine/freezer/hash.rb
@@ -1,11 +1,9 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # A freezer class for handling Hash objects
     class Hash < Object
-
       # Deep Freeze a Hash
       #
       # @example
@@ -40,7 +38,6 @@ def self.freeze_key_value_pairs(hash, recursion_guard)
       end
 
       private_class_method :freeze_key_value_pairs
-
-    end # Hash
-  end # Freezer
-end # IceNine
+    end
+  end
+end
diff --git a/lib/ice_nine/freezer/module.rb b/lib/ice_nine/freezer/module.rb
index 2674f5f..4969f8f 100644
--- a/lib/ice_nine/freezer/module.rb
+++ b/lib/ice_nine/freezer/module.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # Skip freezing Module objects
     class Module < NoFreeze; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/nil_class.rb b/lib/ice_nine/freezer/nil_class.rb
index d95f442..29550b8 100644
--- a/lib/ice_nine/freezer/nil_class.rb
+++ b/lib/ice_nine/freezer/nil_class.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # Skip freezing nil objects
     class NilClass < NoFreeze; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/no_freeze.rb b/lib/ice_nine/freezer/no_freeze.rb
index cfc8b79..4af6108 100644
--- a/lib/ice_nine/freezer/no_freeze.rb
+++ b/lib/ice_nine/freezer/no_freeze.rb
@@ -1,11 +1,9 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # A freezer class that does not freeze anything
     class NoFreeze < self
-
       # Pass through the object without freezing it
       #
       # @example
@@ -19,7 +17,6 @@ class NoFreeze < self
       def self.guarded_deep_freeze(object, _recursion_guard)
         object
       end
-
-    end # NoFreeze
-  end # Freezer
-end # IceNine
+    end
+  end
+end
diff --git a/lib/ice_nine/freezer/numeric.rb b/lib/ice_nine/freezer/numeric.rb
index f5dbdac..efad1a8 100644
--- a/lib/ice_nine/freezer/numeric.rb
+++ b/lib/ice_nine/freezer/numeric.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # Skip freezing Numeric objects
     class Numeric < NoFreeze; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/object.rb b/lib/ice_nine/freezer/object.rb
index 2e4a5b7..3d961ac 100644
--- a/lib/ice_nine/freezer/object.rb
+++ b/lib/ice_nine/freezer/object.rb
@@ -1,11 +1,9 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # A freezer class for handling Object instances
     class Object < self
-
       # Deep Freeze an object
       #
       # @example
@@ -41,9 +39,11 @@ def self.freeze_instance_variables(object, recursion_guard)
       end
 
       private_class_method :freeze_instance_variables
+    end
 
-    end # Object
-
+    # Freeze BasicObject instances using the same strategy as Object
+    #
+    # @api private
     BasicObject = Object
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/struct.rb b/lib/ice_nine/freezer/struct.rb
index a40c4b4..e0bc3e4 100644
--- a/lib/ice_nine/freezer/struct.rb
+++ b/lib/ice_nine/freezer/struct.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # A freezer class for handling Struct objects
     class Struct < Array; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/symbol.rb b/lib/ice_nine/freezer/symbol.rb
index 2dadc7e..37c5ec7 100644
--- a/lib/ice_nine/freezer/symbol.rb
+++ b/lib/ice_nine/freezer/symbol.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # Skip freezing Symbol objects
     class Symbol < NoFreeze; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/freezer/true_class.rb b/lib/ice_nine/freezer/true_class.rb
index e612d0c..ad2dfce 100644
--- a/lib/ice_nine/freezer/true_class.rb
+++ b/lib/ice_nine/freezer/true_class.rb
@@ -1,10 +1,8 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
   class Freezer
-
     # Skip freezing true objects
     class TrueClass < NoFreeze; end
-
-  end # Freezer
-end # IceNine
+  end
+end
diff --git a/lib/ice_nine/support/recursion_guard.rb b/lib/ice_nine/support/recursion_guard.rb
index 3d71da9..d14fa5b 100644
--- a/lib/ice_nine/support/recursion_guard.rb
+++ b/lib/ice_nine/support/recursion_guard.rb
@@ -1,20 +1,18 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
-
   # Protect against infinite recursion
   #
   # @private
   class RecursionGuard
-
     # Protects against infinite recursion by never yielding with the same
     # object more than once.
     class ObjectSet < self
-
       # Initialize a recursion guard
       #
       # @return [undefined]
       def initialize
+        super
         @object_ids = {}
       end
 
