Fix `RSpec/SubjectStub` cop (#25550)

Co-authored-by: Claire <claire.github-309c@sitedethib.com>

.rubocop_todo.yml

@@ -409,11 +409,6 @@ RSpec/StubbedMock:
     - 'spec/lib/webfinger_resource_spec.rb'
     - 'spec/services/activitypub/process_collection_service_spec.rb'
 
-RSpec/SubjectStub:
-  Exclude:
-    - 'spec/services/unallow_domain_service_spec.rb'
-    - 'spec/validators/blacklisted_email_validator_spec.rb'
-
 # This cop supports unsafe autocorrection (--autocorrect-all).
 Rails/ApplicationController:
   Exclude:

spec/services/unallow_domain_service_spec.rb

@@ -14,7 +14,7 @@ RSpec.describe UnallowDomainService, type: :service do
 
   context 'with limited federation mode' do
     before do
-      allow(subject).to receive(:whitelist_mode?).and_return(true)
+      allow(Rails.configuration.x).to receive(:whitelist_mode).and_return(true)
     end
 
     describe '#call' do
@@ -40,7 +40,7 @@ RSpec.describe UnallowDomainService, type: :service do
 
   context 'without limited federation mode' do
     before do
-      allow(subject).to receive(:whitelist_mode?).and_return(false)
+      allow(Rails.configuration.x).to receive(:whitelist_mode).and_return(false)
     end
 
     describe '#call' do

spec/validators/blacklisted_email_validator_spec.rb

@@ -11,14 +11,15 @@ RSpec.describe BlacklistedEmailValidator, type: :validator do
 
     before do
       allow(user).to receive(:valid_invitation?).and_return(false)
-      allow_any_instance_of(described_class).to receive(:blocked_email_provider?) { blocked_email }
+      allow(EmailDomainBlock).to receive(:block?) { blocked_email }
     end
 
     context 'when e-mail provider is blocked' do
       let(:blocked_email) { true }
 
       it 'adds error' do
-        expect(subject).to have_received(:add).with(:email, :blocked)
+        described_class.new.validate(user)
+        expect(errors).to have_received(:add).with(:email, :blocked).once
       end
     end
 
@@ -26,7 +27,8 @@ RSpec.describe BlacklistedEmailValidator, type: :validator do
       let(:blocked_email) { false }
 
       it 'does not add errors' do
-        expect(subject).to_not have_received(:add).with(:email, :blocked)
+        described_class.new.validate(user)
+        expect(errors).to_not have_received(:add)
       end
 
       context 'when canonical e-mail is blocked' do
@@ -37,7 +39,8 @@ RSpec.describe BlacklistedEmailValidator, type: :validator do
         end
 
         it 'adds error' do
-          expect(subject).to have_received(:add).with(:email, :taken)
+          described_class.new.validate(user)
+          expect(errors).to have_received(:add).with(:email, :taken).once
         end
       end
     end