Add mutation testing with 100% coverage, enforce method coverage

sferik · sferik · commit c7da38c74f5b · 2026-04-02T15:14:46.000-07:00
* Add mutant-minitest and .mutant.yml targeting all HTMLFormatter methods
* Add mutant CI workflow and rake task
* Split tests into test_view_helpers.rb and test_formatter.rb
* Enable method coverage enforcement when Ruby/SimpleCov support it
* Fix warning: suppress method redefinition in test spies
* Fix warning: use @_summary ivar instead of locals for ERB binding
* Remove redundant respond_to? guard for method_coverage?
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
@@ -0,0 +1,16 @@
+name: lint
+
+on: [push, pull_request]
+
+jobs:
+  rubocop:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ruby
+          bundler-cache: true
+
+      - run: bundle exec rubocop
diff --git a/.github/workflows/mutant.yml b/.github/workflows/mutant.yml
@@ -0,0 +1,16 @@
+name: mutant
+
+on: [push, pull_request]
+
+jobs:
+  mutant:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ruby
+          bundler-cache: true
+
+      - run: bundle exec mutant run
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
@@ -34,6 +34,5 @@ jobs:
           bundler-cache: true
         continue-on-error: ${{ (matrix.ruby-version == 'ruby-head') || (matrix.ruby-version == 'jruby-head') || (matrix.ruby-version == 'truffleruby') }}
 
-      - run: |
-          bundle exec rake
+      - run: bundle exec rake test
         continue-on-error: ${{ (matrix.ruby-version == 'ruby-head') || (matrix.ruby-version == 'jruby-head') || (matrix.ruby-version == 'truffleruby') }}
diff --git a/.gitignore b/.gitignore
@@ -28,3 +28,5 @@ coverage
 rdoc
 pkg
 .sass-cache
+/index.html
+/assets/[0-9]*
diff --git a/.mutant.yml b/.mutant.yml
@@ -9,5 +9,4 @@ requires:
   - simplecov-html
 matcher:
   subjects:
-    - SimpleCov::Formatter::HTMLFormatter#coverage_css_class
-    - SimpleCov::Formatter::HTMLFormatter#strength_css_class
+    - SimpleCov::Formatter::HTMLFormatter*
diff --git a/.rubocop.yml b/.rubocop.yml
@@ -62,6 +62,3 @@ Style/TrailingCommaInHashLiteral:
 
 Style/TrailingCommaInArrayLiteral:
   EnforcedStyleForMultiline: "comma"
-
-Gemspec/RequireMFA:
-  Enabled: false
diff --git a/Gemfile b/Gemfile
@@ -16,6 +16,7 @@ end
 
 group :test do
   gem "minitest"
+  gem "mutant-minitest"
 end
 
 group :development do
diff --git a/Gemfile.lock b/Gemfile.lock
@@ -16,8 +16,21 @@ GEM
   remote: https://rubygems.org/
   specs:
     ast (2.4.3)
+    date (3.5.1)
+    date (3.5.1-java)
+    diff-lcs (2.0.0)
     docile (1.4.1)
     drb (2.2.3)
+    erb (6.0.2)
+    erb (6.0.2-java)
+    io-console (0.8.2)
+    io-console (0.8.2-java)
+    irb (1.17.0)
+      pp (>= 0.6.0)
+      prism (>= 1.3.0)
+      rdoc (>= 4.0.0)
+      reline (>= 0.4.2)
+    jar-dependencies (0.5.7)
     json (2.19.3)
     json (2.19.3-java)
     language_server-protocol (3.17.0.5)
@@ -26,6 +39,18 @@ GEM
     minitest (6.0.3)
       drb (~> 2.0)
       prism (~> 1.5)
+    mutant (0.15.1)
+      diff-lcs (>= 1.6, < 3)
+      irb (~> 1.15)
+      parser (~> 3.3.10)
+      regexp_parser (~> 2.10)
+      sorbet-runtime (~> 0.6.0)
+      unparser (~> 0.8.2)
+    mutant-minitest (0.15.1)
+      minitest (>= 5.11, < 7)
+      mutant (= 0.15.1)
+      mutex_m (~> 0.2)
+    mutex_m (0.3.0)
     nokogiri (1.19.2-arm64-darwin)
       racc (~> 1.4)
     nokogiri (1.19.2-java)
@@ -36,12 +61,27 @@ GEM
     parser (3.3.11.1)
       ast (~> 2.4.1)
       racc
+    pp (0.6.3)
+      prettyprint
+    prettyprint (0.2.0)
     prism (1.9.0)
+    psych (5.3.1)
+      date
+      stringio
+    psych (5.3.1-java)
+      date
+      jar-dependencies (>= 0.1.7)
     racc (1.8.1)
     racc (1.8.1-java)
     rainbow (3.1.1)
     rake (13.3.1)
+    rdoc (7.2.0)
+      erb
+      psych (>= 4.0.0)
+      tsort
     regexp_parser (2.11.3)
+    reline (0.6.3)
+      io-console (~> 0.5)
     rubocop (1.86.0)
       json (~> 2.3)
       language_server-protocol (~> 3.17.0.2)
@@ -69,9 +109,16 @@ GEM
       rubocop (>= 1.72.1)
     ruby-progressbar (1.13.0)
     simplecov_json_formatter (0.1.4)
+    sorbet-runtime (0.6.13073)
+    stringio (3.2.0)
+    tsort (0.2.0)
     unicode-display_width (3.2.0)
       unicode-emoji (~> 4.1)
     unicode-emoji (4.2.0)
+    unparser (0.8.2)
+      diff-lcs (>= 1.6, < 3)
+      parser (>= 3.3.0)
+      prism (>= 1.5.1)
 