@@ -32,15 +30,14 @@ def initialize
       def guard(object)
         caller_object_id = object.__id__
         return object if @object_ids.key?(caller_object_id)
+
         @object_ids[caller_object_id] = nil
         yield
       end
-
-    end # ObjectSet
+    end
 
     # Protects against infinite recursion by not yielding with frozen objects
     class Frozen < self
-
       # Guard against recursively calling a block with the same frozen object
       #
       # @param [Object] object
@@ -48,10 +45,9 @@ class Frozen < self
       # @return [Object]
       def guard(object)
         return object if object.frozen?
+
         yield
       end
-
-    end # Frozen
-
-  end # RecursionGuard
-end # IceNine
+    end
+  end
+end
diff --git a/lib/ice_nine/version.rb b/lib/ice_nine/version.rb
index 02afb43..000f21a 100644
--- a/lib/ice_nine/version.rb
+++ b/lib/ice_nine/version.rb
@@ -1,8 +1,6 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 module IceNine
-
   # Gem version
-  VERSION = '0.11.2'.freeze
-
-end # IceNine
+  VERSION = '0.11.2'
+end
diff --git a/spec/integration/ice_nine/class_methods/deep_freeze_bang_spec.rb b/spec/integration/ice_nine/class_methods/deep_freeze_bang_spec.rb
index a7fc922..cc1ceb0 100644
--- a/spec/integration/ice_nine/class_methods/deep_freeze_bang_spec.rb
+++ b/spec/integration/ice_nine/class_methods/deep_freeze_bang_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -7,15 +7,15 @@
 describe IceNine, '.deep_freeze!' do
   subject { object.deep_freeze!(value) }
 
-  let(:object) { IceNine }
+  let(:object) { described_class }
 
   context 'with a shallowly frozen value' do
-    let(:value) { %w[a b].freeze }
+    let(:value) { [+'a', +'b'].freeze }
 
     it 'does not deep freeze' do
       expect(subject.select(&:frozen?)).to be_empty
     end
   end
 
-  it_should_behave_like 'IceNine.deep_freeze'
+  it_behaves_like 'IceNine.deep_freeze'
 end
diff --git a/spec/integration/ice_nine/class_methods/deep_freeze_spec.rb b/spec/integration/ice_nine/class_methods/deep_freeze_spec.rb
index 479339d..a5f778c 100644
--- a/spec/integration/ice_nine/class_methods/deep_freeze_spec.rb
+++ b/spec/integration/ice_nine/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -7,7 +7,7 @@
 describe IceNine, '.deep_freeze' do
   subject { object.deep_freeze(value) }
 
-  let(:object) { IceNine }
+  let(:object) { described_class }
 
   context 'with a shallowly frozen value' do
     let(:value) { ['a', %w[b c]].freeze }
@@ -17,5 +17,5 @@
     end
   end
 
-  it_should_behave_like 'IceNine.deep_freeze'
+  it_behaves_like 'IceNine.deep_freeze'
 end
diff --git a/spec/shared/array_deep_freeze.rb b/spec/shared/array_deep_freeze.rb
index b93b0d0..4bbd438 100644
--- a/spec/shared/array_deep_freeze.rb
+++ b/spec/shared/array_deep_freeze.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 shared_examples 'IceNine::Freezer::Array.deep_freeze' do
   it_behaves_like 'IceNine::Freezer::Object.deep_freeze'
diff --git a/spec/shared/hash_deep_freeze.rb b/spec/shared/hash_deep_freeze.rb
index e1b84ed..3422882 100644
--- a/spec/shared/hash_deep_freeze.rb
+++ b/spec/shared/hash_deep_freeze.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 shared_examples 'IceNine::Freezer::Hash.deep_freeze' do
   it_behaves_like 'IceNine::Freezer::Object.deep_freeze'
@@ -13,11 +13,11 @@
 
