diff --git a/Gemfile b/Gemfile
index 0cfa9f88c0..ef1b0f4f77 100644
--- a/Gemfile
+++ b/Gemfile
@@ -11,3 +11,4 @@ gem 'rubocop', '>= 1.31.0'
 gem 'gettext'
 gem 'prism', '>= 0.30.0'
 gem 'webrick'
+gem 'tsort'
diff --git a/test/rdoc/rdoc_generator_darkfish_test.rb b/test/rdoc/rdoc_generator_darkfish_test.rb
index 52ae0601d3..80c2bf0c44 100644
--- a/test/rdoc/rdoc_generator_darkfish_test.rb
+++ b/test/rdoc/rdoc_generator_darkfish_test.rb
@@ -542,7 +542,7 @@ def test_canonical_url_for_index
   def test_canonical_url_for_classes
     top_level = @store.add_file("file.rb")
     top_level.add_class(@klass.class, @klass.name)
-    inner = @klass.add_class(RDoc::NormalClass, "Inner")
+    @klass.add_class(RDoc::NormalClass, "Inner")
 
     @store.options.canonical_root = @options.canonical_root = "https://docs.ruby-lang.org/en/master/"
     @g.generate
@@ -553,7 +553,7 @@ def test_canonical_url_for_classes
   end
 
   def test_canonical_url_for_rdoc_files
-    top_level = @store.add_file("CONTRIBUTING.rdoc", parser: RDoc::Parser::Simple)
+    @store.add_file("CONTRIBUTING.rdoc", parser: RDoc::Parser::Simple)
 
     @store.options.canonical_root = @options.canonical_root = "https://docs.ruby-lang.org/en/master/"
     @g.generate