Recognize stubbing of described_class in RSpec/SubjectStub

Author: lovro-bikic

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Master (Unreleased)
 
+- Recognize stubbing of `described_class` in `RSpec/SubjectStub`. ([@lovro-bikic])
+
 ## 3.6.0 (2025-04-18)
 
 - Fix false positive in `RSpec/Pending`, where it would mark the default block `it` as an offense. ([@bquorning])

docs/modules/ROOT/pages/cops_rspec.adoc

@@ -6096,6 +6096,16 @@ describe Article do
   end
 end
 
+# bad - described_class stubs are recognized as well
+describe Article do
+  it 'indicates that the author is unknown' do
+    article = double(Article, description: 'by an unknown author')
+    allow(described_class).to receive(:new).and_return(article)
+
+    expect(Article.new.description).to include('by an unknown author')
+  end
+end
+
 # good
 describe Article do
   subject(:article) { Article.new(author: nil) }

lib/rubocop/cop/rspec/subject_stub.rb

@@ -38,6 +38,16 @@ module RSpec
       #     end
       #   end
       #
+      #   # bad - described_class stubs are recognized as well
+      #   describe Article do
+      #     it 'indicates that the author is unknown' do
+      #       article = double(Article, description: 'by an unknown author')
+      #       allow(described_class).to receive(:new).and_return(article)
+      #
+      #       expect(Article.new.description).to include('by an unknown author')
+      #     end
+      #   end
+      #
       #   # good
       #   describe Article do
       #     subject(:article) { Article.new(author: nil) }
@@ -141,7 +151,7 @@ def find_subject_expectations(node, subject_names = [], &block)
           subject_names = [*subject_names, *@explicit_subjects[node]]
           subject_names -= @subject_overrides[node] if @subject_overrides[node]
 
-          names = Set[*subject_names, :subject]
+          names = Set[*subject_names, :subject, :described_class]
           expectation_detected = message_expectation?(node, names)
           return yield(node) if expectation_detected
 

spec/rubocop/cop/rspec/subject_stub_spec.rb

@@ -364,6 +364,17 @@
     RUBY
   end
 
+  it 'flags when described_class is mocked' do
+    expect_offense(<<~RUBY)
+      describe Foo do
+        it 'uses described_class' do
+          expect(described_class).to receive(:bar).and_return(baz)
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Do not stub methods of the object under test.
+        end
+      end
+    RUBY
+  end
+
   it 'flags when there are several top level example groups' do
     expect_offense(<<~RUBY)
       RSpec.describe Foo do