   if RUBY_VERSION >= '1.9' && RUBY_ENGINE == 'rbx'
     it 'does not freeze the state' do
-      expect(subject.instance_variable_get(:@state)).to_not be_frozen
+      expect(subject.instance_variable_get(:@state)).not_to be_frozen
     end
 
     it 'does not freeze the entries' do
-      expect(subject.instance_variable_get(:@entries)).to_not be_frozen
+      expect(subject.instance_variable_get(:@entries)).not_to be_frozen
     end
   end
 end
diff --git a/spec/shared/ice_nine_deep_freeze.rb b/spec/shared/ice_nine_deep_freeze.rb
index 3957b95..6f7fc15 100644
--- a/spec/shared/ice_nine_deep_freeze.rb
+++ b/spec/shared/ice_nine_deep_freeze.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 shared_examples 'IceNine.deep_freeze' do
   context 'with an Object' do
@@ -9,7 +9,7 @@
     end
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'freezes the object' do
@@ -26,7 +26,7 @@
       end
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'freezes the object' do
@@ -43,7 +43,7 @@
     let(:value) { %w[a] }
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'freezes the object' do
@@ -60,7 +60,7 @@
       end
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'freezes the object' do
@@ -77,7 +77,7 @@
     let(:value) { { Object.new => Object.new } }
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'freezes the object' do
@@ -98,7 +98,7 @@
       end
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'freezes the object' do
@@ -116,14 +116,14 @@
   end
 
   context 'with a String' do
-    let(:value) { '' }
+    let(:value) { +'' }
 
     before do
       value.instance_eval { @a = '1' }
     end
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'freezes the object' do
@@ -140,7 +140,7 @@
       end
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'freezes the object' do
@@ -154,11 +154,11 @@
   end
 
   context 'with a Struct' do
-    let(:value) { klass.new(%w[ 1 2 ]) }
-    let(:klass) { Struct.new(:a)       }
+    let(:value) { klass.new(%w[1 2]) }
+    let(:klass) { Struct.new(:a) }
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'freezes the object' do
@@ -175,7 +175,7 @@
       end
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'freezes the object' do
@@ -196,7 +196,7 @@
     end
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'freezes the object' do
@@ -213,7 +213,7 @@
       end
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'freezes the object' do
@@ -231,11 +231,11 @@
       let(:value) { value }
 
       it 'returns the object' do
-        should be(value)
+        expect(subject).to be(value)
       end
 
       it 'does not freeze the object' do
-        expect { subject }.to_not change(value, :frozen?).from(value.frozen?)
+        expect { subject }.not_to change(value, :frozen?).from(value.frozen?)
       end
     end
   end
diff --git a/spec/shared/no_freeze_deep_freeze.rb b/spec/shared/no_freeze_deep_freeze.rb
index 24b8fcf..8383c51 100644
--- a/spec/shared/no_freeze_deep_freeze.rb
+++ b/spec/shared/no_freeze_deep_freeze.rb
@@ -1,21 +1,21 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 shared_examples 'IceNine::Freezer::NoFreeze.deep_freeze' do
   before do
-    value.instance_eval { @a = '1' } unless value.frozen?
+    value.instance_eval { @a = +'1' } unless value.frozen?
   end
 
   it 'returns the object' do
-    should be(value)
+    expect(subject).to be(value)
   end
 
   it 'does not freeze the object' do
-    expect { subject }.to_not change(value, :frozen?).from(value.frozen?)
+    expect { subject }.not_to change(value, :frozen?).from(value.frozen?)
   end
 
