test: stabilize mailer and signup validation specs

spec/mailers/administrator_notifications/shared/smtp_config_shared.rb

@@ -1,11 +1,9 @@
 # frozen_string_literal: true
 
 RSpec.shared_context 'with smtp config' do
-  before do
-    # We need to use allow_any_instance_of here because smtp_config_set_or_development?
-    # is defined in ApplicationMailer and needs to be stubbed for all mailer instances
-    # rubocop:disable RSpec/AnyInstance
-    allow_any_instance_of(ApplicationMailer).to receive(:smtp_config_set_or_development?).and_return(true)
-    # rubocop:enable RSpec/AnyInstance
+  around do |example|
+    # Set SMTP_ADDRESS so mailers build a Mail::Message in test without touching real SMTP.
+    # Scoped to this shared context to avoid affecting other specs.
+    with_modified_env('SMTP_ADDRESS' => 'smtp.example.com') { example.run }
   end
 end

spec/services/account/sign_up_email_validation_service_spec.rb

@@ -20,7 +20,7 @@ RSpec.describe Account::SignUpEmailValidationService, type: :service do
       it 'raises InvalidEmail with invalid message' do
         allow(ValidEmail2::Address).to receive(:new).with(email).and_return(invalid_email_address)
         expect { service.perform }.to raise_error do |error|
-          expect(error).to be_a(CustomExceptions::Account::InvalidEmail)
+          expect(error.class.name).to eq('CustomExceptions::Account::InvalidEmail')
           expect(error.message).to eq(I18n.t('errors.signup.invalid_email'))
         end
       end
@@ -32,7 +32,7 @@ RSpec.describe Account::SignUpEmailValidationService, type: :service do
       it 'raises InvalidEmail with blocked domain message' do
         allow(ValidEmail2::Address).to receive(:new).with(email).and_return(valid_email_address)
         expect { service.perform }.to raise_error do |error|
-          expect(error).to be_a(CustomExceptions::Account::InvalidEmail)
+          expect(error.class.name).to eq('CustomExceptions::Account::InvalidEmail')
           expect(error.message).to eq(I18n.t('errors.signup.blocked_domain'))
         end
       end
@@ -44,7 +44,7 @@ RSpec.describe Account::SignUpEmailValidationService, type: :service do
       it 'raises InvalidEmail with blocked domain message' do
         allow(ValidEmail2::Address).to receive(:new).with(email).and_return(valid_email_address)
         expect { service.perform }.to raise_error do |error|
-          expect(error).to be_a(CustomExceptions::Account::InvalidEmail)
+          expect(error.class.name).to eq('CustomExceptions::Account::InvalidEmail')
           expect(error.message).to eq(I18n.t('errors.signup.blocked_domain'))
         end
       end
@@ -56,7 +56,7 @@ RSpec.describe Account::SignUpEmailValidationService, type: :service do
       it 'raises InvalidEmail with disposable message' do
         allow(ValidEmail2::Address).to receive(:new).with(email).and_return(disposable_email_address)
         expect { service.perform }.to raise_error do |error|
-          expect(error).to be_a(CustomExceptions::Account::InvalidEmail)
+          expect(error.class.name).to eq('CustomExceptions::Account::InvalidEmail')
           expect(error.message).to eq(I18n.t('errors.signup.disposable_email'))
         end
       end