 PLATFORMS
   arm64-darwin-22
@@ -82,6 +129,7 @@ PLATFORMS
 DEPENDENCIES
   logger
   minitest
+  mutant-minitest
   nokogiri
   rake (>= 11)
   rubocop
diff --git a/Rakefile b/Rakefile
@@ -19,7 +19,12 @@ rescue LoadError
   end
 end
 
-task default: %i[test rubocop]
+desc "Run mutation tests"
+task :mutant do
+  sh "bundle exec mutant run"
+end
+
+task default: %i[test rubocop mutant]
 
 namespace :assets do
   desc "Compiles all assets using esbuild"
diff --git a/lib/simplecov-html.rb b/lib/simplecov-html.rb
@@ -27,7 +27,7 @@ class HTMLFormatter
 
       def initialize(silent: false, inline_assets: false)
         @branch_coverage = SimpleCov.branch_coverage?
-        @method_coverage = SimpleCov.respond_to?(:method_coverage?) && SimpleCov.method_coverage?
+        @method_coverage = SimpleCov.method_coverage?
         @templates = {}
         @inline_assets = inline_assets || ENV.key?("SIMPLECOV_INLINE_ASSETS")
         @public_assets_dir = File.join(File.dirname(__FILE__), "../public/")
@@ -72,21 +72,21 @@ def output_path
       end
 
       def asset_output_path
-        @asset_output_path ||= File.join(output_path, "assets", SimpleCov::Formatter::HTMLFormatter::VERSION).tap do |path|
+        @asset_output_path ||= File.join(output_path, "assets", VERSION).tap do |path|
           FileUtils.mkdir_p(path)
         end
       end
 
       def assets_path(name)
         return asset_inline(name) if @inline_assets
 
-        File.join("./assets", SimpleCov::Formatter::HTMLFormatter::VERSION, name)
+        File.join("./assets", VERSION, name)
       end
 
       def asset_inline(name)
         path = File.join(@public_assets_dir, name)
         base64_content = [File.read(path)].pack("m0")
-        "data:#{CONTENT_TYPES[File.extname(name)]};base64,#{base64_content}"
+        "data:#{CONTENT_TYPES.fetch(File.extname(name))};base64,#{base64_content}"
       end
 
       def formatted_source_file(source_file)
diff --git a/lib/simplecov-html/view_helpers.rb b/lib/simplecov-html/view_helpers.rb
@@ -63,7 +63,7 @@ def timeago(time)
         end
 
         def shortened_filename(source_file)
-          source_file.filename.sub(SimpleCov.root, ".").gsub(%r{^\./}, "")
+          source_file.filename.sub(SimpleCov.root, ".").delete_prefix("./")
         end
 
         def link_to_source_file(source_file)
@@ -76,15 +76,16 @@ def covered_percent(percent)
         end
 
         def to_id(value)
-          value.gsub(/^[^a-zA-Z]+/, "").gsub(/[^a-zA-Z0-9\-_]/, "")
+          value.sub(/\A[^a-zA-Z]+/, "").gsub(/[^a-zA-Z0-9\-_]/, "")
         end
 
         def coverage_summary(stats, show_method_toggle: false)
-          line_stats = build_stats(stats[:covered_lines], stats[:total_lines])
-          branch_stats = build_stats(stats.fetch(:covered_branches, 0), stats.fetch(:total_branches, 0))
-          method_stats = build_stats(stats.fetch(:covered_methods, 0), stats.fetch(:total_methods, 0))
-          # Suppress "assigned but unused variable" warnings — these locals are consumed by the ERB template via binding
-          _ = [line_stats, branch_stats, method_stats, show_method_toggle]
+          @_summary = {
+            line: build_stats(stats.fetch(:covered_lines), stats.fetch(:total_lines)),
+            branch: build_stats(stats.fetch(:covered_branches, 0), stats.fetch(:total_branches, 0)),
+            method: build_stats(stats.fetch(:covered_methods, 0), stats.fetch(:total_methods, 0)),
+            show_method_toggle: show_method_toggle,
+          }
           template("coverage_summary").result(binding)
         end
 
diff --git a/test/coverage_fixtures.rb b/test/coverage_fixtures.rb
@@ -12,7 +12,7 @@ module CoverageFixtures
   }.freeze
 
   SAMPLE_RB = {
-    "lines" => [nil, 1, 1, 1, nil, nil, 1, 0, nil, nil, nil, nil, nil, nil, nil, nil, nil],
+    "lines" => [nil, 1, 1, 1, nil, nil, 1, 0, nil, nil, nil, nil, nil, nil, nil, nil],
   }.freeze
 
   INLINE_RB = {
diff --git a/test/helper.rb b/test/helper.rb
@@ -15,7 +15,12 @@
     minimum_coverage line: 97
   else
     enable_coverage :branch
-    minimum_coverage line: 100, branch: 100
+    minimums = {line: 100, branch: 100}
+    if SimpleCov.respond_to?(:method_coverage_supported?) && SimpleCov.method_coverage_supported?
+      enable_coverage :method
+      minimums[:method] = 100
+    end
+    minimum_coverage minimums
   end
 end
 require "simplecov-html"
diff --git a/test/test_formatter.rb b/test/test_formatter.rb
diff --git a/test/test_mutation.rb b/test/test_mutation.rb
diff --git a/test/test_view_helpers.rb b/test/test_view_helpers.rb
diff --git a/views/coverage_summary.erb b/views/coverage_summary.erb