   it 'does not freeze instance variables' do
     if subject.instance_variable_defined?(:@a)
-      expect(subject.instance_variable_get(:@a)).to_not be_frozen
+      expect(subject.instance_variable_get(:@a)).not_to be_frozen
     end
   end
 end
diff --git a/spec/shared/object_deep_freeze.rb b/spec/shared/object_deep_freeze.rb
index 1fe4d9f..9a54ea5 100644
--- a/spec/shared/object_deep_freeze.rb
+++ b/spec/shared/object_deep_freeze.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 shared_examples 'IceNine::Freezer::Object.deep_freeze' do
   before do
@@ -6,7 +6,7 @@
   end
 
   it 'returns the object' do
-    should be(value)
+    expect(subject).to be(value)
   end
 
   it 'freezes the object' do
diff --git a/spec/shared/range_deep_freeze.rb b/spec/shared/range_deep_freeze.rb
index feb19f9..a7e6ffa 100644
--- a/spec/shared/range_deep_freeze.rb
+++ b/spec/shared/range_deep_freeze.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 shared_examples 'IceNine::Freezer::Range.deep_freeze' do
   it_behaves_like 'IceNine::Freezer::Object.deep_freeze'
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 1329542..ebe0f87 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,26 +1,25 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 if ENV['COVERAGE'] == 'true'
   require 'simplecov'
 
-  SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
-    SimpleCov::Formatter::HTMLFormatter,
-  ]
+  SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter.new(
+    [SimpleCov::Formatter::HTMLFormatter]
+  )
 
   SimpleCov.start do
     command_name 'spec:unit'
+    enable_coverage :branch
 
-    add_filter 'config'
     add_filter 'spec'
-    add_filter 'vendor'
 
-    minimum_coverage 100
+    minimum_coverage line: 100, branch: 100
   end
 end
 
 require 'ice_nine'
 
-Dir[Pathname(__dir__).join('shared/**/*.rb')].each(&Kernel.method(:require))
+Dir[Pathname(__dir__).join('shared/**/*.rb')].each { |file| require file }
 
 RSpec.configure do |config|
   config.expect_with :rspec do |expect_with|
diff --git a/spec/support/config_alias.rb b/spec/support/config_alias.rb
deleted file mode 100644
index 9c3f42f..0000000
--- a/spec/support/config_alias.rb
+++ /dev/null
@@ -1,5 +0,0 @@
-# encoding: utf-8
-
-require 'rbconfig'
-
-::Config = RbConfig unless defined?(::Config)
diff --git a/spec/unit/ice_nine/class_methods/deep_freeze_bang_spec.rb b/spec/unit/ice_nine/class_methods/deep_freeze_bang_spec.rb
index a9f75b9..e92762a 100644
--- a/spec/unit/ice_nine/class_methods/deep_freeze_bang_spec.rb
+++ b/spec/unit/ice_nine/class_methods/deep_freeze_bang_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -6,7 +6,7 @@
 describe IceNine, '.deep_freeze!' do
   subject { object.deep_freeze!(value) }
 
-  let(:object) { IceNine    }
+  let(:object) { described_class }
   let(:value)  { Object.new }
 
   context 'when the object is not frozen' do
@@ -15,7 +15,7 @@
 
   context 'when the object is frozen' do
     before do
-      value.instance_eval { @a = '1' }
+      value.instance_eval { @a = +'1' }
       value.freeze
     end
 
diff --git a/spec/unit/ice_nine/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/class_methods/deep_freeze_spec.rb
index a811fa8..dbf2c0a 100644
--- a/spec/unit/ice_nine/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -6,7 +6,7 @@
 describe IceNine, '.deep_freeze' do
   subject { object.deep_freeze(value) }
 
-  let(:object) { IceNine    }
+  let(:object) { described_class }
   let(:value)  { Object.new }
 
   context 'when the object is not frozen' do
@@ -20,7 +20,7 @@
     end
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'leaves the object frozen' do
diff --git a/spec/unit/ice_nine/core_ext/object/deep_freeze_bang_spec.rb b/spec/unit/ice_nine/core_ext/object/deep_freeze_bang_spec.rb
index e14c356..5e05fab 100644
--- a/spec/unit/ice_nine/core_ext/object/deep_freeze_bang_spec.rb
+++ b/spec/unit/ice_nine/core_ext/object/deep_freeze_bang_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -7,7 +7,7 @@
 describe IceNine::CoreExt::Object, '#deep_freeze!' do
   subject { value.deep_freeze! }
 
-  let(:value) { Object.new.extend(IceNine::CoreExt::Object) }
+  let(:value) { Object.new.extend(described_class) }
 
   context 'when the object is not frozen' do
     it_behaves_like 'IceNine::Freezer::Object.deep_freeze'
@@ -15,7 +15,7 @@
 
   context 'when the object is frozen' do
     before do
-      value.instance_eval { @a = '1' }
+      value.instance_eval { @a = +'1' }
       value.freeze
     end
 
diff --git a/spec/unit/ice_nine/core_ext/object/deep_freeze_spec.rb b/spec/unit/ice_nine/core_ext/object/deep_freeze_spec.rb
index 3b6a57c..00739c1 100644
--- a/spec/unit/ice_nine/core_ext/object/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/core_ext/object/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -7,7 +7,7 @@
 describe IceNine::CoreExt::Object, '#deep_freeze' do
   subject { value.deep_freeze }
 
-  let(:value) { Object.new.extend(IceNine::CoreExt::Object) }
+  let(:value) { Object.new.extend(described_class) }
 
   it_behaves_like 'IceNine::Freezer::Object.deep_freeze'
 end
diff --git a/spec/unit/ice_nine/freezer/array/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/array/class_methods/deep_freeze_spec.rb
index 62df85b..d0906e8 100644
--- a/spec/unit/ice_nine/freezer/array/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/array/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
diff --git a/spec/unit/ice_nine/freezer/class_methods/deep_freeze_bang_spec.rb b/spec/unit/ice_nine/freezer/class_methods/deep_freeze_bang_spec.rb
index 450d467..45fefab 100644
--- a/spec/unit/ice_nine/freezer/class_methods/deep_freeze_bang_spec.rb
+++ b/spec/unit/ice_nine/freezer/class_methods/deep_freeze_bang_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -6,7 +6,7 @@
 describe IceNine::Freezer, '.deep_freeze!' do
   subject { object.deep_freeze!(value) }
 
-  let(:object) { IceNine::Freezer }
+  let(:object) { described_class }
   let(:value)  { Object.new       }
 
   context 'when the object is not frozen' do
@@ -15,7 +15,7 @@
 
   context 'when the object is frozen' do
     before do
-      value.instance_eval { @a = '1' }
+      value.instance_eval { @a = +'1' }
       value.freeze
     end
 
diff --git a/spec/unit/ice_nine/freezer/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/class_methods/deep_freeze_spec.rb
index e64b939..8bec2e3 100644
--- a/spec/unit/ice_nine/freezer/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -6,7 +6,7 @@
 describe IceNine::Freezer, '.deep_freeze' do
   subject { object.deep_freeze(value) }
 
-  let(:object) { IceNine::Freezer }
+  let(:object) { described_class }
   let(:value)  { Object.new       }
 
   context 'when the object is not frozen' do
@@ -20,7 +20,7 @@
     end
 
     it 'returns the object' do
-      should be(value)
+      expect(subject).to be(value)
     end
 
     it 'leaves the object frozen' do
diff --git a/spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb b/spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb
index cb67562..f0f9690 100644
--- a/spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb
+++ b/spec/unit/ice_nine/freezer/class_methods/element_reader_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
@@ -25,7 +25,7 @@
     end
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 
@@ -41,7 +41,7 @@ class User; end
     end
 
     after :all do
-      ::Application.send(:remove_const, :User)
+      Application.send(:remove_const, :User)
       Object.send(:remove_const, :Application)
     end
 
@@ -56,7 +56,7 @@ class User; end
     end
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 
@@ -65,7 +65,7 @@ class User; end
     let(:freezer) { IceNine::Freezer::Struct }
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 
@@ -73,7 +73,7 @@ class User; end
     let(:mod) { Object }
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 
@@ -81,7 +81,7 @@ class User; end
     let(:mod) { Class.new }
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 
@@ -89,7 +89,7 @@ class User; end
     let(:mod) { Module.new }
 
     it 'returns the freezer' do
-      should be_nil
+      expect(subject).to be_nil
     end
   end
 
@@ -104,7 +104,7 @@ class Hash::Test; end
     end
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 
@@ -119,7 +119,7 @@ class State; end
     end
 
     after :all do
-      ::Mash.send(:remove_const, :State)
+      Mash.send(:remove_const, :State)
       Object.send(:remove_const, :Mash)
     end
 
@@ -132,7 +132,7 @@ class State; end
     end
 
     it 'returns the freezer' do
-      should be(freezer)
+      expect(subject).to be(freezer)
     end
   end
 end
diff --git a/spec/unit/ice_nine/freezer/false_class/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/false_class/class_methods/deep_freeze_spec.rb
index 0424682..68f9d5d 100644
--- a/spec/unit/ice_nine/freezer/false_class/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/false_class/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
diff --git a/spec/unit/ice_nine/freezer/hash/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/hash/class_methods/deep_freeze_spec.rb
index 4a89ce5..09e04c8 100644
--- a/spec/unit/ice_nine/freezer/hash/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/hash/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
@@ -10,6 +10,7 @@
 
   context 'with a Hash object having a default proc' do
     let(:value) do
+      # rubocop:disable-next Lint/EmptyBlock -- only the Proc's frozen state is under test
       Hash.new {}.update(Object.new => Object.new)
     end
 
@@ -22,7 +23,7 @@
 
   context 'with a Hash object having a default value' do
     let(:value) do
-      Hash.new('').update(Object.new => Object.new)
+      Hash.new(+'').update(Object.new => Object.new)
     end
 
     it_behaves_like 'IceNine::Freezer::Hash.deep_freeze'
@@ -31,7 +32,7 @@
       expect(subject.default).to be_frozen
     end
 
-    context 'that is a circular reference' do
+    context 'with a default value that is a circular reference' do
       before { value.default = value }
 
       it_behaves_like 'IceNine::Freezer::Hash.deep_freeze'
diff --git a/spec/unit/ice_nine/freezer/module/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/module/class_methods/deep_freeze_spec.rb
index 0a316a5..052a99c 100644
--- a/spec/unit/ice_nine/freezer/module/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/module/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
diff --git a/spec/unit/ice_nine/freezer/nil_class/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/nil_class/class_methods/deep_freeze_spec.rb
index 6eff10f..2189b84 100644
--- a/spec/unit/ice_nine/freezer/nil_class/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/nil_class/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
diff --git a/spec/unit/ice_nine/freezer/no_freeze/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/no_freeze/class_methods/deep_freeze_spec.rb
index c749926..67dd355 100644
--- a/spec/unit/ice_nine/freezer/no_freeze/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/no_freeze/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer/no_freeze'
diff --git a/spec/unit/ice_nine/freezer/numeric/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/numeric/class_methods/deep_freeze_spec.rb
index 32b407b..cec123a 100644
--- a/spec/unit/ice_nine/freezer/numeric/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/numeric/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
diff --git a/spec/unit/ice_nine/freezer/object/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/object/class_methods/deep_freeze_spec.rb
index 31b72d4..15e6e69 100644
--- a/spec/unit/ice_nine/freezer/object/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/object/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
diff --git a/spec/unit/ice_nine/freezer/struct/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/struct/class_methods/deep_freeze_spec.rb
index cd1eeae..420f85b 100644
--- a/spec/unit/ice_nine/freezer/struct/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/struct/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'
diff --git a/spec/unit/ice_nine/freezer/symbol/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/symbol/class_methods/deep_freeze_spec.rb
index 1ac38c4..efbc863 100644
--- a/spec/unit/ice_nine/freezer/symbol/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/symbol/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
diff --git a/spec/unit/ice_nine/freezer/true_class/class_methods/deep_freeze_spec.rb b/spec/unit/ice_nine/freezer/true_class/class_methods/deep_freeze_spec.rb
index 39b27a0..3461ecd 100644
--- a/spec/unit/ice_nine/freezer/true_class/class_methods/deep_freeze_spec.rb
+++ b/spec/unit/ice_nine/freezer/true_class/class_methods/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/freezer'
diff --git a/spec/unit/ice_nine/recursion_guard/frozen/guard_spec.rb b/spec/unit/ice_nine/recursion_guard/frozen/guard_spec.rb
index a856a34..683d93e 100644
--- a/spec/unit/ice_nine/recursion_guard/frozen/guard_spec.rb
+++ b/spec/unit/ice_nine/recursion_guard/frozen/guard_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/support/recursion_guard'
@@ -6,13 +6,13 @@
 describe IceNine::RecursionGuard::Frozen, '#guard' do
   subject { object.guard(object_arg) { return_value } }
 
-  let(:object)       { IceNine::RecursionGuard::Frozen.new }
+  let(:object)       { described_class.new }
   let(:object_arg)   { Object.new                          }
   let(:return_value) { double('return_value')              }
 
   context 'when the object_arg is not frozen' do
     it 'returns the expected value' do
-      should be(return_value)
+      expect(subject).to be(return_value)
     end
   end
 
@@ -22,7 +22,7 @@
     end
 
     it 'returns the expected value' do
-      should be(object_arg)
+      expect(subject).to be(object_arg)
     end
   end
 end
diff --git a/spec/unit/ice_nine/recursion_guard/object_set/guard_spec.rb b/spec/unit/ice_nine/recursion_guard/object_set/guard_spec.rb
index f899c7e..9a12af2 100644
--- a/spec/unit/ice_nine/recursion_guard/object_set/guard_spec.rb
+++ b/spec/unit/ice_nine/recursion_guard/object_set/guard_spec.rb
@@ -1,39 +1,39 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine/support/recursion_guard'
 
 describe IceNine::RecursionGuard::ObjectSet, '#guard' do
-  let(:object)       { IceNine::RecursionGuard::ObjectSet.new }
-  let(:object_arg1)  { 'similar_but_not_equal_id'             }
-  let(:object_arg2)  { 'similar_but_not_equal_id'             }
-  let(:return_value) { double('return_value')                 }
+  let(:object) { described_class.new }
+  let(:first_object_arg) { +'similar_but_not_equal_id' }
+  let(:second_object_arg) { +'similar_but_not_equal_id' }
+  let(:return_value) { double('return_value') }
 
   context 'when the block is not recursive' do
     subject do
-      object.guard(object_arg1) { return_value }
-      object.guard(object_arg2) { return_value }
+      object.guard(first_object_arg) { return_value }
+      object.guard(second_object_arg) { return_value }
     end
 
     it 'returns the expected value' do
-      should be(return_value)
+      expect(subject).to be(return_value)
     end
   end
 
   context 'when the block is recursive' do
     subject do
-      object.guard(object_arg1) do
-        object.guard(object_arg2) do
-          expect(subject).to be(object_arg1)
+      object.guard(first_object_arg) do
+        object.guard(second_object_arg) do
+          expect(subject).to be(first_object_arg)
           return_value
         end
-        expect(subject).to be(object_arg1)
+        expect(subject).to be(first_object_arg)
         return_value
       end
     end
 
     it 'returns the expected value' do
-      should be(return_value)
+      expect(subject).to be(return_value)
     end
   end
 end
diff --git a/spec/unit/object/deep_freeze_spec.rb b/spec/unit/object/deep_freeze_spec.rb
index 4368b78..93448cb 100644
--- a/spec/unit/object/deep_freeze_spec.rb
+++ b/spec/unit/object/deep_freeze_spec.rb
@@ -1,4 +1,4 @@
-# encoding: utf-8
+# frozen_string_literal: true
 
 require 'spec_helper'
 require 'ice_nine'